* cleaner/better zlib sources?
@ 2007-03-16 1:04 Linus Torvalds
2007-03-16 1:10 ` Shawn O. Pearce
` (2 more replies)
0 siblings, 3 replies; 79+ messages in thread
From: Linus Torvalds @ 2007-03-16 1:04 UTC (permalink / raw)
To: Git Mailing List
I looked at git profiles yesterday, and some of them are pretty scary. We
spend about 50% of the time under some loads in just zlib uncompression,
and when I actually looked closer at the zlib sources I can kind of
understand why. That thing is horrid.
The sad part is that it looks like it should be quite possible to make
zlib simply just perform better. The profiles seem to say that a lot of
the cost is literally in the "inflate()" state machine code (and by that I
mean *not* the code itself, but literally in the indirect jump generated
by the case-statement).
Now, on any high-performance CPU, doing state-machines by having
for (;;)
switch (data->state) {
...
data->state = NEW_STATE;
continue;
}
(which is what zlib seems to be doing) is just about the worst possible
way to code things.
Now, it's possible that I'm just wrong, but the instruction-level profile
really did pinpoint the "look up state branch pointer and jump to it" as
some of the hottest part of that function. Which is just *evil*. You can
most likely use direct jumps within the loop (zero cost at all on most OoO
CPU's) most of the time, and the entry condition is likely quite
predictable too, so a lot of that overhead seems to be just sad and
unnecessary.
Now, I'm just wondering if anybody knows if there are better zlib
implementations out there? This really looks like it could be a noticeable
performance issue, but I'm lazy and would be much happier to hear that
somebody has already played with optimizing zlib. Especially since I'm not
100% sure it's really going to be noticeable..
Linus
^ permalink raw reply [flat|nested] 79+ messages in thread
* Re: cleaner/better zlib sources?
2007-03-16 1:04 cleaner/better zlib sources? Linus Torvalds
@ 2007-03-16 1:10 ` Shawn O. Pearce
2007-03-16 1:11 ` Jeff Garzik
2007-03-16 1:33 ` Davide Libenzi
2 siblings, 0 replies; 79+ messages in thread
From: Shawn O. Pearce @ 2007-03-16 1:10 UTC (permalink / raw)
To: Linus Torvalds; +Cc: Git Mailing List
Linus Torvalds <torvalds@linux-foundation.org> wrote:
> I looked at git profiles yesterday, and some of them are pretty scary. We
> spend about 50% of the time under some loads in just zlib uncompression,
> and when I actually looked closer at the zlib sources I can kind of
> understand why. That thing is horrid.
Yes. This is actually one of the motivations behind pack v4.
We don't store the "important bits" of commits and trees in zlib
compressed format at all; allowing us to completely bypass the
inflate() penalty you describe.
We're already much faster on the linux-2.6 kernel tree, and that's
*with* converting the pack raw data into text, then reparsing
that text into a struct commit* or a struct name_entry using the
current code. We're also planning on reworking those parsers to
parse the raw pack data, allowing us to save some very unnecessary
raw->string->raw conversion time.
But Nico and I still looking to use zlib for commit messages and
blob content, so any improvements to inflate (or its replacement)
would still be most helpful.
--
Shawn.
^ permalink raw reply [flat|nested] 79+ messages in thread
* Re: cleaner/better zlib sources?
2007-03-16 1:04 cleaner/better zlib sources? Linus Torvalds
2007-03-16 1:10 ` Shawn O. Pearce
@ 2007-03-16 1:11 ` Jeff Garzik
2007-03-16 1:14 ` Matt Mackall
2007-03-16 1:46 ` Linus Torvalds
2007-03-16 1:33 ` Davide Libenzi
2 siblings, 2 replies; 79+ messages in thread
From: Jeff Garzik @ 2007-03-16 1:11 UTC (permalink / raw)
To: Linus Torvalds; +Cc: Git Mailing List, mpm, bcrl
Linus Torvalds wrote:
> Now, it's possible that I'm just wrong, but the instruction-level profile
> really did pinpoint the "look up state branch pointer and jump to it" as
> some of the hottest part of that function. Which is just *evil*. You can
ISTR there are a bunch of state transitions per byte, which would make
sense that it shows up on profiles.
> Now, I'm just wondering if anybody knows if there are better zlib
> implementations out there? This really looks like it could be a noticeable
> performance issue, but I'm lazy and would be much happier to hear that
> somebody has already played with optimizing zlib. Especially since I'm not
> 100% sure it's really going to be noticeable..
I could have sworn that either Matt Mackall or Ben LaHaise had cleaned
up the existing zlib so much that it was practically a new
implementation. I'm not aware of any open source implementations
independent of zlib (except maybe that C++ behemoth, 7zip).
Jeff
^ permalink raw reply [flat|nested] 79+ messages in thread
* Re: cleaner/better zlib sources?
2007-03-16 1:11 ` Jeff Garzik
@ 2007-03-16 1:14 ` Matt Mackall
2007-03-16 1:46 ` Linus Torvalds
1 sibling, 0 replies; 79+ messages in thread
From: Matt Mackall @ 2007-03-16 1:14 UTC (permalink / raw)
To: Jeff Garzik; +Cc: Linus Torvalds, Git Mailing List, bcrl
On Thu, Mar 15, 2007 at 09:11:49PM -0400, Jeff Garzik wrote:
> Linus Torvalds wrote:
> >Now, it's possible that I'm just wrong, but the instruction-level profile
> >really did pinpoint the "look up state branch pointer and jump to it" as
> >some of the hottest part of that function. Which is just *evil*. You can
>
> ISTR there are a bunch of state transitions per byte, which would make
> sense that it shows up on profiles.
Yep, not surprising.
> >Now, I'm just wondering if anybody knows if there are better zlib
> >implementations out there? This really looks like it could be a noticeable
> >performance issue, but I'm lazy and would be much happier to hear that
> >somebody has already played with optimizing zlib. Especially since I'm not
> >100% sure it's really going to be noticeable..
>
> I could have sworn that either Matt Mackall or Ben LaHaise had cleaned
> up the existing zlib so much that it was practically a new
> implementation. I'm not aware of any open source implementations
> independent of zlib (except maybe that C++ behemoth, 7zip).
I cleaned up the version in lib/ that's used for boot on most systems.
It's quite a bit simpler and cleaner than the code lib/zlib (and
elsewhere!). But making it faster is another matter entirely - I don't
know off-hand how the two compare.
--
Mathematics is the supreme nostalgia of our time.
^ permalink raw reply [flat|nested] 79+ messages in thread
* Re: cleaner/better zlib sources?
2007-03-16 1:04 cleaner/better zlib sources? Linus Torvalds
2007-03-16 1:10 ` Shawn O. Pearce
2007-03-16 1:11 ` Jeff Garzik
@ 2007-03-16 1:33 ` Davide Libenzi
2007-03-16 2:06 ` Davide Libenzi
2 siblings, 1 reply; 79+ messages in thread
From: Davide Libenzi @ 2007-03-16 1:33 UTC (permalink / raw)
To: Linus Torvalds; +Cc: Git Mailing List
On Thu, 15 Mar 2007, Linus Torvalds wrote:
>
> I looked at git profiles yesterday, and some of them are pretty scary. We
> spend about 50% of the time under some loads in just zlib uncompression,
> and when I actually looked closer at the zlib sources I can kind of
> understand why. That thing is horrid.
>
> The sad part is that it looks like it should be quite possible to make
> zlib simply just perform better. The profiles seem to say that a lot of
> the cost is literally in the "inflate()" state machine code (and by that I
> mean *not* the code itself, but literally in the indirect jump generated
> by the case-statement).
>
> Now, on any high-performance CPU, doing state-machines by having
>
> for (;;)
> switch (data->state) {
> ...
> data->state = NEW_STATE;
> continue;
> }
>
> (which is what zlib seems to be doing) is just about the worst possible
> way to code things.
A quick hack would be to just define:
#define SWITCH_LBL(n) \
case n: \
lbl_##n:
#define STATE_CHANGE(s) \
state->mode = s; \
goto lbl_##s;
Then replace all the "state->mode = STATE; break;" into STATE_CHANGE(STATE);
I'm giving it a try as we speak ...
- Davide
^ permalink raw reply [flat|nested] 79+ messages in thread
* Re: cleaner/better zlib sources?
2007-03-16 1:11 ` Jeff Garzik
2007-03-16 1:14 ` Matt Mackall
@ 2007-03-16 1:46 ` Linus Torvalds
2007-03-16 1:54 ` Linus Torvalds
1 sibling, 1 reply; 79+ messages in thread
From: Linus Torvalds @ 2007-03-16 1:46 UTC (permalink / raw)
To: Jeff Garzik; +Cc: Git Mailing List, mpm, bcrl
On Thu, 15 Mar 2007, Jeff Garzik wrote:
>
> ISTR there are a bunch of state transitions per byte, which would make sense
> that it shows up on profiles.
Yeah. I only looked at the kernel sources (which include a cleaned-up
older version of zlib), but they seemed to match the disassembly that I
saw when doing the instruction-level profiling.
The code *sometimes* falls through from one state to another, ie there's a
case where zlib does:
...
case DICTID:
NEEDBITS(32);
strm->adler = state->check = REVERSE(hold);
INITBITS();
state->mode = DICT;
case DICT:
...
which will obviously generate fine code. There's a few other examples of
that, *BUT* most of the stuff is just horrid, like
case HEAD:
if (state->wrap == 0) {
state->mode = TYPEDO;
break;
}
where the "break" (which simply breaks out of the case-statement, and thus
just loops back to it:
for (;;)
switch (state->mode) {
thing is nasty nasty nasty).
A trivial thing to do is to just replace such
state->mode = xxx;
break;
with
state->mode = xxx;
goto xxx_mode;
and all of that complicated run-time code *just*goes*away* and is replaced
by a relative no-op (ie an unconditional direct jump).
Some of them are slightly more complex, like
state->mode = hold & 0x200 ? DICTID : TYPE;
INITBITS();
break;
which would need to be rewritten as
old_hold = hold;
INITBITS();
if (old_hold & 0x200) {
state->mode = DICTID;
goto dictid_mode;
}
state->mode = TYPE;
goto dictid_mode;
but while that looks more complicated on a source code level it's a *lot*
easier for a CPU to actually execute.
Same obvious performance problems go for
case STORED:
...
case COPY:
copy = state->length;
if (copy) {
...
state->length -= copy;
break;
}
Tracev((stderr, "inflate: stored end\n"));
state->mode = TYPE;
break;
notice how when you get to the COPY state it will actually have nicely
fallen through from STORED (one of the places where it does that), but
then it will go through the expensive indirect jump not just once, but at
least *TWICE* just to get to the TYPE thing, because you'll first have to
re-enter COPY with a count of zero to get to the place where it sets TYPE,
and then does the indirect jump immediately again!
In other words, the code is *incredibly* badly written from a performance
angle.
Yeah, a perfect compiler could do this all for us even with unchanged zlib
source code, but (a) gcc isn't perfect and (b) I don't really think
anything else is either, although if things like this happen as part of
gzip in SpecInt, I wouldn't be surprised by compilers doing things like
this just to look good ;)
Especially with something like git, where we know that most of the time we
have the full input buffer (so inflate() generally won't be called in the
"middle" of a inflate event), we probably have a very well-defined start
state too, so we'd actually predict perfectlyon the *first* indirect jump
if we just never did any more of them.
> I could have sworn that either Matt Mackall or Ben LaHaise had cleaned up the
> existing zlib so much that it was practically a new implementation. I'm not
> aware of any open source implementations independent of zlib (except maybe
> that C++ behemoth, 7zip).
I looked at the latest release (1.2.3), so either Matt/Ben hasn't been
merged, or this wasn't part of the thing they looked at.
Linus
^ permalink raw reply [flat|nested] 79+ messages in thread
* Re: cleaner/better zlib sources?
2007-03-16 1:46 ` Linus Torvalds
@ 2007-03-16 1:54 ` Linus Torvalds
2007-03-16 2:43 ` Davide Libenzi
0 siblings, 1 reply; 79+ messages in thread
From: Linus Torvalds @ 2007-03-16 1:54 UTC (permalink / raw)
To: Jeff Garzik; +Cc: Git Mailing List, mpm, bcrl, Davide Libenzi
On Thu, 15 Mar 2007, Linus Torvalds wrote:
>
> Same obvious performance problems go for
>
> case COPY:
As an example, I *think* this patch to zlib-1.2.3 not only generates
better code, but is (a) shorter and (b) more logical anyway.
Together with Davide's suggestion on using C macro expansion to make most
of the mode switches simple branches, it might get rid of most of the
indirect branches (to get rid of them all, you'd have to also find the
places where we *don't* set a new state, because it stays the same like
this one, and the ones where we have conditionals on what the mode is
going to be..
Of course, the zlib sources are pretty horrid for other reasons (K&R
source code meant to be compiled on 16-bit architectures too). But that's
a separate issue, and at least shouldn't affect the resulting code
quality..
Linus
---
inflate.c | 3 +--
1 files changed, 1 insertions(+), 2 deletions(-)
diff --git a/inflate.c b/inflate.c
index 792fdee..fb26f39 100644
--- a/inflate.c
+++ b/inflate.c
@@ -819,7 +819,7 @@ int flush;
state->mode = COPY;
case COPY:
copy = state->length;
- if (copy) {
+ while (copy) {
if (copy > have) copy = have;
if (copy > left) copy = left;
if (copy == 0) goto inf_leave;
@@ -829,7 +829,6 @@ int flush;
left -= copy;
put += copy;
state->length -= copy;
- break;
}
Tracev((stderr, "inflate: stored end\n"));
state->mode = TYPE;
^ permalink raw reply related [flat|nested] 79+ messages in thread
* Re: cleaner/better zlib sources?
2007-03-16 1:33 ` Davide Libenzi
@ 2007-03-16 2:06 ` Davide Libenzi
0 siblings, 0 replies; 79+ messages in thread
From: Davide Libenzi @ 2007-03-16 2:06 UTC (permalink / raw)
To: Linus Torvalds; +Cc: Git Mailing List
On Thu, 15 Mar 2007, Davide Libenzi wrote:
> On Thu, 15 Mar 2007, Linus Torvalds wrote:
>
> >
> > I looked at git profiles yesterday, and some of them are pretty scary. We
> > spend about 50% of the time under some loads in just zlib uncompression,
> > and when I actually looked closer at the zlib sources I can kind of
> > understand why. That thing is horrid.
> >
> > The sad part is that it looks like it should be quite possible to make
> > zlib simply just perform better. The profiles seem to say that a lot of
> > the cost is literally in the "inflate()" state machine code (and by that I
> > mean *not* the code itself, but literally in the indirect jump generated
> > by the case-statement).
> >
> > Now, on any high-performance CPU, doing state-machines by having
> >
> > for (;;)
> > switch (data->state) {
> > ...
> > data->state = NEW_STATE;
> > continue;
> > }
> >
> > (which is what zlib seems to be doing) is just about the worst possible
> > way to code things.
>
> A quick hack would be to just define:
>
> #define SWITCH_LBL(n) \
> case n: \
> lbl_##n:
>
> #define STATE_CHANGE(s) \
> state->mode = s; \
> goto lbl_##s;
>
> Then replace all the "state->mode = STATE; break;" into STATE_CHANGE(STATE);
> I'm giving it a try as we speak ...
I get about 5-6% boost with it AFAICS ...
- Davide
^ permalink raw reply [flat|nested] 79+ messages in thread
* Re: cleaner/better zlib sources?
2007-03-16 1:54 ` Linus Torvalds
@ 2007-03-16 2:43 ` Davide Libenzi
2007-03-16 2:56 ` Linus Torvalds
0 siblings, 1 reply; 79+ messages in thread
From: Davide Libenzi @ 2007-03-16 2:43 UTC (permalink / raw)
To: Linus Torvalds; +Cc: Jeff Garzik, Git Mailing List, mpm, bcrl
On Thu, 15 Mar 2007, Linus Torvalds wrote:
>
>
> On Thu, 15 Mar 2007, Linus Torvalds wrote:
> >
> > Same obvious performance problems go for
> >
> > case COPY:
>
> As an example, I *think* this patch to zlib-1.2.3 not only generates
> better code, but is (a) shorter and (b) more logical anyway.
>
> Together with Davide's suggestion on using C macro expansion to make most
> of the mode switches simple branches, it might get rid of most of the
> indirect branches (to get rid of them all, you'd have to also find the
> places where we *don't* set a new state, because it stays the same like
> this one, and the ones where we have conditionals on what the mode is
> going to be..
That's the diff against 1.2.3, but it does not seem to make an substantial
difference in my Opteron ...
- Davide
Index: zlib-1.2.3.quilt/inflate.c
===================================================================
--- zlib-1.2.3.quilt.orig/inflate.c 2007-03-15 18:17:19.000000000 -0700
+++ zlib-1.2.3.quilt/inflate.c 2007-03-15 18:31:14.000000000 -0700
@@ -551,6 +551,15 @@
will return Z_BUF_ERROR if it has not reached the end of the stream.
*/
+#define CASE_DECL(n) \
+ case n: \
+ lbl_##n:
+
+#define STATE_CHANGE(s) do { \
+ state->mode = s; \
+ goto lbl_##s; \
+} while (0)
+
int ZEXPORT inflate(strm, flush)
z_streamp strm;
int flush;
@@ -586,10 +595,9 @@
ret = Z_OK;
for (;;)
switch (state->mode) {
- case HEAD:
+ CASE_DECL(HEAD)
if (state->wrap == 0) {
- state->mode = TYPEDO;
- break;
+ STATE_CHANGE(TYPEDO);
}
NEEDBITS(16);
#ifdef GUNZIP
@@ -597,8 +605,7 @@
state->check = crc32(0L, Z_NULL, 0);
CRC2(state->check, hold);
INITBITS();
- state->mode = FLAGS;
- break;
+ STATE_CHANGE(FLAGS);
}
state->flags = 0; /* expect zlib header */
if (state->head != Z_NULL)
@@ -609,20 +616,17 @@
#endif
((BITS(8) << 8) + (hold >> 8)) % 31) {
strm->msg = (char *)"incorrect header check";
- state->mode = BAD;
- break;
+ STATE_CHANGE(BAD);
}
if (BITS(4) != Z_DEFLATED) {
strm->msg = (char *)"unknown compression method";
- state->mode = BAD;
- break;
+ STATE_CHANGE(BAD);
}
DROPBITS(4);
len = BITS(4) + 8;
if (len > state->wbits) {
strm->msg = (char *)"invalid window size";
- state->mode = BAD;
- break;
+ STATE_CHANGE(BAD);
}
state->dmax = 1U << len;
Tracev((stderr, "inflate: zlib header ok\n"));
@@ -631,32 +635,30 @@
INITBITS();
break;
#ifdef GUNZIP
- case FLAGS:
+ CASE_DECL(FLAGS)
NEEDBITS(16);
state->flags = (int)(hold);
if ((state->flags & 0xff) != Z_DEFLATED) {
strm->msg = (char *)"unknown compression method";
- state->mode = BAD;
- break;
+ STATE_CHANGE(BAD);
}
if (state->flags & 0xe000) {
strm->msg = (char *)"unknown header flags set";
- state->mode = BAD;
- break;
+ STATE_CHANGE(BAD);
}
if (state->head != Z_NULL)
state->head->text = (int)((hold >> 8) & 1);
if (state->flags & 0x0200) CRC2(state->check, hold);
INITBITS();
state->mode = TIME;
- case TIME:
+ CASE_DECL(TIME)
NEEDBITS(32);
if (state->head != Z_NULL)
state->head->time = hold;
if (state->flags & 0x0200) CRC4(state->check, hold);
INITBITS();
state->mode = OS;
- case OS:
+ CASE_DECL(OS)
NEEDBITS(16);
if (state->head != Z_NULL) {
state->head->xflags = (int)(hold & 0xff);
@@ -665,7 +667,7 @@
if (state->flags & 0x0200) CRC2(state->check, hold);
INITBITS();
state->mode = EXLEN;
- case EXLEN:
+ CASE_DECL(EXLEN)
if (state->flags & 0x0400) {
NEEDBITS(16);
state->length = (unsigned)(hold);
@@ -677,7 +679,7 @@
else if (state->head != Z_NULL)
state->head->extra = Z_NULL;
state->mode = EXTRA;
- case EXTRA:
+ CASE_DECL(EXTRA)
if (state->flags & 0x0400) {
copy = state->length;
if (copy > have) copy = have;
@@ -699,7 +701,7 @@
}
state->length = 0;
state->mode = NAME;
- case NAME:
+ CASE_DECL(NAME)
if (state->flags & 0x0800) {
if (have == 0) goto inf_leave;
copy = 0;
@@ -720,7 +722,7 @@
state->head->name = Z_NULL;
state->length = 0;
state->mode = COMMENT;
- case COMMENT:
+ CASE_DECL(COMMENT)
if (state->flags & 0x1000) {
if (have == 0) goto inf_leave;
copy = 0;
@@ -740,13 +742,12 @@
else if (state->head != Z_NULL)
state->head->comment = Z_NULL;
state->mode = HCRC;
- case HCRC:
+ CASE_DECL(HCRC)
if (state->flags & 0x0200) {
NEEDBITS(16);
if (hold != (state->check & 0xffff)) {
strm->msg = (char *)"header crc mismatch";
- state->mode = BAD;
- break;
+ STATE_CHANGE(BAD);
}
INITBITS();
}
@@ -755,28 +756,26 @@
state->head->done = 1;
}
strm->adler = state->check = crc32(0L, Z_NULL, 0);
- state->mode = TYPE;
- break;
+ STATE_CHANGE(TYPE);
#endif
- case DICTID:
+ CASE_DECL(DICTID)
NEEDBITS(32);
strm->adler = state->check = REVERSE(hold);
INITBITS();
state->mode = DICT;
- case DICT:
+ CASE_DECL(DICT)
if (state->havedict == 0) {
RESTORE();
return Z_NEED_DICT;
}
strm->adler = state->check = adler32(0L, Z_NULL, 0);
state->mode = TYPE;
- case TYPE:
+ CASE_DECL(TYPE)
if (flush == Z_BLOCK) goto inf_leave;
- case TYPEDO:
+ CASE_DECL(TYPEDO)
if (state->last) {
BYTEBITS();
- state->mode = CHECK;
- break;
+ STATE_CHANGE(CHECK);
}
NEEDBITS(3);
state->last = BITS(1);
@@ -785,39 +784,38 @@
case 0: /* stored block */
Tracev((stderr, "inflate: stored block%s\n",
state->last ? " (last)" : ""));
- state->mode = STORED;
- break;
+ DROPBITS(2);
+ STATE_CHANGE(STORED);
case 1: /* fixed block */
fixedtables(state);
Tracev((stderr, "inflate: fixed codes block%s\n",
state->last ? " (last)" : ""));
- state->mode = LEN; /* decode codes */
- break;
+ DROPBITS(2);
+ STATE_CHANGE(LEN);
case 2: /* dynamic block */
Tracev((stderr, "inflate: dynamic codes block%s\n",
state->last ? " (last)" : ""));
- state->mode = TABLE;
- break;
+ DROPBITS(2);
+ STATE_CHANGE(TABLE);
case 3:
+ DROPBITS(2);
strm->msg = (char *)"invalid block type";
- state->mode = BAD;
+ STATE_CHANGE(BAD);
}
- DROPBITS(2);
break;
- case STORED:
+ CASE_DECL(STORED)
BYTEBITS(); /* go to byte boundary */
NEEDBITS(32);
if ((hold & 0xffff) != ((hold >> 16) ^ 0xffff)) {
strm->msg = (char *)"invalid stored block lengths";
- state->mode = BAD;
- break;
+ STATE_CHANGE(BAD);
}
state->length = (unsigned)hold & 0xffff;
Tracev((stderr, "inflate: stored length %u\n",
state->length));
INITBITS();
state->mode = COPY;
- case COPY:
+ CASE_DECL(COPY)
copy = state->length;
if (copy) {
if (copy > have) copy = have;
@@ -832,9 +830,8 @@
break;
}
Tracev((stderr, "inflate: stored end\n"));
- state->mode = TYPE;
- break;
- case TABLE:
+ STATE_CHANGE(TYPE);
+ CASE_DECL(TABLE)
NEEDBITS(14);
state->nlen = BITS(5) + 257;
DROPBITS(5);
@@ -845,14 +842,13 @@
#ifndef PKZIP_BUG_WORKAROUND
if (state->nlen > 286 || state->ndist > 30) {
strm->msg = (char *)"too many length or distance symbols";
- state->mode = BAD;
- break;
+ STATE_CHANGE(BAD);
}
#endif
Tracev((stderr, "inflate: table sizes ok\n"));
state->have = 0;
state->mode = LENLENS;
- case LENLENS:
+ CASE_DECL(LENLENS)
while (state->have < state->ncode) {
NEEDBITS(3);
state->lens[order[state->have++]] = (unsigned short)BITS(3);
@@ -867,13 +863,12 @@
&(state->lenbits), state->work);
if (ret) {
strm->msg = (char *)"invalid code lengths set";
- state->mode = BAD;
- break;
+ STATE_CHANGE(BAD);
}
Tracev((stderr, "inflate: code lengths ok\n"));
state->have = 0;
state->mode = CODELENS;
- case CODELENS:
+ CASE_DECL(CODELENS)
while (state->have < state->nlen + state->ndist) {
for (;;) {
this = state->lencode[BITS(state->lenbits)];
@@ -891,8 +886,7 @@
DROPBITS(this.bits);
if (state->have == 0) {
strm->msg = (char *)"invalid bit length repeat";
- state->mode = BAD;
- break;
+ STATE_CHANGE(BAD);
}
len = state->lens[state->have - 1];
copy = 3 + BITS(2);
@@ -914,17 +908,13 @@
}
if (state->have + copy > state->nlen + state->ndist) {
strm->msg = (char *)"invalid bit length repeat";
- state->mode = BAD;
- break;
+ STATE_CHANGE(BAD);
}
while (copy--)
state->lens[state->have++] = (unsigned short)len;
}
}
- /* handle error breaks in while */
- if (state->mode == BAD) break;
-
/* build code tables */
state->next = state->codes;
state->lencode = (code const FAR *)(state->next);
@@ -933,8 +923,7 @@
&(state->lenbits), state->work);
if (ret) {
strm->msg = (char *)"invalid literal/lengths set";
- state->mode = BAD;
- break;
+ STATE_CHANGE(BAD);
}
state->distcode = (code const FAR *)(state->next);
state->distbits = 6;
@@ -942,12 +931,11 @@
&(state->next), &(state->distbits), state->work);
if (ret) {
strm->msg = (char *)"invalid distances set";
- state->mode = BAD;
- break;
+ STATE_CHANGE(BAD);
}
Tracev((stderr, "inflate: codes ok\n"));
state->mode = LEN;
- case LEN:
+ CASE_DECL(LEN)
if (have >= 6 && left >= 258) {
RESTORE();
inflate_fast(strm, out);
@@ -975,22 +963,19 @@
Tracevv((stderr, this.val >= 0x20 && this.val < 0x7f ?
"inflate: literal '%c'\n" :
"inflate: literal 0x%02x\n", this.val));
- state->mode = LIT;
- break;
+ STATE_CHANGE(LIT);
}
if (this.op & 32) {
Tracevv((stderr, "inflate: end of block\n"));
- state->mode = TYPE;
- break;
+ STATE_CHANGE(TYPE);
}
if (this.op & 64) {
strm->msg = (char *)"invalid literal/length code";
- state->mode = BAD;
- break;
+ STATE_CHANGE(BAD);
}
state->extra = (unsigned)(this.op) & 15;
state->mode = LENEXT;
- case LENEXT:
+ CASE_DECL(LENEXT)
if (state->extra) {
NEEDBITS(state->extra);
state->length += BITS(state->extra);
@@ -998,7 +983,7 @@
}
Tracevv((stderr, "inflate: length %u\n", state->length));
state->mode = DIST;
- case DIST:
+ CASE_DECL(DIST)
for (;;) {
this = state->distcode[BITS(state->distbits)];
if ((unsigned)(this.bits) <= bits) break;
@@ -1017,13 +1002,12 @@
DROPBITS(this.bits);
if (this.op & 64) {
strm->msg = (char *)"invalid distance code";
- state->mode = BAD;
- break;
+ STATE_CHANGE(BAD);
}
state->offset = (unsigned)this.val;
state->extra = (unsigned)(this.op) & 15;
state->mode = DISTEXT;
- case DISTEXT:
+ CASE_DECL(DISTEXT)
if (state->extra) {
NEEDBITS(state->extra);
state->offset += BITS(state->extra);
@@ -1032,18 +1016,16 @@
#ifdef INFLATE_STRICT
if (state->offset > state->dmax) {
strm->msg = (char *)"invalid distance too far back";
- state->mode = BAD;
- break;
+ STATE_CHANGE(BAD);
}
#endif
if (state->offset > state->whave + out - left) {
strm->msg = (char *)"invalid distance too far back";
- state->mode = BAD;
- break;
+ STATE_CHANGE(BAD);
}
Tracevv((stderr, "inflate: distance %u\n", state->offset));
state->mode = MATCH;
- case MATCH:
+ CASE_DECL(MATCH)
if (left == 0) goto inf_leave;
copy = out - left;
if (state->offset > copy) { /* copy from window */
@@ -1066,15 +1048,15 @@
do {
*put++ = *from++;
} while (--copy);
- if (state->length == 0) state->mode = LEN;
+ if (state->length == 0)
+ STATE_CHANGE(LEN);
break;
- case LIT:
+ CASE_DECL(LIT)
if (left == 0) goto inf_leave;
*put++ = (unsigned char)(state->length);
left--;
- state->mode = LEN;
- break;
- case CHECK:
+ STATE_CHANGE(LEN);
+ CASE_DECL(CHECK)
if (state->wrap) {
NEEDBITS(32);
out -= left;
@@ -1090,36 +1072,34 @@
#endif
REVERSE(hold)) != state->check) {
strm->msg = (char *)"incorrect data check";
- state->mode = BAD;
- break;
+ STATE_CHANGE(BAD);
}
INITBITS();
Tracev((stderr, "inflate: check matches trailer\n"));
}
#ifdef GUNZIP
state->mode = LENGTH;
- case LENGTH:
+ CASE_DECL(LENGTH)
if (state->wrap && state->flags) {
NEEDBITS(32);
if (hold != (state->total & 0xffffffffUL)) {
strm->msg = (char *)"incorrect length check";
- state->mode = BAD;
- break;
+ STATE_CHANGE(BAD);
}
INITBITS();
Tracev((stderr, "inflate: length matches trailer\n"));
}
#endif
state->mode = DONE;
- case DONE:
+ CASE_DECL(DONE)
ret = Z_STREAM_END;
goto inf_leave;
- case BAD:
+ CASE_DECL(BAD)
ret = Z_DATA_ERROR;
goto inf_leave;
- case MEM:
+ CASE_DECL(MEM)
return Z_MEM_ERROR;
- case SYNC:
+ CASE_DECL(SYNC)
default:
return Z_STREAM_ERROR;
}
^ permalink raw reply [flat|nested] 79+ messages in thread
* Re: cleaner/better zlib sources?
2007-03-16 2:43 ` Davide Libenzi
@ 2007-03-16 2:56 ` Linus Torvalds
2007-03-16 3:16 ` Davide Libenzi
0 siblings, 1 reply; 79+ messages in thread
From: Linus Torvalds @ 2007-03-16 2:56 UTC (permalink / raw)
To: Davide Libenzi; +Cc: Jeff Garzik, Git Mailing List, mpm, bcrl
On Thu, 15 Mar 2007, Davide Libenzi wrote:
>
> That's the diff against 1.2.3, but it does not seem to make an substantial
> difference in my Opteron ...
But the "goto" stuff you did is 5-6%?
Is that 5-6% of total git costs, or just of inflate() itself?
Linus
^ permalink raw reply [flat|nested] 79+ messages in thread
* Re: cleaner/better zlib sources?
2007-03-16 2:56 ` Linus Torvalds
@ 2007-03-16 3:16 ` Davide Libenzi
2007-03-16 16:21 ` Linus Torvalds
0 siblings, 1 reply; 79+ messages in thread
From: Davide Libenzi @ 2007-03-16 3:16 UTC (permalink / raw)
To: Linus Torvalds; +Cc: Jeff Garzik, Git Mailing List, mpm, bcrl
On Thu, 15 Mar 2007, Linus Torvalds wrote:
>
>
> On Thu, 15 Mar 2007, Davide Libenzi wrote:
> >
> > That's the diff against 1.2.3, but it does not seem to make an substantial
> > difference in my Opteron ...
>
> But the "goto" stuff you did is 5-6%?
>
> Is that 5-6% of total git costs, or just of inflate() itself?
Didn't do proper cache warmup and test time was fairly short. Now I'm not
able to notice substantial differences.
Hacked up test case below ...
- Davide
/* example.c -- usage example of the zlib compression library
* Copyright (C) 1995-2004 Jean-loup Gailly.
* For conditions of distribution and use, see copyright notice in zlib.h
*/
/* @(#) $Id$ */
#include <sys/time.h>
#include <stdio.h>
#include <string.h>
#include <stdlib.h>
#include <time.h>
#include "zlib.h"
#define CHECK_ERR(err, msg) do { \
if (err != Z_OK) { \
fprintf(stderr, "%s error: %d\n", msg, err); \
exit(1); \
} \
} while (0)
unsigned long long getustime(void) {
struct timeval tm;
gettimeofday(&tm, NULL);
return tm.tv_sec * 1000000ULL + tm.tv_usec;
}
/* ===========================================================================
* Test deflate() with large buffers and dynamic change of compression level
*/
void do_defl(Byte *compr, uLong *comprLen,
Byte *uncompr, uLong uncomprLen) {
z_stream c_stream; /* compression stream */
int err;
c_stream.zalloc = (alloc_func)0;
c_stream.zfree = (free_func)0;
c_stream.opaque = (voidpf)0;
err = deflateInit(&c_stream, Z_BEST_SPEED);
CHECK_ERR(err, "deflateInit");
c_stream.next_out = compr;
c_stream.avail_out = (uInt) *comprLen;
/* At this point, uncompr is still mostly zeroes, so it should compress
* very well:
*/
c_stream.next_in = uncompr;
c_stream.avail_in = (uInt) uncomprLen;
err = deflate(&c_stream, Z_FINISH);
if (err != Z_STREAM_END) {
fprintf(stderr, "whoops, got %d instead of Z_STREAM_END\n", err);
exit(1);
}
err = deflateEnd(&c_stream);
CHECK_ERR(err, "deflateEnd");
*comprLen = c_stream.next_out - compr;
}
/* ===========================================================================
* Test inflate() with large buffers
*/
void do_infl(Byte *compr, uLong comprLen,
Byte *uncompr, uLong *uncomprLen) {
int err;
z_stream d_stream; /* decompression stream */
d_stream.zalloc = (alloc_func)0;
d_stream.zfree = (free_func)0;
d_stream.opaque = (voidpf)0;
d_stream.next_in = compr;
d_stream.avail_in = (uInt)comprLen;
err = inflateInit(&d_stream);
CHECK_ERR(err, "inflateInit");
d_stream.next_out = uncompr; /* discard the output */
d_stream.avail_out = (uInt) *uncomprLen;
err = inflate(&d_stream, Z_FULL_FLUSH);
if (err != Z_STREAM_END) {
fprintf(stderr, "deflate should report Z_STREAM_END\n");
exit(1);
}
err = inflateEnd(&d_stream);
CHECK_ERR(err, "inflateEnd");
*uncomprLen = d_stream.next_out - uncompr;
}
int main(int ac, char **av) {
uLong i, n, clen, ulen, size = 8 * 1024 * 1024, range = 256;
Byte *ubuf, *cbuf, *tbuf;
unsigned long long ts, te;
srand(1);
ulen = size;
clen = 2 * ulen;
ubuf = malloc(ulen);
tbuf = malloc(ulen);
cbuf = malloc(clen);
for (i = 0; i < ulen; i++)
ubuf[i] = (Byte) (rand() % range);
/* Warming up ... */
do_defl(cbuf, &clen, ubuf, ulen);
do_infl(cbuf, clen, tbuf, &ulen);
if (ulen != size) {
fprintf(stderr, "size mismatch %lu instead of %lu\n",
(unsigned long) ulen, (unsigned long) size);
return 1;
}
if (memcmp(tbuf, ubuf, size)) {
fprintf(stderr, "whoops! we did not get back the same data\n");
return 2;
}
/* Test ... */
ts = getustime();
n = 0;
do {
for (i = 0; i < 16; i++) {
ulen = size;
do_infl(cbuf, clen, ubuf, &ulen);
}
n += i;
te = getustime();
} while (te - ts < 2 * 1000000);
fprintf(stdout, "us time / cycle = %llu\n", (te - ts) / n);
return 0;
}
^ permalink raw reply [flat|nested] 79+ messages in thread
* Re: cleaner/better zlib sources?
2007-03-16 3:16 ` Davide Libenzi
@ 2007-03-16 16:21 ` Linus Torvalds
2007-03-16 16:24 ` Davide Libenzi
` (2 more replies)
0 siblings, 3 replies; 79+ messages in thread
From: Linus Torvalds @ 2007-03-16 16:21 UTC (permalink / raw)
To: Davide Libenzi; +Cc: Jeff Garzik, Git Mailing List, mpm, bcrl
On Thu, 15 Mar 2007, Davide Libenzi wrote:
>
> Hacked up test case below ...
This one seems to do benchmarking with 8MB buffers if I read it right
(didn't try).
The normal size for the performance-critical git objects are in the couple
of *hundred* bytes. Not kilobytes, and not megabytes.
The most performance-critical objects for uncompression are commits and
trees. At least for the kernel, the average size of a tree object is 678
bytes. And that's ignoring the fact that most of them are then deltified,
so about 80% of them are likely just a ~60-byte delta.
Linus
^ permalink raw reply [flat|nested] 79+ messages in thread
* Re: cleaner/better zlib sources?
2007-03-16 16:21 ` Linus Torvalds
@ 2007-03-16 16:24 ` Davide Libenzi
2007-03-16 16:35 ` Linus Torvalds
2007-03-16 16:35 ` cleaner/better zlib sources? Jeff Garzik
2007-03-16 17:06 ` Nicolas Pitre
2 siblings, 1 reply; 79+ messages in thread
From: Davide Libenzi @ 2007-03-16 16:24 UTC (permalink / raw)
To: Linus Torvalds; +Cc: Jeff Garzik, Git Mailing List, mpm, bcrl
On Fri, 16 Mar 2007, Linus Torvalds wrote:
> On Thu, 15 Mar 2007, Davide Libenzi wrote:
> >
> > Hacked up test case below ...
>
> This one seems to do benchmarking with 8MB buffers if I read it right
> (didn't try).
Yes, I just wanted to have the biggest time spent in inflate(). That why I
use a big buffer.
> The normal size for the performance-critical git objects are in the couple
> of *hundred* bytes. Not kilobytes, and not megabytes.
>
> The most performance-critical objects for uncompression are commits and
> trees. At least for the kernel, the average size of a tree object is 678
> bytes. And that's ignoring the fact that most of them are then deltified,
> so about 80% of them are likely just a ~60-byte delta.
Definitely. The nature of the data matters.
Did you try to make a zlib with my patch and oprofile git on real data
with that?
- Davide
^ permalink raw reply [flat|nested] 79+ messages in thread
* Re: cleaner/better zlib sources?
2007-03-16 16:21 ` Linus Torvalds
2007-03-16 16:24 ` Davide Libenzi
@ 2007-03-16 16:35 ` Jeff Garzik
2007-03-16 16:42 ` Matt Mackall
` (3 more replies)
2007-03-16 17:06 ` Nicolas Pitre
2 siblings, 4 replies; 79+ messages in thread
From: Jeff Garzik @ 2007-03-16 16:35 UTC (permalink / raw)
To: Linus Torvalds; +Cc: Davide Libenzi, Git Mailing List, mpm, bcrl
Linus Torvalds wrote:
> The normal size for the performance-critical git objects are in the couple
> of *hundred* bytes. Not kilobytes, and not megabytes.
>
> The most performance-critical objects for uncompression are commits and
> trees. At least for the kernel, the average size of a tree object is 678
> bytes. And that's ignoring the fact that most of them are then deltified,
> so about 80% of them are likely just a ~60-byte delta.
Ahhh. At least for me, that explains a lot. Rather than spending all
its time in inflate_fast(), git is dealing with lots of zlib
startup/shutdown overhead.
Although it sounds like zlib could indeed be optimized to reduce its
startup and shutdown overhead, I wonder if switching compression
algorithms to a pure Huffman or even RLE compression (with associated
lower startup/shutdown costs) would perform better in the face of all
those small objects.
And another random thought, though it may be useless in this thread: I
bet using a pre-built (compiled into git) static zlib dictionary for git
commit and tree objects might improve things a bit.
Jeff
^ permalink raw reply [flat|nested] 79+ messages in thread
* Re: cleaner/better zlib sources?
2007-03-16 16:24 ` Davide Libenzi
@ 2007-03-16 16:35 ` Linus Torvalds
2007-03-16 19:21 ` Davide Libenzi
0 siblings, 1 reply; 79+ messages in thread
From: Linus Torvalds @ 2007-03-16 16:35 UTC (permalink / raw)
To: Davide Libenzi; +Cc: Jeff Garzik, Git Mailing List, mpm, bcrl
On Fri, 16 Mar 2007, Davide Libenzi wrote:
>
> > This one seems to do benchmarking with 8MB buffers if I read it right
> > (didn't try).
>
> Yes, I just wanted to have the biggest time spent in inflate(). That why I
> use a big buffer.
Right. But if the biggest time is spent in setup, the big-buffer thing
ends up being exactly the wrong thing to test ;)
> Definitely. The nature of the data matters.
> Did you try to make a zlib with my patch and oprofile git on real data
> with that?
I haven't actually set it up so that I can build against my own zlib yet.
Exactly because I was hoping that somebody would already have a solution
;)
Will try to do later today, although since it's the kids school
conferences today I'll effectively be in and out all day long.
Linus
^ permalink raw reply [flat|nested] 79+ messages in thread
* Re: cleaner/better zlib sources?
2007-03-16 16:35 ` cleaner/better zlib sources? Jeff Garzik
@ 2007-03-16 16:42 ` Matt Mackall
2007-03-16 16:51 ` Linus Torvalds
` (2 subsequent siblings)
3 siblings, 0 replies; 79+ messages in thread
From: Matt Mackall @ 2007-03-16 16:42 UTC (permalink / raw)
To: Jeff Garzik; +Cc: Linus Torvalds, Davide Libenzi, Git Mailing List, bcrl
On Fri, Mar 16, 2007 at 12:35:39PM -0400, Jeff Garzik wrote:
> Linus Torvalds wrote:
> >The normal size for the performance-critical git objects are in the couple
> >of *hundred* bytes. Not kilobytes, and not megabytes.
> >
> >The most performance-critical objects for uncompression are commits and
> >trees. At least for the kernel, the average size of a tree object is 678
> >bytes. And that's ignoring the fact that most of them are then deltified,
> >so about 80% of them are likely just a ~60-byte delta.
>
>
> Ahhh. At least for me, that explains a lot. Rather than spending all
> its time in inflate_fast(), git is dealing with lots of zlib
> startup/shutdown overhead.
>
> Although it sounds like zlib could indeed be optimized to reduce its
> startup and shutdown overhead, I wonder if switching compression
> algorithms to a pure Huffman or even RLE compression (with associated
> lower startup/shutdown costs) would perform better in the face of all
> those small objects.
Mercurial simply stores uncompressed objects below a threshold of 44
bytes, based on benchmarks I did in April 2005. I'd probably up that
number if I redid my measurements today. There's just not a whole lot
zlib can do at these small sizes. Given that a SHA hash is an
uncompressible 20 bytes already, you're well into the domain of
diminishing returns.
> And another random thought, though it may be useless in this thread: I
> bet using a pre-built (compiled into git) static zlib dictionary for git
> commit and tree objects might improve things a bit.
Ideally, you'd compress all deltas in a chain with the same context.
You've got to decompress the delta base to do the delta
calculation, so this should allow you to recover the context up to
that point. Zlib isn't really set up for this sort of thing though.
--
Mathematics is the supreme nostalgia of our time.
^ permalink raw reply [flat|nested] 79+ messages in thread
* Re: cleaner/better zlib sources?
2007-03-16 16:35 ` cleaner/better zlib sources? Jeff Garzik
2007-03-16 16:42 ` Matt Mackall
@ 2007-03-16 16:51 ` Linus Torvalds
2007-03-16 17:12 ` Nicolas Pitre
2007-03-16 23:22 ` Shawn O. Pearce
3 siblings, 0 replies; 79+ messages in thread
From: Linus Torvalds @ 2007-03-16 16:51 UTC (permalink / raw)
To: Jeff Garzik; +Cc: Davide Libenzi, Git Mailing List, mpm, bcrl
On Fri, 16 Mar 2007, Jeff Garzik wrote:
>
> Although it sounds like zlib could indeed be optimized to reduce its startup
> and shutdown overhead, I wonder if switching compression algorithms to a pure
> Huffman or even RLE compression (with associated lower startup/shutdown costs)
> would perform better in the face of all those small objects.
Well, the thing is, I personally much prefer to have just a single
compression algorithm and object layout. Most of the performance-critical
objects from a decompression standpoint during commit traversal are all
small (especially if you do pathname limiting), but when you do something
like a "git add ." most objects are actually random blob objects and you
need to have a compression algorithm that works in the general case too.
Of course, pack-v4 may (likely will) end up using different strategies for
different objects (delta's in particular), but the "one single object
compression type" was a big deal for initial implementation.
It's may not be fundamental to git operation (so we can fairly easily
change it and make it more complex without any higher-level stuff even
noticing), but it was definitely fundamental to "get something stable and
working" up and running quickly..
> And another random thought, though it may be useless in this thread: I bet
> using a pre-built (compiled into git) static zlib dictionary for git commit
> and tree objects might improve things a bit.
That's kind of pack-v4 area. It will happen, but I'd actually like to see
if we can just avoid stupid performance problems with zlib, independently
of trying to make more tuned formats.
Linus
^ permalink raw reply [flat|nested] 79+ messages in thread
* Re: cleaner/better zlib sources?
2007-03-16 16:21 ` Linus Torvalds
2007-03-16 16:24 ` Davide Libenzi
2007-03-16 16:35 ` cleaner/better zlib sources? Jeff Garzik
@ 2007-03-16 17:06 ` Nicolas Pitre
2007-03-16 17:51 ` Linus Torvalds
2 siblings, 1 reply; 79+ messages in thread
From: Nicolas Pitre @ 2007-03-16 17:06 UTC (permalink / raw)
To: Linus Torvalds; +Cc: Davide Libenzi, Jeff Garzik, Git Mailing List, mpm, bcrl
On Fri, 16 Mar 2007, Linus Torvalds wrote:
> The most performance-critical objects for uncompression are commits and
> trees. At least for the kernel, the average size of a tree object is 678
> bytes. And that's ignoring the fact that most of them are then deltified,
> so about 80% of them are likely just a ~60-byte delta.
This is why in pack v4 there will be an alternate tree object
representation which is not deflated at all.
In short we intend to have 3 tables where common things are factored
out:
1) the path component string table (deflated)
2) author/committer string table (deflated)
3) sorted SHA1 table (obviously not deflated)
The sorted SHA1 table will be part of the pack instead of being in the
pack index. The idea is that most SHA1's are already duplicated in the
pack already anyway within commit and tree objects. With a single table
then commit and tree objects can index into that SHA1 table rather than
providing the SHA1 value inline for the objects they refer to.
This means that a tree object record would be only 6 bytes according to
the current design: 2 bytes to index into the path component string
table (which also include the mode information), and 4 bytes to index
into the sorted SHA1 table. And similarly for commit objects.
This means that the pack index will only have a table of offsets
corresponding to the table of sorted SHA1's.
So... walking revisions will become only a matter of picking the first
commit object, using the tree index value (which is not deflated), but
instead of using it in the SHA1 table it could be used in the offset
table to find the location of the corresponding tree object directly.
Same goes for tree entries, or for locating the parent's commit object.
No deflating, no binary searching, no SHA1 comparisons. Plain straight
pointer dereference.
Then, if you want to filter tree walking on path spec, you only need to
locate the path component in the path table once and use the
corresponding index to filter tree entries instead of repeated strcmp().
Same thing if you want to filter commits based on author/committer.
One side effect of this is that you can tell straight away that a path
doesn't exist in the whole pack if one of its components cannot be found
in the table (that works only if no legacy tree representations are
present of course). That should make history walking blazingly fast.
The only thing that gets deflated is the commit message which needs to
be inflated only when displaying it.
And so far that makes for quite smaller packs too!
Nicolas
^ permalink raw reply [flat|nested] 79+ messages in thread
* Re: cleaner/better zlib sources?
2007-03-16 16:35 ` cleaner/better zlib sources? Jeff Garzik
2007-03-16 16:42 ` Matt Mackall
2007-03-16 16:51 ` Linus Torvalds
@ 2007-03-16 17:12 ` Nicolas Pitre
2007-03-16 23:22 ` Shawn O. Pearce
3 siblings, 0 replies; 79+ messages in thread
From: Nicolas Pitre @ 2007-03-16 17:12 UTC (permalink / raw)
To: Jeff Garzik; +Cc: Linus Torvalds, Davide Libenzi, Git Mailing List, mpm, bcrl
On Fri, 16 Mar 2007, Jeff Garzik wrote:
> Although it sounds like zlib could indeed be optimized to reduce its startup
> and shutdown overhead, I wonder if switching compression algorithms to a pure
> Huffman or even RLE compression (with associated lower startup/shutdown costs)
> would perform better in the face of all those small objects.
>
> And another random thought, though it may be useless in this thread: I bet
> using a pre-built (compiled into git) static zlib dictionary for git commit
> and tree objects might improve things a bit.
See my last post. We'll do even better with special object
encoding altogether. Those representations are so dense that
compression provides no gain at all making the point moot.
Nicolas
^ permalink raw reply [flat|nested] 79+ messages in thread
* Re: cleaner/better zlib sources?
2007-03-16 17:06 ` Nicolas Pitre
@ 2007-03-16 17:51 ` Linus Torvalds
2007-03-16 18:09 ` Nicolas Pitre
0 siblings, 1 reply; 79+ messages in thread
From: Linus Torvalds @ 2007-03-16 17:51 UTC (permalink / raw)
To: Nicolas Pitre; +Cc: Davide Libenzi, Jeff Garzik, Git Mailing List, mpm, bcrl
On Fri, 16 Mar 2007, Nicolas Pitre wrote:
> On Fri, 16 Mar 2007, Linus Torvalds wrote:
>
> > The most performance-critical objects for uncompression are commits and
> > trees. At least for the kernel, the average size of a tree object is 678
> > bytes. And that's ignoring the fact that most of them are then deltified,
> > so about 80% of them are likely just a ~60-byte delta.
>
> This is why in pack v4 there will be an alternate tree object
> representation which is not deflated at all.
Well, the thing is, for things that really don't compress, zlib shouldn't
add much of an overhead on uncompression. It *should* just end up being a
single "memcpy()" after you've done:
- check the header for size and mode ("plain data")
- check the adler checksum (which is *really* nice - we've found real
corruption this way!).
The adler32 checksumming may sound unnecessary when you already have the
SHA1 checksum, but the thing is, we normally don't actually *check* the
SHA1 except when doing a full fsck. So I actually like the fact that
object unpacking always checks at least the adler32 checksum at each
stage, which you get "for free" when you use zlib.
So not using compression at all actually not only gets rid of the
compression, it gets rid of a good safety valve - something that may not
be immediately obvious when you don't think about what all zlib entails.
People think of zlib as just compressing, but I think the checksumming is
almost as important, which is why it isn't an obviously good thing to not
compress small objects just because you don't win on size!
Remember: stability and safety of the data is *the* #1 objective here. The
git SHA1 checksums guarantees that we can find any corruption, but in
every-day git usage, the adler32 checksum is the one that generally would
*notice* the corruption and cause us to say "uhhuh, need to fsck".
Everything else is totally secondary to the goal of "your data is secure".
Yes, performance is a primary goal too, but it's always "performance with
correctness guarantees"!
But I just traced through a simple 60-byte incompressible zlib thing. It's
painful. This should be *the* simplest case, and it should really just be
the memcpy and the adler32 check. But:
[torvalds@woody ~]$ grep '<inflate' trace | wc -l
460
[torvalds@woody ~]$ grep '<adler32' trace | wc -l
403
[torvalds@woody ~]$ grep '<memcpy' trace | wc -l
59
ie we spend *more* instructions on just the stupid setup in "inflate()"
than we spend on the adler32 (or, obviously, on the actual 60-byte memcpy
of the actual incompressible data)
I dunno. I don't mind the adler32 that much. The rest seems to be
pretty annoying, though.
Linus
^ permalink raw reply [flat|nested] 79+ messages in thread
* Re: cleaner/better zlib sources?
2007-03-16 17:51 ` Linus Torvalds
@ 2007-03-16 18:09 ` Nicolas Pitre
0 siblings, 0 replies; 79+ messages in thread
From: Nicolas Pitre @ 2007-03-16 18:09 UTC (permalink / raw)
To: Linus Torvalds; +Cc: Davide Libenzi, Jeff Garzik, Git Mailing List, mpm, bcrl
On Fri, 16 Mar 2007, Linus Torvalds wrote:
> On Fri, 16 Mar 2007, Nicolas Pitre wrote:
>
> > This is why in pack v4 there will be an alternate tree object
> > representation which is not deflated at all.
>
> Well, the thing is, for things that really don't compress, zlib shouldn't
> add much of an overhead on uncompression. It *should* just end up being a
> single "memcpy()" after you've done:
> - check the header for size and mode ("plain data")
> - check the adler checksum (which is *really* nice - we've found real
> corruption this way!).
But the thing is that with tree objects which records are 6 fairly
random bytes we already know that compression will never be worth it
size wise, so it is not worth it even if the header overhead was zero.
In that case it is preferable to do without compression entirely.
> The adler32 checksumming may sound unnecessary when you already have the
> SHA1 checksum, but the thing is, we normally don't actually *check* the
> SHA1 except when doing a full fsck. So I actually like the fact that
> object unpacking always checks at least the adler32 checksum at each
> stage, which you get "for free" when you use zlib.
We still can perform adler32 on undeflated objects directly though. But
they need no be stored in the pack. I'd store the adler32 checksum for
each object in the pack index as it can be recomputed by index-pack
(which will do the full SHA1 validation anyway).
Nicolas
^ permalink raw reply [flat|nested] 79+ messages in thread
* Re: cleaner/better zlib sources?
2007-03-16 16:35 ` Linus Torvalds
@ 2007-03-16 19:21 ` Davide Libenzi
2007-03-17 0:01 ` Linus Torvalds
0 siblings, 1 reply; 79+ messages in thread
From: Davide Libenzi @ 2007-03-16 19:21 UTC (permalink / raw)
To: Linus Torvalds; +Cc: Jeff Garzik, Git Mailing List, mpm, bcrl
On Fri, 16 Mar 2007, Linus Torvalds wrote:
>
>
> On Fri, 16 Mar 2007, Davide Libenzi wrote:
> >
> > > This one seems to do benchmarking with 8MB buffers if I read it right
> > > (didn't try).
> >
> > Yes, I just wanted to have the biggest time spent in inflate(). That why I
> > use a big buffer.
>
> Right. But if the biggest time is spent in setup, the big-buffer thing
> ends up being exactly the wrong thing to test ;)
I modified ztest.c to be able to bench on various data files (you list
them on the command line), but result are pretty much same.
I cannot measure any sensible difference between the two.
Attached there's ztest.c and the diff, in case you want to try on your
own.
> > Definitely. The nature of the data matters.
> > Did you try to make a zlib with my patch and oprofile git on real data
> > with that?
>
> I haven't actually set it up so that I can build against my own zlib yet.
> Exactly because I was hoping that somebody would already have a solution
> ;)
An LD_PRELOAD pointing to your own build should do it.
- Davide
#include <sys/types.h>
#include <sys/stat.h>
#include <sys/time.h>
#include <sys/mman.h>
#include <stdio.h>
#include <string.h>
#include <stdlib.h>
#include <fcntl.h>
#include <time.h>
#include "zlib.h"
#define MIN_TESTIME (2 * 1000000)
#define INNER_CYCLES 32
#define CHECK_ERR(err, msg) do { \
if (err != Z_OK) { \
fprintf(stderr, "%s error: %d\n", msg, err); \
exit(1); \
} \
} while (0)
static unsigned long long mintt = MIN_TESTIME;
static uLong incycles = INNER_CYCLES;
static unsigned long long getustime(void) {
struct timeval tm;
gettimeofday(&tm, NULL);
return tm.tv_sec * 1000000ULL + tm.tv_usec;
}
static void do_defl(Byte *cdata, uLong *clen,
Byte *udata, uLong uclen) {
z_stream c_stream; /* compression stream */
int err;
c_stream.zalloc = (alloc_func) NULL;
c_stream.zfree = (free_func) NULL;
c_stream.opaque = (voidpf) NULL;
err = deflateInit(&c_stream, Z_BEST_SPEED);
CHECK_ERR(err, "deflateInit");
c_stream.next_out = cdata;
c_stream.avail_out = (uInt) *clen;
/* At this point, udata is still mostly zeroes, so it should compress
* very well:
*/
c_stream.next_in = udata;
c_stream.avail_in = (uInt) uclen;
err = deflate(&c_stream, Z_FINISH);
if (err != Z_STREAM_END) {
fprintf(stderr, "whoops, got %d instead of Z_STREAM_END\n", err);
exit(1);
}
err = deflateEnd(&c_stream);
CHECK_ERR(err, "deflateEnd");
*clen = c_stream.next_out - cdata;
}
static void do_infl(Byte *cdata, uLong clen,
Byte *udata, uLong *uclen) {
int err;
z_stream d_stream; /* decompression stream */
d_stream.zalloc = (alloc_func) NULL;
d_stream.zfree = (free_func) NULL;
d_stream.opaque = (voidpf) NULL;
d_stream.next_in = cdata;
d_stream.avail_in = (uInt) clen;
err = inflateInit(&d_stream);
CHECK_ERR(err, "inflateInit");
d_stream.next_out = udata; /* discard the output */
d_stream.avail_out = (uInt) *uclen;
err = inflate(&d_stream, Z_FULL_FLUSH);
if (err != Z_STREAM_END) {
fprintf(stderr, "deflate should report Z_STREAM_END\n");
exit(1);
}
err = inflateEnd(&d_stream);
CHECK_ERR(err, "inflateEnd");
*uclen = d_stream.next_out - udata;
}
static int do_filebench(char const *fpath) {
int fd, err = -1;
uLong i, n, clen, ulen, size;
Byte *ubuf, *cbuf, *tbuf;
unsigned long long ts, te;
void *addr;
struct stat stb;
if ((fd = open(fpath, O_RDONLY)) == -1 ||
fstat(fd, &stb)) {
perror(fpath);
close(fd);
return -1;
}
size = stb.st_size;
addr = mmap(NULL, size, PROT_READ, MAP_PRIVATE, fd, 0);
close(fd);
if (addr == (void *) -1L) {
perror("mmap");
return -1;
}
ulen = size;
clen = size + 4096;
ubuf = addr;
if ((tbuf = malloc(ulen + clen)) == NULL) {
perror("malloc");
goto err_exit;
}
cbuf = tbuf + ulen;
/* Warming up ... */
do_defl(cbuf, &clen, ubuf, ulen);
do_infl(cbuf, clen, tbuf, &ulen);
if (ulen != size) {
fprintf(stderr, "size mismatch %lu instead of %lu\n",
(unsigned long) ulen, (unsigned long) size);
goto err_exit;
}
if (memcmp(tbuf, ubuf, size)) {
fprintf(stderr, "whoops! we did not get back the same data\n");
goto err_exit;
}
/* Test ... */
fprintf(stdout, "testing: %s\n", fpath);
ts = getustime();
n = 0;
do {
for (i = 0; i < incycles; i++) {
ulen = size;
do_infl(cbuf, clen, tbuf, &ulen);
}
n += i;
te = getustime();
} while (te - ts < mintt);
fprintf(stdout, "\tus time / cycle = %llu\n", (te - ts) / n);
err = 0;
err_exit:
free(tbuf);
munmap(addr, size);
return err;
}
int main(int ac, char **av) {
int i;
for (i = 1; i < ac; i++)
do_filebench(av[i]);
return 0;
}
Index: zlib-1.2.3.quilt/inflate.c
===================================================================
--- zlib-1.2.3.quilt.orig/inflate.c 2007-03-15 18:17:19.000000000 -0700
+++ zlib-1.2.3.quilt/inflate.c 2007-03-15 18:31:14.000000000 -0700
@@ -551,6 +551,15 @@
will return Z_BUF_ERROR if it has not reached the end of the stream.
*/
+#define CASE_DECL(n) \
+ case n: \
+ lbl_##n:
+
+#define STATE_CHANGE(s) do { \
+ state->mode = s; \
+ goto lbl_##s; \
+} while (0)
+
int ZEXPORT inflate(strm, flush)
z_streamp strm;
int flush;
@@ -586,10 +595,9 @@
ret = Z_OK;
for (;;)
switch (state->mode) {
- case HEAD:
+ CASE_DECL(HEAD)
if (state->wrap == 0) {
- state->mode = TYPEDO;
- break;
+ STATE_CHANGE(TYPEDO);
}
NEEDBITS(16);
#ifdef GUNZIP
@@ -597,8 +605,7 @@
state->check = crc32(0L, Z_NULL, 0);
CRC2(state->check, hold);
INITBITS();
- state->mode = FLAGS;
- break;
+ STATE_CHANGE(FLAGS);
}
state->flags = 0; /* expect zlib header */
if (state->head != Z_NULL)
@@ -609,20 +616,17 @@
#endif
((BITS(8) << 8) + (hold >> 8)) % 31) {
strm->msg = (char *)"incorrect header check";
- state->mode = BAD;
- break;
+ STATE_CHANGE(BAD);
}
if (BITS(4) != Z_DEFLATED) {
strm->msg = (char *)"unknown compression method";
- state->mode = BAD;
- break;
+ STATE_CHANGE(BAD);
}
DROPBITS(4);
len = BITS(4) + 8;
if (len > state->wbits) {
strm->msg = (char *)"invalid window size";
- state->mode = BAD;
- break;
+ STATE_CHANGE(BAD);
}
state->dmax = 1U << len;
Tracev((stderr, "inflate: zlib header ok\n"));
@@ -631,32 +635,30 @@
INITBITS();
break;
#ifdef GUNZIP
- case FLAGS:
+ CASE_DECL(FLAGS)
NEEDBITS(16);
state->flags = (int)(hold);
if ((state->flags & 0xff) != Z_DEFLATED) {
strm->msg = (char *)"unknown compression method";
- state->mode = BAD;
- break;
+ STATE_CHANGE(BAD);
}
if (state->flags & 0xe000) {
strm->msg = (char *)"unknown header flags set";
- state->mode = BAD;
- break;
+ STATE_CHANGE(BAD);
}
if (state->head != Z_NULL)
state->head->text = (int)((hold >> 8) & 1);
if (state->flags & 0x0200) CRC2(state->check, hold);
INITBITS();
state->mode = TIME;
- case TIME:
+ CASE_DECL(TIME)
NEEDBITS(32);
if (state->head != Z_NULL)
state->head->time = hold;
if (state->flags & 0x0200) CRC4(state->check, hold);
INITBITS();
state->mode = OS;
- case OS:
+ CASE_DECL(OS)
NEEDBITS(16);
if (state->head != Z_NULL) {
state->head->xflags = (int)(hold & 0xff);
@@ -665,7 +667,7 @@
if (state->flags & 0x0200) CRC2(state->check, hold);
INITBITS();
state->mode = EXLEN;
- case EXLEN:
+ CASE_DECL(EXLEN)
if (state->flags & 0x0400) {
NEEDBITS(16);
state->length = (unsigned)(hold);
@@ -677,7 +679,7 @@
else if (state->head != Z_NULL)
state->head->extra = Z_NULL;
state->mode = EXTRA;
- case EXTRA:
+ CASE_DECL(EXTRA)
if (state->flags & 0x0400) {
copy = state->length;
if (copy > have) copy = have;
@@ -699,7 +701,7 @@
}
state->length = 0;
state->mode = NAME;
- case NAME:
+ CASE_DECL(NAME)
if (state->flags & 0x0800) {
if (have == 0) goto inf_leave;
copy = 0;
@@ -720,7 +722,7 @@
state->head->name = Z_NULL;
state->length = 0;
state->mode = COMMENT;
- case COMMENT:
+ CASE_DECL(COMMENT)
if (state->flags & 0x1000) {
if (have == 0) goto inf_leave;
copy = 0;
@@ -740,13 +742,12 @@
else if (state->head != Z_NULL)
state->head->comment = Z_NULL;
state->mode = HCRC;
- case HCRC:
+ CASE_DECL(HCRC)
if (state->flags & 0x0200) {
NEEDBITS(16);
if (hold != (state->check & 0xffff)) {
strm->msg = (char *)"header crc mismatch";
- state->mode = BAD;
- break;
+ STATE_CHANGE(BAD);
}
INITBITS();
}
@@ -755,28 +756,26 @@
state->head->done = 1;
}
strm->adler = state->check = crc32(0L, Z_NULL, 0);
- state->mode = TYPE;
- break;
+ STATE_CHANGE(TYPE);
#endif
- case DICTID:
+ CASE_DECL(DICTID)
NEEDBITS(32);
strm->adler = state->check = REVERSE(hold);
INITBITS();
state->mode = DICT;
- case DICT:
+ CASE_DECL(DICT)
if (state->havedict == 0) {
RESTORE();
return Z_NEED_DICT;
}
strm->adler = state->check = adler32(0L, Z_NULL, 0);
state->mode = TYPE;
- case TYPE:
+ CASE_DECL(TYPE)
if (flush == Z_BLOCK) goto inf_leave;
- case TYPEDO:
+ CASE_DECL(TYPEDO)
if (state->last) {
BYTEBITS();
- state->mode = CHECK;
- break;
+ STATE_CHANGE(CHECK);
}
NEEDBITS(3);
state->last = BITS(1);
@@ -785,39 +784,38 @@
case 0: /* stored block */
Tracev((stderr, "inflate: stored block%s\n",
state->last ? " (last)" : ""));
- state->mode = STORED;
- break;
+ DROPBITS(2);
+ STATE_CHANGE(STORED);
case 1: /* fixed block */
fixedtables(state);
Tracev((stderr, "inflate: fixed codes block%s\n",
state->last ? " (last)" : ""));
- state->mode = LEN; /* decode codes */
- break;
+ DROPBITS(2);
+ STATE_CHANGE(LEN);
case 2: /* dynamic block */
Tracev((stderr, "inflate: dynamic codes block%s\n",
state->last ? " (last)" : ""));
- state->mode = TABLE;
- break;
+ DROPBITS(2);
+ STATE_CHANGE(TABLE);
case 3:
+ DROPBITS(2);
strm->msg = (char *)"invalid block type";
- state->mode = BAD;
+ STATE_CHANGE(BAD);
}
- DROPBITS(2);
break;
- case STORED:
+ CASE_DECL(STORED)
BYTEBITS(); /* go to byte boundary */
NEEDBITS(32);
if ((hold & 0xffff) != ((hold >> 16) ^ 0xffff)) {
strm->msg = (char *)"invalid stored block lengths";
- state->mode = BAD;
- break;
+ STATE_CHANGE(BAD);
}
state->length = (unsigned)hold & 0xffff;
Tracev((stderr, "inflate: stored length %u\n",
state->length));
INITBITS();
state->mode = COPY;
- case COPY:
+ CASE_DECL(COPY)
copy = state->length;
if (copy) {
if (copy > have) copy = have;
@@ -832,9 +830,8 @@
break;
}
Tracev((stderr, "inflate: stored end\n"));
- state->mode = TYPE;
- break;
- case TABLE:
+ STATE_CHANGE(TYPE);
+ CASE_DECL(TABLE)
NEEDBITS(14);
state->nlen = BITS(5) + 257;
DROPBITS(5);
@@ -845,14 +842,13 @@
#ifndef PKZIP_BUG_WORKAROUND
if (state->nlen > 286 || state->ndist > 30) {
strm->msg = (char *)"too many length or distance symbols";
- state->mode = BAD;
- break;
+ STATE_CHANGE(BAD);
}
#endif
Tracev((stderr, "inflate: table sizes ok\n"));
state->have = 0;
state->mode = LENLENS;
- case LENLENS:
+ CASE_DECL(LENLENS)
while (state->have < state->ncode) {
NEEDBITS(3);
state->lens[order[state->have++]] = (unsigned short)BITS(3);
@@ -867,13 +863,12 @@
&(state->lenbits), state->work);
if (ret) {
strm->msg = (char *)"invalid code lengths set";
- state->mode = BAD;
- break;
+ STATE_CHANGE(BAD);
}
Tracev((stderr, "inflate: code lengths ok\n"));
state->have = 0;
state->mode = CODELENS;
- case CODELENS:
+ CASE_DECL(CODELENS)
while (state->have < state->nlen + state->ndist) {
for (;;) {
this = state->lencode[BITS(state->lenbits)];
@@ -891,8 +886,7 @@
DROPBITS(this.bits);
if (state->have == 0) {
strm->msg = (char *)"invalid bit length repeat";
- state->mode = BAD;
- break;
+ STATE_CHANGE(BAD);
}
len = state->lens[state->have - 1];
copy = 3 + BITS(2);
@@ -914,17 +908,13 @@
}
if (state->have + copy > state->nlen + state->ndist) {
strm->msg = (char *)"invalid bit length repeat";
- state->mode = BAD;
- break;
+ STATE_CHANGE(BAD);
}
while (copy--)
state->lens[state->have++] = (unsigned short)len;
}
}
- /* handle error breaks in while */
- if (state->mode == BAD) break;
-
/* build code tables */
state->next = state->codes;
state->lencode = (code const FAR *)(state->next);
@@ -933,8 +923,7 @@
&(state->lenbits), state->work);
if (ret) {
strm->msg = (char *)"invalid literal/lengths set";
- state->mode = BAD;
- break;
+ STATE_CHANGE(BAD);
}
state->distcode = (code const FAR *)(state->next);
state->distbits = 6;
@@ -942,12 +931,11 @@
&(state->next), &(state->distbits), state->work);
if (ret) {
strm->msg = (char *)"invalid distances set";
- state->mode = BAD;
- break;
+ STATE_CHANGE(BAD);
}
Tracev((stderr, "inflate: codes ok\n"));
state->mode = LEN;
- case LEN:
+ CASE_DECL(LEN)
if (have >= 6 && left >= 258) {
RESTORE();
inflate_fast(strm, out);
@@ -975,22 +963,19 @@
Tracevv((stderr, this.val >= 0x20 && this.val < 0x7f ?
"inflate: literal '%c'\n" :
"inflate: literal 0x%02x\n", this.val));
- state->mode = LIT;
- break;
+ STATE_CHANGE(LIT);
}
if (this.op & 32) {
Tracevv((stderr, "inflate: end of block\n"));
- state->mode = TYPE;
- break;
+ STATE_CHANGE(TYPE);
}
if (this.op & 64) {
strm->msg = (char *)"invalid literal/length code";
- state->mode = BAD;
- break;
+ STATE_CHANGE(BAD);
}
state->extra = (unsigned)(this.op) & 15;
state->mode = LENEXT;
- case LENEXT:
+ CASE_DECL(LENEXT)
if (state->extra) {
NEEDBITS(state->extra);
state->length += BITS(state->extra);
@@ -998,7 +983,7 @@
}
Tracevv((stderr, "inflate: length %u\n", state->length));
state->mode = DIST;
- case DIST:
+ CASE_DECL(DIST)
for (;;) {
this = state->distcode[BITS(state->distbits)];
if ((unsigned)(this.bits) <= bits) break;
@@ -1017,13 +1002,12 @@
DROPBITS(this.bits);
if (this.op & 64) {
strm->msg = (char *)"invalid distance code";
- state->mode = BAD;
- break;
+ STATE_CHANGE(BAD);
}
state->offset = (unsigned)this.val;
state->extra = (unsigned)(this.op) & 15;
state->mode = DISTEXT;
- case DISTEXT:
+ CASE_DECL(DISTEXT)
if (state->extra) {
NEEDBITS(state->extra);
state->offset += BITS(state->extra);
@@ -1032,18 +1016,16 @@
#ifdef INFLATE_STRICT
if (state->offset > state->dmax) {
strm->msg = (char *)"invalid distance too far back";
- state->mode = BAD;
- break;
+ STATE_CHANGE(BAD);
}
#endif
if (state->offset > state->whave + out - left) {
strm->msg = (char *)"invalid distance too far back";
- state->mode = BAD;
- break;
+ STATE_CHANGE(BAD);
}
Tracevv((stderr, "inflate: distance %u\n", state->offset));
state->mode = MATCH;
- case MATCH:
+ CASE_DECL(MATCH)
if (left == 0) goto inf_leave;
copy = out - left;
if (state->offset > copy) { /* copy from window */
@@ -1066,15 +1048,15 @@
do {
*put++ = *from++;
} while (--copy);
- if (state->length == 0) state->mode = LEN;
+ if (state->length == 0)
+ STATE_CHANGE(LEN);
break;
- case LIT:
+ CASE_DECL(LIT)
if (left == 0) goto inf_leave;
*put++ = (unsigned char)(state->length);
left--;
- state->mode = LEN;
- break;
- case CHECK:
+ STATE_CHANGE(LEN);
+ CASE_DECL(CHECK)
if (state->wrap) {
NEEDBITS(32);
out -= left;
@@ -1090,36 +1072,34 @@
#endif
REVERSE(hold)) != state->check) {
strm->msg = (char *)"incorrect data check";
- state->mode = BAD;
- break;
+ STATE_CHANGE(BAD);
}
INITBITS();
Tracev((stderr, "inflate: check matches trailer\n"));
}
#ifdef GUNZIP
state->mode = LENGTH;
- case LENGTH:
+ CASE_DECL(LENGTH)
if (state->wrap && state->flags) {
NEEDBITS(32);
if (hold != (state->total & 0xffffffffUL)) {
strm->msg = (char *)"incorrect length check";
- state->mode = BAD;
- break;
+ STATE_CHANGE(BAD);
}
INITBITS();
Tracev((stderr, "inflate: length matches trailer\n"));
}
#endif
state->mode = DONE;
- case DONE:
+ CASE_DECL(DONE)
ret = Z_STREAM_END;
goto inf_leave;
- case BAD:
+ CASE_DECL(BAD)
ret = Z_DATA_ERROR;
goto inf_leave;
- case MEM:
+ CASE_DECL(MEM)
return Z_MEM_ERROR;
- case SYNC:
+ CASE_DECL(SYNC)
default:
return Z_STREAM_ERROR;
}
^ permalink raw reply [flat|nested] 79+ messages in thread
* Re: cleaner/better zlib sources?
2007-03-16 16:35 ` cleaner/better zlib sources? Jeff Garzik
` (2 preceding siblings ...)
2007-03-16 17:12 ` Nicolas Pitre
@ 2007-03-16 23:22 ` Shawn O. Pearce
3 siblings, 0 replies; 79+ messages in thread
From: Shawn O. Pearce @ 2007-03-16 23:22 UTC (permalink / raw)
To: Jeff Garzik; +Cc: Linus Torvalds, Davide Libenzi, Git Mailing List, mpm, bcrl
Jeff Garzik <jeff@garzik.org> wrote:
> Although it sounds like zlib could indeed be optimized to reduce its
> startup and shutdown overhead, I wonder if switching compression
> algorithms to a pure Huffman or even RLE compression (with associated
> lower startup/shutdown costs) would perform better in the face of all
> those small objects.
As Nico already stated, for pack v4 we are probably heading in a
direction where these really small (except for blobs anyway) objects
aren't compressed at all by zlib. They are smaller in disk space,
and are faster to reconstruct to their raw format.
> And another random thought, though it may be useless in this thread: I
> bet using a pre-built (compiled into git) static zlib dictionary for git
> commit and tree objects might improve things a bit.
I've actually tried this with the Mozilla project. The improvement
was under 2% on disk space usage and no runtime performance gains.
Not worth the pain involved. We are seeing much higher disk
space improvements and much better performance gains in the pack
v4 prototype.
Oh, and that was *with* a dictionary that was customized to Mozilla.
Not a static one. A lot of keywords in the dictionary were Mozilla
project specific, and would actually *hurt* compression for the
Linux kernel, Git, X.org, etc...
--
Shawn.
^ permalink raw reply [flat|nested] 79+ messages in thread
* Re: cleaner/better zlib sources?
2007-03-16 19:21 ` Davide Libenzi
@ 2007-03-17 0:01 ` Linus Torvalds
2007-03-17 1:11 ` Linus Torvalds
0 siblings, 1 reply; 79+ messages in thread
From: Linus Torvalds @ 2007-03-17 0:01 UTC (permalink / raw)
To: Davide Libenzi; +Cc: Jeff Garzik, Git Mailing List, mpm, bcrl
On Fri, 16 Mar 2007, Davide Libenzi wrote:
>
> I cannot measure any sensible difference between the two.
I'm using your previous patch (is it the same?) along with the additional
patch appended.
And yes, it's not hugely faster, but I seem to see *some* difference: this
is the real-time of ten runs of
time git log drivers/usb/ > /dev/null
Before:
0m2.673s
0m2.476s
0m2.603s
0m2.576s
0m2.625s
0m2.628s
0m2.493s
0m2.696s
0m2.525s
0m2.575s
After:
0m2.639s
0m2.519s
0m2.454s
0m2.604s
0m2.499s
0m2.497s
0m2.506s
0m2.394s
0m2.409s
0m2.562s
ie after I actually get under 2.4s once, and under 2.5s most of the time,
while before it was under 2.5s just twice, and mostly in the 2.6s..
(I did end up adding the "-g", but I trust that doesn't make things
*faster*. Generally gcc is good at not actually changing code generation
based on -g)
But yeah, not very impressive changes. We're talking *maybe* 0.1s out of
2.5, so potentially about 4% of total time but more likely about 2-3%, and
it's clearly mostly in the noise. And inflate() is still at 16%, and
inflate_fast obviously got no faster.
The nice part is that the instruction-level profile for inflate() got more
interesting. Instead of clearly peaking at the silly indirect jump, the
peak now seems to be a specific path through the thing. I've not decoded
it fully yet, but it seems to be mostly the LEN/LIT cases:
file inflate.c, line 942.
file inflate.c, line 942.
file inflate.c, line 949.
file inflate.c, line 949.
file inflate.c, line 949.
file inflate.c, line 949.
file inflate.c, line 949.
file inflate.c, line 950.
file inflate.c, line 950.
file inflate.c, line 951.
file inflate.c, line 951.
file inflate.c, line 951.
file inflate.c, line 951.
file inflate.c, line 951.
file inflate.c, line 949.
file inflate.c, line 949.
file inflate.c, line 950.
file inflate.c, line 950.
file inflate.c, line 953.
file inflate.c, line 953.
file inflate.c, line 953.
file inflate.c, line 969.
file inflate.c, line 1058.
file inflate.c, line 1059.
file inflate.c, line 1061.
file inflate.c, line 884.
file inflate.c, line 963.
file inflate.c, line 964.
(those are the line numbers *after* applying my patch for where the
hotpoints are: the same line-number showing up multiple times is just
because several hot instructions came from there and got spread out)
Linus
---
diff --git a/Makefile b/Makefile
index 2fd6e45..d8e9ff4 100644
--- a/Makefile
+++ b/Makefile
@@ -18,7 +18,7 @@
CC=cc
-CFLAGS=-O
+CFLAGS=-O -g
#CFLAGS=-O -DMAX_WBITS=14 -DMAX_MEM_LEVEL=7
#CFLAGS=-g -DDEBUG
#CFLAGS=-O3 -Wall -Wwrite-strings -Wpointer-arith -Wconversion \
diff --git a/inflate.c b/inflate.c
index 190c642..3d41d6f 100644
--- a/inflate.c
+++ b/inflate.c
@@ -568,7 +568,7 @@ int flush;
unsigned char FAR *next; /* next input */
unsigned char FAR *put; /* next output */
unsigned have, left; /* available input and output */
- unsigned long hold; /* bit buffer */
+ unsigned long hold, old_hold;/* bit buffer */
unsigned bits; /* bits in bit buffer */
unsigned in, out; /* save starting available input and output */
unsigned copy; /* number of stored or match bytes to copy */
@@ -631,8 +631,11 @@ int flush;
state->dmax = 1U << len;
Tracev((stderr, "inflate: zlib header ok\n"));
strm->adler = state->check = adler32(0L, Z_NULL, 0);
- state->mode = hold & 0x200 ? DICTID : TYPE;
+ old_hold = hold;
INITBITS();
+ if (old_hold & 0x200)
+ STATE_CHANGE(DICTID);
+ STATE_CHANGE(TYPE);
break;
#ifdef GUNZIP
CASE_DECL(FLAGS)
@@ -817,7 +820,7 @@ int flush;
state->mode = COPY;
CASE_DECL(COPY)
copy = state->length;
- if (copy) {
+ while (copy) {
if (copy > have) copy = have;
if (copy > left) copy = left;
if (copy == 0) goto inf_leave;
@@ -826,8 +829,8 @@ int flush;
next += copy;
left -= copy;
put += copy;
- state->length -= copy;
- break;
+ copy = state->length - copy;
+ state->length = copy;
}
Tracev((stderr, "inflate: stored end\n"));
STATE_CHANGE(TYPE);
^ permalink raw reply related [flat|nested] 79+ messages in thread
* Re: cleaner/better zlib sources?
2007-03-17 0:01 ` Linus Torvalds
@ 2007-03-17 1:11 ` Linus Torvalds
2007-03-17 3:28 ` Nicolas Pitre
0 siblings, 1 reply; 79+ messages in thread
From: Linus Torvalds @ 2007-03-17 1:11 UTC (permalink / raw)
To: Git Mailing List
[-- Attachment #1: Type: TEXT/PLAIN, Size: 4206 bytes --]
On Fri, 16 Mar 2007, Linus Torvalds wrote:
>
> And yes, it's not hugely faster, but I seem to see *some* difference: this
> is the real-time of ten runs of
>
> time git log drivers/usb/ > /dev/null
Damn. I think I know why it's happening, and I'm an idiot. I think it's
actually an issue I wondered about a *loong* time ago, and then forgot all
about. And later or Nico made it almost impossible to fix with his "pack
offset" changes.
The thing that made me realize was one of the callchains into inflate()
that I looked at:
(gdb) where
#0 inflate (strm=0x7fff10d83810, flush=4) at inflate.c:566
#1 0x000000000044c165 in unpack_compressed_entry (p=0x6d52e0, w_curs=0x7fff10d838e0, curpos=94941911,
size=<value optimized out>) at sha1_file.c:1348
#2 0x000000000044c2b6 in unpack_entry (p=0x6d52e0, obj_offset=94941909, type=0x7fff10d85d8c, sizep=0x7fff10d83928)
at sha1_file.c:1408
#3 0x000000000044c32e in unpack_entry (p=0x6d52e0, obj_offset=94942707, type=0x7fff10d85d8c, sizep=0x7fff10d83988)
at sha1_file.c:1373
#4 0x000000000044c32e in unpack_entry (p=0x6d52e0, obj_offset=94943021, type=0x7fff10d85d8c, sizep=0x7fff10d839e8)
at sha1_file.c:1373
#5 0x000000000044c32e in unpack_entry (p=0x6d52e0, obj_offset=94943382, type=0x7fff10d85d8c, sizep=0x7fff10d83a48)
at sha1_file.c:1373
#6 0x000000000044c32e in unpack_entry (p=0x6d52e0, obj_offset=94943531, type=0x7fff10d85d8c, sizep=0x7fff10d83aa8)
at sha1_file.c:1373
#7 0x000000000044c32e in unpack_entry (p=0x6d52e0, obj_offset=94943622, type=0x7fff10d85d8c, sizep=0x7fff10d83b08)
at sha1_file.c:1373
#8 0x000000000044c32e in unpack_entry (p=0x6d52e0, obj_offset=94945357, type=0x7fff10d85d8c, sizep=0x7fff10d83b68)
at sha1_file.c:1373
#9 0x000000000044c32e in unpack_entry (p=0x6d52e0, obj_offset=94945447, type=0x7fff10d85d8c, sizep=0x7fff10d83bc8)
at sha1_file.c:1373
#10 0x000000000044c32e in unpack_entry (p=0x6d52e0, obj_offset=94945571, type=0x7fff10d85d8c, sizep=0x7fff10d85d80)
at sha1_file.c:1373
#11 0x000000000044c3f8 in read_packed_sha1 (sha1=<value optimized out>, type=0x7fff10d85d8c, size=0x7fff10d85d80)
at sha1_file.c:1567
#12 0x000000000044c741 in read_sha1_file (sha1=0x7fff10d85d60 "�Ab\217��236���031", type=0x7fff10d85d8c,
size=0x7fff10d85d80) at sha1_file.c:1636
....
and notice the deep recursion in sha1_file.
The way we unpack delta chains is that we do
- find a delta
- we apply it to "recursively unpack the thing it's a delta to"
which sounds totally obvious and straightforward, right?
EXCEPT it's actually O(n**2) in the delta depth, because we never save the
intermediate results, so when we have a delta depth of 10 (our default),
and we decode a lot of these things, we basically will look up the base
object 10 times, apply the first delta 9 times, apply the second delta 8
times, etc etc..
I didn't worry about it, because it never actually hit as much of a
performance problem (and when you do a *single* tree operation you'd
never see it anyway: you apply the deltas you need, and nothing else),
but what it means is that we actually call inflate on the chain entries
55 times instead of just doing it 10 times.
It's also somewhat limited by the delta depth that we enforce anyway (I
say "somewhat", because we only limit the maximum depth, not the number of
times an object can be used as a base, and if you use an object as a base
a thousand times, it will literally be unpacked a thousand times too!
I also didn't worry about it, because I felt that if it became a problem,
it would be easy to just add a cache of base objects (we probably do *not*
want to keep the whole unpacked object info in memory all the time just
because of memory pressure issues, so "cache of base objects" is better).
However, the "pack file + offset" thing makes it harder to do, since we
now don't even have the SHA1 of the base object before we unpack it.
But I guess we could just index this by a <packfile, offset> tuple.
Anyway, I bet that this is a much bigger issue than the pack format
itself (and is largely independent).
Linus
^ permalink raw reply [flat|nested] 79+ messages in thread
* Re: cleaner/better zlib sources?
2007-03-17 1:11 ` Linus Torvalds
@ 2007-03-17 3:28 ` Nicolas Pitre
2007-03-17 5:19 ` Shawn O. Pearce
2007-03-17 17:55 ` Linus Torvalds
0 siblings, 2 replies; 79+ messages in thread
From: Nicolas Pitre @ 2007-03-17 3:28 UTC (permalink / raw)
To: Linus Torvalds; +Cc: Git Mailing List
On Fri, 16 Mar 2007, Linus Torvalds wrote:
> The way we unpack delta chains is that we do
>
> - find a delta
> - we apply it to "recursively unpack the thing it's a delta to"
>
> which sounds totally obvious and straightforward, right?
>
> EXCEPT it's actually O(n**2) in the delta depth, because we never save the
> intermediate results, so when we have a delta depth of 10 (our default),
> and we decode a lot of these things, we basically will look up the base
> object 10 times, apply the first delta 9 times, apply the second delta 8
> times, etc etc..
In the worst case, yes. And if you're walking history then the
probability of hitting the worst case eventually is rather high.
> I also didn't worry about it, because I felt that if it became a problem,
> it would be easy to just add a cache of base objects (we probably do *not*
> want to keep the whole unpacked object info in memory all the time just
> because of memory pressure issues, so "cache of base objects" is better).
> However, the "pack file + offset" thing makes it harder to do, since we
> now don't even have the SHA1 of the base object before we unpack it.
>
> But I guess we could just index this by a <packfile, offset> tuple.
Right. Should be really trivial to hook into unpack_delta_entry()
actually replacing the call to unpack_entry() with a wrapper function
that returns cached data, or populates the cache with unpack_entry()
when no match is found.
Then it would only be a matter of coming up with a clever cache
eviction algorithm.
> Anyway, I bet that this is a much bigger issue than the pack format
> itself (and is largely independent).
Well, I think the pack format issue is significant too. But because
those are independent issues the gain in performance will be additive.
Nicolas
^ permalink raw reply [flat|nested] 79+ messages in thread
* Re: cleaner/better zlib sources?
2007-03-17 3:28 ` Nicolas Pitre
@ 2007-03-17 5:19 ` Shawn O. Pearce
2007-03-17 17:55 ` Linus Torvalds
1 sibling, 0 replies; 79+ messages in thread
From: Shawn O. Pearce @ 2007-03-17 5:19 UTC (permalink / raw)
To: Nicolas Pitre; +Cc: Linus Torvalds, Git Mailing List
Nicolas Pitre <nico@cam.org> wrote:
> On Fri, 16 Mar 2007, Linus Torvalds wrote:
> > I also didn't worry about it, because I felt that if it became a problem,
> > it would be easy to just add a cache of base objects (we probably do *not*
> > want to keep the whole unpacked object info in memory all the time just
> > because of memory pressure issues, so "cache of base objects" is better).
> > However, the "pack file + offset" thing makes it harder to do, since we
> > now don't even have the SHA1 of the base object before we unpack it.
> >
> > But I guess we could just index this by a <packfile, offset> tuple.
...
> Then it would only be a matter of coming up with a clever cache
> eviction algorithm.
Yes. Linus above seems to imply (at least to me) that we wouldn't
want to cache the original object requested by read_sha1_file(), as
its not the delta base. But given our packing rules, we should be
(in general anyway) first asking for the most recent revision of
a file, which is stored whole, then for an older revision, which
will be a delta of the more recent revision we just saw.
Hence we probably would want to cache an object. Well, at least
anything that had been packed as a delta. Caching a deflated
OBJ_BLOB may not be worth it.
> > Anyway, I bet that this is a much bigger issue than the pack format
> > itself (and is largely independent).
>
> Well, I think the pack format issue is significant too. But because
> those are independent issues the gain in performance will be additive.
I'm torn there.
There's two places that we do lots of unpacks of objects where we
run into this difficult case of unpacking the same base object many
times: git-blame and a rev-list with a path limiter.
Now the git-blame case is obvious: we are constantly unpacking
various revisions of the same file, and these are probably delta'd
against each other, so the unpacking gets really brutal after a
while. A blob cache here would probably *really* help out git-blame.
What's slightly less obvious about git-blame is we are probably also
traversing the different versions of the same trees over and over, as
we resolve the path to the correct blob in each commit we traverse.
So again here we are hitting lots of the same trees multiple times.
That last part about git-blame also obviously applies to the rev-list
with a path limiter.
But most other operations don't seem like they would benefit from a
base object cache; actually they might slow down from having such
a cache present!
Commits tend not to delta well; if they delta it is a very rare
occurrance. So we aren't getting huge unpacking benefits there
by caching them. Scratch any benefit of the cache for any sort of
rev-list operation that doesn't require tree access.
As for the other common operations (diff, read-tree, checkout-index,
merge-recursive): I don't think these will benefit from a cache
either. Their data access patterns are pretty spread out over
the tree. With the exception of rename detection we hit everything
only once. After touching a path, we tend to not go back to it.
So unless we are really lucky and one blob acts as a base object
for many others at different paths (possible, but I suspect not
very likely) its not worth caching the base.
If we do hit something twice, its probably because we are doing two
distinct passes over the data. In this case the passes are probably
because we either don't want to hold all of the data in memory (too
big of a set for some projects) or because we tried one algorithm,
failed, and are now trying a different one (internal read-tree
in merge-recursive).
Caching in merge-recursive may help, but just making the dirty
cache (index) that resulted from the internal read-tree available
for the remainder of the merge-recursive process might be faster;
especially if we only have one base and don't need to recursively
merge multiple bases.
So where does that leave us? The only places I see a base object
cache really helping is in git-blame for blob access, repeated
tree access (git-blame and path limiting), and maybe we could do
better with the common cases in merge-recursive by being smarter
with the cache.
But with pack v4 I don't think I need a tree object cache.
With a 6 byte fixed record format, a strict ordering requirement,
a finite delta depth within a packfile, a stricter tree-specific
delta encoder, and a minor API change to tree-walk.h, I think we
can unpack the delta at the same time that we are walking the tree.
No upfront unpack required. Hence no reason to cache.
So yea, a base object cache may help us today. It will most
definately help in git-blame. But I doubt it will help with trees
in pack v4, and I think it will just hurt in most cases. So maybe
it should be local to git-blame only.
--
Shawn.
^ permalink raw reply [flat|nested] 79+ messages in thread
* Re: cleaner/better zlib sources?
2007-03-17 3:28 ` Nicolas Pitre
2007-03-17 5:19 ` Shawn O. Pearce
@ 2007-03-17 17:55 ` Linus Torvalds
2007-03-17 19:40 ` Linus Torvalds
1 sibling, 1 reply; 79+ messages in thread
From: Linus Torvalds @ 2007-03-17 17:55 UTC (permalink / raw)
To: Nicolas Pitre; +Cc: Git Mailing List
On Fri, 16 Mar 2007, Nicolas Pitre wrote:
>
> In the worst case, yes. And if you're walking history then the
> probability of hitting the worst case eventually is rather high.
Actually, it's even better than that.
If we're walking a certain pathspec (which is reall ythe only thing that
is expensive), we're pretty much *guaranteed* that we'll hit exactly this
case. Doing some instrumentation on the test-case I've been using (which
is just "git log drivers/usb/ > /dev/null") shows:
[torvalds@woody linux]$ grep Needs delta-base-trace | wc -l
469334
[torvalds@woody linux]$ grep Needs delta-base-trace | sort -u | wc -l
21933
where that delta-base-trace is just a trace of which delta bases were
needed. Look how we currently generate almost half a million of them, but
only 22000 are actually unique objects - we just generate many of them
over and over again. In fact, the top delta bases with counts looks like:
558 Needs 102398354
556 Needs 161353360
554 Needs 161354852
552 Needs 161354916
550 Needs 161354980
526 Needs 161355044
524 Needs 161355108
522 Needs 161355174
520 Needs 161355238
508 Needs 161445724
446 Needs 119712387
425 Needs 133406737
420 Needs 161513997
387 Needs 120784913
331 Needs 127094253
321 Needs 95694853
319 Needs 125888524
303 Needs 155109487
301 Needs 155627964
299 Needs 155628028
.....
ie the top twenty objects were all generated hundreds of times each.
More importantly, the trace also shows that it actually has very good
locality too - exactly as you'd expect, since when we traverse the trees,
we'd generally see a particular delta base used as a base when that thing
is slowly changing, so of the half-million "needs" entries in my trace, if
I pick the top delta_base (102398354), and use "cat -n" to give them all
line numbers (from 1 to half a million), and grep for that particular
delta:
grep Needs delta-base-trace | cat -n | grep 102398354 | less -S
they are *all* at lines 61624..89352, with the bulk of them being very
close together (the bulk of those are all around 88k line mark).
In other words, it's not "spread out" over time. It's very clustered,
which I'd expect anyway, which means that even a simple cache of just a
few hundred entries (statically sized) will be very effective.
So the cache doesn't need to be "complete". It will get good hit-rates
even from being very simple. I think I have a very simple and cunning
plan, I'll try it out asap.
Linus
^ permalink raw reply [flat|nested] 79+ messages in thread
* Re: cleaner/better zlib sources?
2007-03-17 17:55 ` Linus Torvalds
@ 2007-03-17 19:40 ` Linus Torvalds
2007-03-17 19:42 ` [PATCH 1/2] Make trivial wrapper functions around delta base generation and freeing Linus Torvalds
2007-03-17 19:44 ` [PATCH 2/2] Implement a simple delta_base cache Linus Torvalds
0 siblings, 2 replies; 79+ messages in thread
From: Linus Torvalds @ 2007-03-17 19:40 UTC (permalink / raw)
To: Nicolas Pitre; +Cc: Git Mailing List
On Sat, 17 Mar 2007, Linus Torvalds wrote:
>
> So the cache doesn't need to be "complete". It will get good hit-rates
> even from being very simple. I think I have a very simple and cunning
> plan, I'll try it out asap.
Ok, got distracted by guests coming to look at the new puppy, so it took
longer than it should have, but the following is a simple two-patch series
that improves path-following by a factor of almost 2.5 for me.
The cache is *really* simple. It's just a 256-entry hashed cache of the
last few base entries, and it brings down my test-case of
git log drivers/usb/ > /dev/null
from 2.5s to just over 1s. I have *not* tuned or tweaked this at all, and
maybe there are better ways to do this, but this was simple as hell and
obviously quite effective.
It also speeds up "git blame", for all the same reasons. Before (best
times out of a run of five):
[torvalds@woody linux]$ time git blame drivers/char/Makefile > /dev/null
real 0m1.585s
user 0m1.576s
sys 0m0.004s
after:
[torvalds@woody linux]$ time ~/git/git blame drivers/char/Makefile > /dev/null
real 0m0.763s
user 0m0.644s
sys 0m0.120s
so it's a factor of two there too (just a random file, I'm not at all
going to guarantee that this is really consistent - it should get more
testing etc).
The first patch just does some obvious re-factoring and setting up (no
real code changes). The second patch just uses the new functions to
actually add a cache.
Linus
^ permalink raw reply [flat|nested] 79+ messages in thread
* [PATCH 1/2] Make trivial wrapper functions around delta base generation and freeing
2007-03-17 19:40 ` Linus Torvalds
@ 2007-03-17 19:42 ` Linus Torvalds
2007-03-17 19:44 ` [PATCH 2/2] Implement a simple delta_base cache Linus Torvalds
1 sibling, 0 replies; 79+ messages in thread
From: Linus Torvalds @ 2007-03-17 19:42 UTC (permalink / raw)
To: Junio C Hamano, Nicolas Pitre; +Cc: Git Mailing List
This doesn't change any code, it just creates a point for where we'd
actually do the caching of delta bases that have been generated.
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
---
Done this way to make all the changes as obvious as possible.
diff --git a/sha1_file.c b/sha1_file.c
index 110d696..f11ca3f 100644
--- a/sha1_file.c
+++ b/sha1_file.c
@@ -1352,6 +1352,18 @@ static void *unpack_compressed_entry(struct packed_git *p,
return buffer;
}
+static void *cache_or_unpack_entry(struct packed_git *p, off_t base_offset,
+ unsigned long *base_size, enum object_type *type)
+{
+ return unpack_entry(p, base_offset, type, base_size);
+}
+
+static void add_delta_base_cache(struct packed_git *p, off_t base_offset,
+ void *base, unsigned long base_size, enum object_type type)
+{
+ free(base);
+}
+
static void *unpack_delta_entry(struct packed_git *p,
struct pack_window **w_curs,
off_t curpos,
@@ -1365,7 +1377,7 @@ static void *unpack_delta_entry(struct packed_git *p,
off_t base_offset;
base_offset = get_delta_base(p, w_curs, &curpos, *type, obj_offset);
- base = unpack_entry(p, base_offset, type, &base_size);
+ base = cache_or_unpack_entry(p, base_offset, &base_size, type);
if (!base)
die("failed to read delta base object"
" at %"PRIuMAX" from %s",
@@ -1378,7 +1390,7 @@ static void *unpack_delta_entry(struct packed_git *p,
if (!result)
die("failed to apply delta");
free(delta_data);
- free(base);
+ add_delta_base_cache(p, base_offset, base, base_size, *type);
return result;
}
^ permalink raw reply related [flat|nested] 79+ messages in thread
* [PATCH 2/2] Implement a simple delta_base cache
2007-03-17 19:40 ` Linus Torvalds
2007-03-17 19:42 ` [PATCH 1/2] Make trivial wrapper functions around delta base generation and freeing Linus Torvalds
@ 2007-03-17 19:44 ` Linus Torvalds
2007-03-17 21:45 ` Linus Torvalds
2007-03-17 22:44 ` Linus Torvalds
1 sibling, 2 replies; 79+ messages in thread
From: Linus Torvalds @ 2007-03-17 19:44 UTC (permalink / raw)
To: Junio C Hamano, Nicolas Pitre; +Cc: Git Mailing List
This trivial 256-entry delta_base cache improves performance for some
loads by a factor of 2.5 or so.
Instead of always re-generating the delta bases (possibly over and over
and over again), just cache the last few ones. They often can get re-used.
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
---
This should have some other people doing performance testing too, since
it's fairly core. But *dang*, it's really simple.
diff --git a/sha1_file.c b/sha1_file.c
index f11ca3f..a7e3a2a 100644
--- a/sha1_file.c
+++ b/sha1_file.c
@@ -1352,16 +1352,57 @@ static void *unpack_compressed_entry(struct packed_git *p,
return buffer;
}
+#define MAX_DELTA_CACHE (256)
+
+static struct delta_base_cache_entry {
+ struct packed_git *p;
+ off_t base_offset;
+ unsigned long size;
+ void *data;
+ enum object_type type;
+} delta_base_cache[MAX_DELTA_CACHE];
+
+static unsigned long pack_entry_hash(struct packed_git *p, off_t base_offset)
+{
+ unsigned long hash;
+
+ hash = (unsigned long)p + (unsigned long)base_offset;
+ hash += (hash >> 8) + (hash >> 16);
+ return hash & 0xff;
+}
+
static void *cache_or_unpack_entry(struct packed_git *p, off_t base_offset,
unsigned long *base_size, enum object_type *type)
{
+ void *ret;
+ unsigned long hash = pack_entry_hash(p, base_offset);
+ struct delta_base_cache_entry *ent = delta_base_cache + hash;
+
+ ret = ent->data;
+ if (ret && ent->p == p && ent->base_offset == base_offset)
+ goto found_cache_entry;
return unpack_entry(p, base_offset, type, base_size);
+
+found_cache_entry:
+ ent->data = NULL;
+ *type = ent->type;
+ *base_size = ent->size;
+ return ret;
}
static void add_delta_base_cache(struct packed_git *p, off_t base_offset,
void *base, unsigned long base_size, enum object_type type)
{
- free(base);
+ unsigned long hash = pack_entry_hash(p, base_offset);
+ struct delta_base_cache_entry *ent = delta_base_cache + hash;
+
+ if (ent->data)
+ free(ent->data);
+ ent->p = p;
+ ent->base_offset = base_offset;
+ ent->type = type;
+ ent->data = base;
+ ent->size = base_size;
}
static void *unpack_delta_entry(struct packed_git *p,
^ permalink raw reply related [flat|nested] 79+ messages in thread
* Re: [PATCH 2/2] Implement a simple delta_base cache
2007-03-17 19:44 ` [PATCH 2/2] Implement a simple delta_base cache Linus Torvalds
@ 2007-03-17 21:45 ` Linus Torvalds
2007-03-17 22:37 ` Junio C Hamano
` (2 more replies)
2007-03-17 22:44 ` Linus Torvalds
1 sibling, 3 replies; 79+ messages in thread
From: Linus Torvalds @ 2007-03-17 21:45 UTC (permalink / raw)
To: Junio C Hamano, Nicolas Pitre; +Cc: Git Mailing List
On Sat, 17 Mar 2007, Linus Torvalds wrote:
>
> Instead of always re-generating the delta bases (possibly over and over
> and over again), just cache the last few ones. They often can get re-used.
Not just to compare actual timings, this shows the difference in the
traces I did. Remember, before we had:
[torvalds@woody linux]$ grep Needs delta-base-trace | wc -l
469334
[torvalds@woody linux]$ grep Needs delta-base-trace |sort -u | wc -l
21933
and now with the simple cache, I get:
[torvalds@woody linux]$ grep Needs delta-base-trace-new | wc -l
28688
[torvalds@woody linux]$ grep Needs delta-base-trace-new | sort -u | wc -l
21933
ie, we still re-generate some of the objects multiple times, but now,
rather than generating them (on average) 20+ times each, we now generate
them an average of just 1.3 times each. Which explains why the wall-time
goes down by over a factor of two.
Changing the (statically sized) cache from 256 entries to 1024 (and
updating the hash function appropriately of course) gets the number down
to 23953 delta-base lookups (the number of unique ones obviously stays the
same), for an average of just 1.1 object generates per unique object, and
also means that you occasionally get sub-second times for my test-case of
logging drivers/usb/.
It all also means that libz isn't really even the top entry in the
profiles any more, although it's still pretty high. But the profile now
says:
samples % app name symbol name
41527 15.6550 git strlen
30215 11.3905 git inflate
27504 10.3685 git inflate_table
20321 7.6607 git find_pack_entry_one
16892 6.3680 git interesting
16259 6.1294 vmlinux __copy_user_nocache
16010 6.0355 git inflate_fast
9240 3.4833 git get_mode
8863 3.3412 git tree_entry_extract
7145 2.6935 git strncmp
7131 2.6883 git memcpy
6863 2.5872 git diff_tree
6113 2.3045 git adler32
4515 1.7021 git _int_malloc
3022 1.1392 git update_tree_entry
...
(Adding up all of libz is still ~31%, but it's lower as a percentage *and*
it's obviously a smaller percentage of a much lower absolute time, so the
zlib overhead went down much more than any other git overheads did)
In general, this all seems very cool. The patches are simple enough that I
think this is very safe to merge indeed: the only question I have is that
somebody should verify that the "struct packed_git *p" is stable over the
whole lifetime of a process - so that we can use it as a hash key without
having to invalidate hashes if we unmap a pack (I *think* we just unmap
the virtual mapping, and "struct packed_git *" stays valid, but Junio
should ack that for me).
Here's the trivial patch to extend the caching to 1k entries if somebody
cares. I don't know if the small added performance is worth it.
Linus
---
diff --git a/sha1_file.c b/sha1_file.c
index a7e3a2a..372af60 100644
--- a/sha1_file.c
+++ b/sha1_file.c
@@ -1352,7 +1352,7 @@ static void *unpack_compressed_entry(struct packed_git *p,
return buffer;
}
-#define MAX_DELTA_CACHE (256)
+#define MAX_DELTA_CACHE (1024)
static struct delta_base_cache_entry {
struct packed_git *p;
@@ -1367,8 +1367,8 @@ static unsigned long pack_entry_hash(struct packed_git *p, off_t base_offset)
unsigned long hash;
hash = (unsigned long)p + (unsigned long)base_offset;
- hash += (hash >> 8) + (hash >> 16);
- return hash & 0xff;
+ hash += (hash >> 10) + (hash >> 20);
+ return hash & (MAX_DELTA_CACHE-1);
}
static void *cache_or_unpack_entry(struct packed_git *p, off_t base_offset,
^ permalink raw reply related [flat|nested] 79+ messages in thread
* Re: [PATCH 2/2] Implement a simple delta_base cache
2007-03-17 21:45 ` Linus Torvalds
@ 2007-03-17 22:37 ` Junio C Hamano
2007-03-17 23:09 ` Linus Torvalds
2007-03-18 1:13 ` Nicolas Pitre
2007-03-17 23:12 ` Junio C Hamano
2007-03-18 1:14 ` Morten Welinder
2 siblings, 2 replies; 79+ messages in thread
From: Junio C Hamano @ 2007-03-17 22:37 UTC (permalink / raw)
To: Linus Torvalds; +Cc: Nicolas Pitre, Git Mailing List
Linus Torvalds <torvalds@linux-foundation.org> writes:
> ie, we still re-generate some of the objects multiple times, but now,
> rather than generating them (on average) 20+ times each, we now generate
> them an average of just 1.3 times each. Which explains why the wall-time
> goes down by over a factor of two.
This is beautiful. You only cache what we were about to discard
anyway, and when giving a cached one out, you invalidate the
cached entry, so there is no way the patch can introduce leaks
nor double-frees and it is absolutely safe (as long as we can
pin the packed_git structure, which I think is the case --- even
when we re-read the packs, I do not think we discard old ones).
I've thought about possible ways to improve on it, but came up
almost empty.
When unpacking a depth-3 deltified object A, the code finds the
target object A (which is a delta), ask for its base B and put B
in the cache after using it to reconstitute A. While doing so,
the first-generation base B is also a delta so its base C (which
is a non-delta) is found and placed in the cache. When A is
returned, the cache has B and C. If you ask for B at this
point, we read the delta, pick up its base C from the cache,
apply, and return while putting C back in the cache. If you ask
for A after that, we do not read from the cache, although it is
available.
Which feels a bit wasteful at first sight, and we *could* make
read_packed_sha1() also steal from the cache, but after thinking
about it a bit, I am not sure if it is worth it. The contract
between read_packed_sha1() and read_sha1_file() and its callers
is that the returned data belongs to the caller and it is a
responsibility for the caller to free the buffer, and also the
caller is free to modify it, so stealing from the cache from
that codepath means an extra allocation and memcpy. If the
object stolen from the cache is of sufficient depth, it might be
worth it, but to decide it we somehow need to compute and store
which delta depth the cached one is at.
In any way, your code makes a deeply delitified packfiles a lot
more practical. As long as the working set of delta chains fits
in the cache, after unpacking the longuest delta, the objects on
the chain can be had by one lookup and one delta application.
Very good job.
> In general, this all seems very cool. The patches are simple enough that I
> think this is very safe to merge indeed: the only question I have is that
> somebody should verify that the "struct packed_git *p" is stable over the
> whole lifetime of a process - so that we can use it as a hash key without
> having to invalidate hashes if we unmap a pack (I *think* we just unmap
> the virtual mapping, and "struct packed_git *" stays valid, but Junio
> should ack that for me).
Ack ;-)
^ permalink raw reply [flat|nested] 79+ messages in thread
* Re: [PATCH 2/2] Implement a simple delta_base cache
2007-03-17 19:44 ` [PATCH 2/2] Implement a simple delta_base cache Linus Torvalds
2007-03-17 21:45 ` Linus Torvalds
@ 2007-03-17 22:44 ` Linus Torvalds
1 sibling, 0 replies; 79+ messages in thread
From: Linus Torvalds @ 2007-03-17 22:44 UTC (permalink / raw)
To: Junio C Hamano, Nicolas Pitre; +Cc: Git Mailing List
On Sat, 17 Mar 2007, Linus Torvalds wrote:
>
> This trivial 256-entry delta_base cache improves performance for some
> loads by a factor of 2.5 or so.
Btw, final comment on this issue:
I was initially a bit worried about optimizing for just the "git log" with
pathspec or "git blame" kind of behaviour, and possibly pessimizing some
other load.
But the way the caching works, this is likely to be faster (or at least
not slower) even for something that doesn't ever need the cache (which in
turn is likely to be because it's a smaller footprint query and only works
on one version).
Because the way the cache works, it doesn't really do any extra work: it
basically just delays the "free()" on the buffer we allocated. So for
really small footprints it just avoids the overhead of free() (let the OS
reap the pages for it at exit), and for bigger footprints (that end up
replacing the cache entries) it will just do the same work a bit later.
Because it's a simple direct-mapped cache, the only cost is the (trivial)
hash of a few instructions, and possibly the slightly bigger D$ footprint.
I would strongly suspect that even on loads where it doesn't help by
reusing the cached objects, the delayed free'ing on its own is as likely
to help as it is to hurt.
So there really shouldn't be any downsides.
Testing on some other loads (for example, drivers/scsi/ has more activity
than drivers/usb/), the 2x performance win seems to happen for other
things too. For drivers/scsi, the log generating went down from 3.582s
(best) to 1.448s.
"git blame Makefile" went from 1.802s to 1.243s (both best-case numbers
again: a smaller win, but still a win), but there the issue seems to be
that with a file like that, we actually spend most of our time comparing
different versions.
For the "git blame Makefile" case *all* of zlib combined is just 18%,
while the ostensibly trivial "cmp_suspect()" is 23% and another 11% is
from "assign_blame()" - so for top-level entries the costs would seem to
tend to be in the blame algorithm itself, rather than in the actual object
handling.
(I'm sure that could be improved too, but the take-home message from this
is that zlib wasn't really the problem, and our stupid re-generation of
the same delta base was.
Linus
^ permalink raw reply [flat|nested] 79+ messages in thread
* Re: [PATCH 2/2] Implement a simple delta_base cache
2007-03-17 22:37 ` Junio C Hamano
@ 2007-03-17 23:09 ` Linus Torvalds
2007-03-17 23:54 ` Linus Torvalds
2007-03-18 1:13 ` Nicolas Pitre
1 sibling, 1 reply; 79+ messages in thread
From: Linus Torvalds @ 2007-03-17 23:09 UTC (permalink / raw)
To: Junio C Hamano; +Cc: Nicolas Pitre, Git Mailing List
On Sat, 17 Mar 2007, Junio C Hamano wrote:
>
> When unpacking a depth-3 deltified object A, the code finds the
> target object A (which is a delta), ask for its base B and put B
> in the cache after using it to reconstitute A. While doing so,
> the first-generation base B is also a delta so its base C (which
> is a non-delta) is found and placed in the cache. When A is
> returned, the cache has B and C. If you ask for B at this
> point, we read the delta, pick up its base C from the cache,
> apply, and return while putting C back in the cache. If you ask
> for A after that, we do not read from the cache, although it is
> available.
Yes.
I debated that a bit with myself, but decided that:
(a) it probably doesn't really matter a lot (but I don't have the
numbers)
(b) trying to *also* fill non-delta-base queries from the delta-base
cache actually complicates things a lot. Surprisingly much so (the
current logic of removing the entry from the cache only to re-insert
it after being used made the memory management totally trivial, as
you noticed)
(c) and regardless, we could decide to do a more extensive caching layer
later if we really wanted to, and at that point it probably makes
more sense to integrate it with the delta-base cache.
Most git objects are use-once, which is why we really *just* save the
flag bits and the SHA1 hash name itself in "struct object", but doing
a generic caching layer for object content would likely obviate the
need for the current logic to do "save_commit_buffer".
That (c) in particular was what made me think that it's better to keep it
simple and obvious for now, since even the simple thing largely fixes the
performance issue. Almost three seconds I felt bad about, while just over
a second for something as complex as "git log drivers/usb/" I just cannot
make myself worry about.
> In any way, your code makes a deeply delitified packfiles a lot
> more practical. As long as the working set of delta chains fits
> in the cache, after unpacking the longuest delta, the objects on
> the chain can be had by one lookup and one delta application.
Yeah. I think it would be good to probably (separately and as "further
tweaks"):
- have somebody actually look at hit-rates for different repositories and
hash sizes.
- possibly allow people to set the hash size as a config option, if it
turns out that certain repository layouts or usage scenarios end up
preferring bigger caches.
For example, it may be that for historical archives you might want to
have deeper delta queues to make the repository smaller, and if they
are big anyway maybe they would prefer to have a larger-than-normal
cache as a result. On the other hand, if you are memory-constrained,
maybe you'd prefer to re-generate the objects and waste a bit of CPU
rather than cache the results.
But neither of the above is really an argument against the patch, just a
"there's certainly room for more work here if anybody cares".
> Very good job.
I'm pretty happy with the results myself. Partly because the patches just
ended up looking so *nice*.
Linus
^ permalink raw reply [flat|nested] 79+ messages in thread
* Re: [PATCH 2/2] Implement a simple delta_base cache
2007-03-17 21:45 ` Linus Torvalds
2007-03-17 22:37 ` Junio C Hamano
@ 2007-03-17 23:12 ` Junio C Hamano
2007-03-17 23:24 ` Linus Torvalds
2007-03-18 1:14 ` Morten Welinder
2 siblings, 1 reply; 79+ messages in thread
From: Junio C Hamano @ 2007-03-17 23:12 UTC (permalink / raw)
To: Linus Torvalds; +Cc: Nicolas Pitre, Git Mailing List
Linus Torvalds <torvalds@linux-foundation.org> writes:
> Here's the trivial patch to extend the caching to 1k entries if somebody
> cares. I don't know if the small added performance is worth it.
This largely would depend on the project, but if a blob that is
cached is 20kB each, a 1024-entry cache would grow to 20MB. We
may need to introduce early eviction of cached objects with
total cache size limit, configurable per repository.
^ permalink raw reply [flat|nested] 79+ messages in thread
* Re: [PATCH 2/2] Implement a simple delta_base cache
2007-03-17 23:12 ` Junio C Hamano
@ 2007-03-17 23:24 ` Linus Torvalds
2007-03-17 23:52 ` Jon Smirl
0 siblings, 1 reply; 79+ messages in thread
From: Linus Torvalds @ 2007-03-17 23:24 UTC (permalink / raw)
To: Junio C Hamano; +Cc: Nicolas Pitre, Git Mailing List
On Sat, 17 Mar 2007, Junio C Hamano wrote:
>
> This largely would depend on the project, but if a blob that is
> cached is 20kB each, a 1024-entry cache would grow to 20MB. We
> may need to introduce early eviction of cached objects with
> total cache size limit, configurable per repository.
One thing that I considered was to limit the delta-base cache to just tree
entries. Those tend to be the really performance-sensitive ones - by the
time you actually unpack blob entries, you're going to do something with
that *single* entry anyway (like compare it to another blob), and the cost
of unpacking the entry is likely to not be really all that noticeable.
That said, it was just simpler to do it unconditionally, and it obviously
*works* fine regardless of the object type, so limiting it to trees is a
bit sad. And since the intensive tree operations tend to be in a separate
phase (ie the commit simplification phase) from the the blob operations
(say, doing "git log -p <pathspec>"), I suspect that the cache locality
would still remain good.
So I didn't do anything along the lines of "only cache for case Xyzzy".
But yes, especially if a project has big blobs, it might make sense to
limit by full size of the cached entries some way.
Linus
^ permalink raw reply [flat|nested] 79+ messages in thread
* Re: [PATCH 2/2] Implement a simple delta_base cache
2007-03-17 23:24 ` Linus Torvalds
@ 2007-03-17 23:52 ` Jon Smirl
0 siblings, 0 replies; 79+ messages in thread
From: Jon Smirl @ 2007-03-17 23:52 UTC (permalink / raw)
To: Linus Torvalds; +Cc: Junio C Hamano, Nicolas Pitre, Git Mailing List
If you still have a Mozilla pack file around it would be a good test
case. It has delta chains thousands of entries long. If I remember
correctly one had over 4,000 deltas.
--
Jon Smirl
jonsmirl@gmail.com
^ permalink raw reply [flat|nested] 79+ messages in thread
* Re: [PATCH 2/2] Implement a simple delta_base cache
2007-03-17 23:09 ` Linus Torvalds
@ 2007-03-17 23:54 ` Linus Torvalds
0 siblings, 0 replies; 79+ messages in thread
From: Linus Torvalds @ 2007-03-17 23:54 UTC (permalink / raw)
To: Junio C Hamano; +Cc: Nicolas Pitre, Git Mailing List
On Sat, 17 Mar 2007, Linus Torvalds wrote:
>
> (a) it probably doesn't really matter a lot (but I don't have the
> numbers)
Well, to some degree I obviously *do* have the numbers.
I have the numbers that we used to re-generate the object data over five
*hundred* times per object for some cases, and that I got the average
such delta-base usage down from 20x to 1.1-1.3x depending on cache size.
In contrast, the "use delta-base also for non-delta queries" fairly
obviously cannot touch those kinds of numbers. We migth avoid a *few*
object generation cases, but we're not looking at factors of 20 for any
kind of sane cases.
So I do think that a higher-level caching approach can work too, but it's
going to be more effective in other areas:
- get rid of some ugly hacks (like the "save_commit_buffer" thing I
mentioned)
- possibly help some insane loads (eg cases where we really *do* end up
seeing the same object over and over again, perhaps simply because some
idiotic automated commit system ends up switching between a few states
back-and-forth).
I really think the "insane loads" thing is unlikely, but I could construct
some crazy usage scenario where a cache of objects in general (and not
just delta bases) would work. I don't think it's a very realistic case,
but who knows - people sometimes do really stupid things.
Linus
^ permalink raw reply [flat|nested] 79+ messages in thread
* Re: [PATCH 2/2] Implement a simple delta_base cache
2007-03-17 22:37 ` Junio C Hamano
2007-03-17 23:09 ` Linus Torvalds
@ 2007-03-18 1:13 ` Nicolas Pitre
2007-03-18 7:47 ` Junio C Hamano
1 sibling, 1 reply; 79+ messages in thread
From: Nicolas Pitre @ 2007-03-18 1:13 UTC (permalink / raw)
To: Junio C Hamano; +Cc: Linus Torvalds, Git Mailing List
On Sat, 17 Mar 2007, Junio C Hamano wrote:
> When unpacking a depth-3 deltified object A, the code finds the
> target object A (which is a delta), ask for its base B and put B
> in the cache after using it to reconstitute A. While doing so,
> the first-generation base B is also a delta so its base C (which
> is a non-delta) is found and placed in the cache. When A is
> returned, the cache has B and C. If you ask for B at this
> point, we read the delta, pick up its base C from the cache,
> apply, and return while putting C back in the cache. If you ask
> for A after that, we do not read from the cache, although it is
> available.
>
> Which feels a bit wasteful at first sight, and we *could* make
> read_packed_sha1() also steal from the cache, but after thinking
> about it a bit, I am not sure if it is worth it. The contract
> between read_packed_sha1() and read_sha1_file() and its callers
> is that the returned data belongs to the caller and it is a
> responsibility for the caller to free the buffer, and also the
> caller is free to modify it, so stealing from the cache from
> that codepath means an extra allocation and memcpy.
So?
A malloc() + memcpy() will always be faster than mmap() + malloc() +
inflate(). If the data is already there it is certainly better to copy
it straight away.
With the patch below I can do 'git log drivers/scsi/ > /dev/null' about
7% faster. I bet it might be even more on those platforms with bad
mmap() support.
Signed-off-by: Nicolas Pitre <nico@cam.org>
---
diff --git a/sha1_file.c b/sha1_file.c
index a7e3a2a..ee64865 100644
--- a/sha1_file.c
+++ b/sha1_file.c
@@ -1372,7 +1372,7 @@ static unsigned long pack_entry_hash(struct packed_git *p, off_t base_offset)
}
static void *cache_or_unpack_entry(struct packed_git *p, off_t base_offset,
- unsigned long *base_size, enum object_type *type)
+ unsigned long *base_size, enum object_type *type, int keep_cache)
{
void *ret;
unsigned long hash = pack_entry_hash(p, base_offset);
@@ -1384,7 +1384,13 @@ static void *cache_or_unpack_entry(struct packed_git *p, off_t base_offset,
return unpack_entry(p, base_offset, type, base_size);
found_cache_entry:
- ent->data = NULL;
+ if (!keep_cache)
+ ent->data = NULL;
+ else {
+ ret = xmalloc(ent->size + 1);
+ memcpy(ret, ent->data, ent->size);
+ ((char *)ret)[ent->size] = 0;
+ }
*type = ent->type;
*base_size = ent->size;
return ret;
@@ -1418,7 +1424,7 @@ static void *unpack_delta_entry(struct packed_git *p,
off_t base_offset;
base_offset = get_delta_base(p, w_curs, &curpos, *type, obj_offset);
- base = cache_or_unpack_entry(p, base_offset, &base_size, type);
+ base = cache_or_unpack_entry(p, base_offset, &base_size, type, 0);
if (!base)
die("failed to read delta base object"
" at %"PRIuMAX" from %s",
@@ -1615,7 +1621,7 @@ static void *read_packed_sha1(const unsigned char *sha1,
if (!find_pack_entry(sha1, &e, NULL))
return NULL;
else
- return unpack_entry(e.p, e.offset, type, size);
+ return cache_or_unpack_entry(e.p, e.offset, size, type, 1);
}
/*
^ permalink raw reply related [flat|nested] 79+ messages in thread
* Re: [PATCH 2/2] Implement a simple delta_base cache
2007-03-17 21:45 ` Linus Torvalds
2007-03-17 22:37 ` Junio C Hamano
2007-03-17 23:12 ` Junio C Hamano
@ 2007-03-18 1:14 ` Morten Welinder
2007-03-18 1:29 ` Linus Torvalds
2007-03-18 6:28 ` Avi Kivity
2 siblings, 2 replies; 79+ messages in thread
From: Morten Welinder @ 2007-03-18 1:14 UTC (permalink / raw)
To: Linus Torvalds; +Cc: Junio C Hamano, Nicolas Pitre, Git Mailing List
> samples % app name symbol name
> 41527 15.6550 git strlen
Almost 16% in strlen? Ugh!
That's a lot of strings, or perhaps very long strings. Or a profiling bug.
M.
^ permalink raw reply [flat|nested] 79+ messages in thread
* Re: [PATCH 2/2] Implement a simple delta_base cache
2007-03-18 1:14 ` Morten Welinder
@ 2007-03-18 1:29 ` Linus Torvalds
2007-03-18 1:38 ` Nicolas Pitre
2007-03-18 1:44 ` [PATCH 2/2] Implement a simple delta_base cache Linus Torvalds
2007-03-18 6:28 ` Avi Kivity
1 sibling, 2 replies; 79+ messages in thread
From: Linus Torvalds @ 2007-03-18 1:29 UTC (permalink / raw)
To: Morten Welinder; +Cc: Junio C Hamano, Nicolas Pitre, Git Mailing List
On Sat, 17 Mar 2007, Morten Welinder wrote:
>
> > samples % app name symbol name
> > 41527 15.6550 git strlen
>
> Almost 16% in strlen? Ugh!
>
> That's a lot of strings, or perhaps very long strings. Or a profiling bug.
It's likely real, and the problem is likely lots of small strings.
Each git tree entry is:
"<octal mode> name\0" <20-byte sha1>
so you do have a *lot* of strlen() calls when doing any tree parsing. And
for some inexplicable reason, glibc thinks strings are long on average, so
it has a fancy algorithm to do 8 bytes at a time and tries to do things
aligned etc.
The size of strlen() on x86-64 with glibc is 232 bytes. I'm not kidding.
Linus
^ permalink raw reply [flat|nested] 79+ messages in thread
* Re: [PATCH 2/2] Implement a simple delta_base cache
2007-03-18 1:29 ` Linus Torvalds
@ 2007-03-18 1:38 ` Nicolas Pitre
2007-03-18 1:55 ` Linus Torvalds
2007-03-18 1:44 ` [PATCH 2/2] Implement a simple delta_base cache Linus Torvalds
1 sibling, 1 reply; 79+ messages in thread
From: Nicolas Pitre @ 2007-03-18 1:38 UTC (permalink / raw)
To: Linus Torvalds; +Cc: Morten Welinder, Junio C Hamano, Git Mailing List
On Sat, 17 Mar 2007, Linus Torvalds wrote:
>
>
> On Sat, 17 Mar 2007, Morten Welinder wrote:
> >
> > > samples % app name symbol name
> > > 41527 15.6550 git strlen
> >
> > Almost 16% in strlen? Ugh!
> >
> > That's a lot of strings, or perhaps very long strings. Or a profiling bug.
>
> It's likely real, and the problem is likely lots of small strings.
>
> Each git tree entry is:
>
> "<octal mode> name\0" <20-byte sha1>
>
> so you do have a *lot* of strlen() calls when doing any tree parsing.
This is definitely an area where pack v4 will bring that cost down to
zero.
Nicolas
^ permalink raw reply [flat|nested] 79+ messages in thread
* Re: [PATCH 2/2] Implement a simple delta_base cache
2007-03-18 1:29 ` Linus Torvalds
2007-03-18 1:38 ` Nicolas Pitre
@ 2007-03-18 1:44 ` Linus Torvalds
1 sibling, 0 replies; 79+ messages in thread
From: Linus Torvalds @ 2007-03-18 1:44 UTC (permalink / raw)
To: Morten Welinder; +Cc: Junio C Hamano, Nicolas Pitre, Git Mailing List
On Sat, 17 Mar 2007, Linus Torvalds wrote:
> >
> > That's a lot of strings, or perhaps very long strings. Or a profiling bug.
Btw, the reason I'm pretty sure that it's not a profiling bug is that
(a) the rest of the profile looks fine
(b) it actually matches the rest of the profile.
In particular, while you reacted to
samples % app name symbol name
41527 15.6550 git strlen
you didn't bat an eye on
9240 3.4833 git get_mode
8863 3.3412 git tree_entry_extract
ie over 3% of time spent in tree entry extract and get_mode. But take
another look at that tree_entry_extract() function in particular and look
what it does, and ask yourself: if *that* function takes up 3% of time,
what does it tell you about strlen()?
(Side note: we could probably improve "strlen()" in particular. We
sometimes call it twice: look at "entry_extract()", which calls strlen()
on the tree entry extract, but then *also* calls strlen on the resulting
path.
I suspect the
a->pathlen = strlen(a->path);
could be written as
a->pathlen = (char *)a->sha1 - (char *)a->path - 1;
but somebody should check that I didn't off-by-one or something. Also, it
migt be better to make that part of "tree_entry_extract()" itself, because
other callers do the same thing (see "find_tree_entry()": doing a
"strlen()" on the path return of tree_entry_extract() seems to be a common
pattern).
HOWEVER!
Once we get to *that* level of optimizations, we're doing pretty damn
well. I'm sure we could probably cut down that strlen() from 16% to 8% by
being smart about it, but still - this is a "good kind of problem" to
have, if these things are your lowest-hanging fruit!
Maybe it all boils down to the same thing: I just can't seem to be really
upset about "git log drivers/usb/ > /dev/null" taking all of a second. It
just doesn't strike me as a performance problem ;)
Linus
^ permalink raw reply [flat|nested] 79+ messages in thread
* Re: [PATCH 2/2] Implement a simple delta_base cache
2007-03-18 1:38 ` Nicolas Pitre
@ 2007-03-18 1:55 ` Linus Torvalds
2007-03-18 2:03 ` Nicolas Pitre
0 siblings, 1 reply; 79+ messages in thread
From: Linus Torvalds @ 2007-03-18 1:55 UTC (permalink / raw)
To: Nicolas Pitre; +Cc: Morten Welinder, Junio C Hamano, Git Mailing List
On Sat, 17 Mar 2007, Nicolas Pitre wrote:
>
> This is definitely an area where pack v4 will bring that cost down to
> zero.
Heh. I believe that when I see it. The thing is, unless you re-generate
the tree object data structures, you'll have to have totally different
tree walkers for different tree types, and it will all be quite ugly and
complex. And "ugly and complex" seldom translates into "zero cost".
Linus
^ permalink raw reply [flat|nested] 79+ messages in thread
* Re: [PATCH 2/2] Implement a simple delta_base cache
2007-03-18 1:55 ` Linus Torvalds
@ 2007-03-18 2:03 ` Nicolas Pitre
2007-03-18 2:20 ` Linus Torvalds
0 siblings, 1 reply; 79+ messages in thread
From: Nicolas Pitre @ 2007-03-18 2:03 UTC (permalink / raw)
To: Linus Torvalds; +Cc: Morten Welinder, Junio C Hamano, Git Mailing List
On Sat, 17 Mar 2007, Linus Torvalds wrote:
>
>
> On Sat, 17 Mar 2007, Nicolas Pitre wrote:
> >
> > This is definitely an area where pack v4 will bring that cost down to
> > zero.
>
> Heh. I believe that when I see it. The thing is, unless you re-generate
> the tree object data structures, you'll have to have totally different
> tree walkers for different tree types, and it will all be quite ugly and
> complex. And "ugly and complex" seldom translates into "zero cost".
Well... in my opinion it is the _current_ tree walker that is quite ugly
and complex. It is always messier to parse strings than fixed width
binary fields.
Nicolas
^ permalink raw reply [flat|nested] 79+ messages in thread
* Re: [PATCH 2/2] Implement a simple delta_base cache
2007-03-18 2:03 ` Nicolas Pitre
@ 2007-03-18 2:20 ` Linus Torvalds
2007-03-18 3:00 ` Nicolas Pitre
2007-03-18 3:06 ` [PATCH 3/2] Avoid unnecessary strlen() calls Linus Torvalds
0 siblings, 2 replies; 79+ messages in thread
From: Linus Torvalds @ 2007-03-18 2:20 UTC (permalink / raw)
To: Nicolas Pitre; +Cc: Morten Welinder, Junio C Hamano, Git Mailing List
On Sat, 17 Mar 2007, Nicolas Pitre wrote:
>
> Well... in my opinion it is the _current_ tree walker that is quite ugly
> and complex. It is always messier to parse strings than fixed width
> binary fields.
Sure. On the other hand, text is what made things easy to do initially,
and you're missing one *BIG* clue: you cannot remote the support without
losing compatibility with all traditional object formats.
So you have no choice. You need to support the text representation. As a
result, *your* code will now be way more ugly and messy.
The thing is, parsing some little text may sound expensive, but if the
expense is in finding the end of the string, we're doing really well.
In other words: the data structures are both simple and straightforward,
and the only reason strlen() shows up at all is:
- we pass strings around as just C strings, even when we know their
lengths. Prime example: look at tree-diff.c. And when you look at it,
realize that *for*every*single*strlen* in that file except for the very
last one (which is only used once per process for setup) we actually
know the string length from before, but we (well, *I*) decided that it
wasn't worth passing down as a parameter all the time.
- the simple parsing of the tree itself (which really isn't that
expensive - the real expense is bringing the data into the CPU cache,
but that's something we'd need to do *anyway*).
So I seriously suspect that you could get the strlen() overhead down from
that 16% pretty easily, but you'd have to pass the length of the "base"
string along all the time (and in the tree_entry cases you'd replace the
"strlen()" calls with a call to something like
static inline int tree_entry_len(const char *name, const unsigned char *sha1)
{
return (char *)sha1 - (char *)name - 1;
}
which will do it for you).
But what you're ignoring here is that "16%" may sound like a huge deal,
but it's 16% of somethng that takes 1 second, and that other SCM's cannot
do AT ALL.
Linus
^ permalink raw reply [flat|nested] 79+ messages in thread
* Re: [PATCH 2/2] Implement a simple delta_base cache
2007-03-18 2:20 ` Linus Torvalds
@ 2007-03-18 3:00 ` Nicolas Pitre
2007-03-18 3:31 ` Linus Torvalds
2007-03-18 3:06 ` [PATCH 3/2] Avoid unnecessary strlen() calls Linus Torvalds
1 sibling, 1 reply; 79+ messages in thread
From: Nicolas Pitre @ 2007-03-18 3:00 UTC (permalink / raw)
To: Linus Torvalds; +Cc: Morten Welinder, Junio C Hamano, Git Mailing List
On Sat, 17 Mar 2007, Linus Torvalds wrote:
>
>
> On Sat, 17 Mar 2007, Nicolas Pitre wrote:
> >
> > Well... in my opinion it is the _current_ tree walker that is quite ugly
> > and complex. It is always messier to parse strings than fixed width
> > binary fields.
>
> Sure. On the other hand, text is what made things easy to do initially,
Oh indeed. No argument there.
> and you're missing one *BIG* clue: you cannot remote the support without
> losing compatibility with all traditional object formats.
>
> So you have no choice. You need to support the text representation. As a
> result, *your* code will now be way more ugly and messy.
Depends. We currently have separate parsers for trees, commits, tags,
etc. That should be easy enough to add another (separate) parser for
new tree objects while still having a common higher level accessor
interface like tree_entry().
But right now we only regenerate the text representation whenever the
binary representation is encountered just to make things easy to do, and
yet we still have a performance gain already in _addition_ to a net
saving in disk footprint.
> The thing is, parsing some little text may sound expensive, but if the
> expense is in finding the end of the string, we're doing really well.
Of course the current tree parser will remain, probably forever. And it
is always a good thing to optimize it further when ever possible.
> But what you're ignoring here is that "16%" may sound like a huge deal,
> but it's 16% of somethng that takes 1 second, and that other SCM's cannot
> do AT ALL.
Sure. But at this point the reference to compare GIT performance
against might be GIT itself. And while 1 second is really nice in this
case, there are some repos where it could be (and has already been
reported to be) much more.
I still have a feeling that we can do even better than we do now. Much
much better than 16% actually. But that require a new data format that
is designed for speed.
We'll see.
Nicolas
^ permalink raw reply [flat|nested] 79+ messages in thread
* [PATCH 3/2] Avoid unnecessary strlen() calls
2007-03-18 2:20 ` Linus Torvalds
2007-03-18 3:00 ` Nicolas Pitre
@ 2007-03-18 3:06 ` Linus Torvalds
2007-03-18 9:45 ` Junio C Hamano
1 sibling, 1 reply; 79+ messages in thread
From: Linus Torvalds @ 2007-03-18 3:06 UTC (permalink / raw)
To: Nicolas Pitre, Junio C Hamano; +Cc: Morten Welinder, Git Mailing List
This is a micro-optimization that grew out of the mailing list discussion
about "strlen()" showing up in profiles.
We used to pass regular C strings around to the low-level tree walking
routines, and while this worked fine, it meant that we needed to call
strlen() on strings that the caller always actually knew the size of
anyway.
So pass the length of the string down wih the string, and avoid
unnecessary calls to strlen(). Also, when extracting a pathname from a
tree entry, use "tree_entry_len()" instead of strlen(), since the length
of the pathname is directly calculable from the decoded tree entry itself
without having to actually do another strlen().
This shaves off another ~5-10% from some loads that are very tree
intensive (notably doing commit filtering by a pathspec).
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>"
---
On Sat, 17 Mar 2007, Linus Torvalds wrote:
>
> - we pass strings around as just C strings, even when we know their
> lengths. Prime example: look at tree-diff.c. And when you look at it,
> realize that *for*every*single*strlen* in that file except for the very
> last one (which is only used once per process for setup) we actually
> know the string length from before, but we (well, *I*) decided that it
> wasn't worth passing down as a parameter all the time.
So here's the patch.
It definitely cuts down on CPU usage, and I actually left one extra
"strlen()" around, simply because I didn't want to mess with the exported
interface of "diff_tree()".
But that other strlen() is also one that is done *once* for the whole
tree, so from a performance standpoint it doesn't matter (we *could* have
passed in that length too, but that would have involved more changes that
simply aren't really useful).
Does it help? Yes it does. It takes another 5-10% off my test-case.
"strlen()" still exists, but it's basically half of what it used to be
because we now basically only call it when literally parsing the tree data
itself (ie now it's ~8% of the total, and no longer the hottest entry.
Is it worth it? If it was just a random micro-optimization I might not
care, but I guess it's not that ugly to pass an extra "baselen" around all
the time. And that "tree_entry_len()" helper function is actually quite
nice. So yeah, I'd suggest applying this one just because it's actually a
perfectly fine patch and it does speed things up.
So it *is* very much a micro-optimization, but one that doesn't really
make the code any uglier, so why not..
I still think that if we do these kinds of optimizations and they matter,
that shows just how *well* we're actually doing here!
Anyway, Junio, it passes all the tests, as well as passing my "looks
obviously correct" filter, so..
Linus
---
diff --git a/tree-diff.c b/tree-diff.c
index c827582..f89b9d3 100644
--- a/tree-diff.c
+++ b/tree-diff.c
@@ -5,9 +5,8 @@
#include "diff.h"
#include "tree.h"
-static char *malloc_base(const char *base, const char *path, int pathlen)
+static char *malloc_base(const char *base, int baselen, const char *path, int pathlen)
{
- int baselen = strlen(base);
char *newbase = xmalloc(baselen + pathlen + 2);
memcpy(newbase, base, baselen);
memcpy(newbase + baselen, path, pathlen);
@@ -16,9 +15,9 @@ static char *malloc_base(const char *base, const char *path, int pathlen)
}
static void show_entry(struct diff_options *opt, const char *prefix, struct tree_desc *desc,
- const char *base);
+ const char *base, int baselen);
-static int compare_tree_entry(struct tree_desc *t1, struct tree_desc *t2, const char *base, struct diff_options *opt)
+static int compare_tree_entry(struct tree_desc *t1, struct tree_desc *t2, const char *base, int baselen, struct diff_options *opt)
{
unsigned mode1, mode2;
const char *path1, *path2;
@@ -28,15 +27,15 @@ static int compare_tree_entry(struct tree_desc *t1, struct tree_desc *t2, const
sha1 = tree_entry_extract(t1, &path1, &mode1);
sha2 = tree_entry_extract(t2, &path2, &mode2);
- pathlen1 = strlen(path1);
- pathlen2 = strlen(path2);
+ pathlen1 = tree_entry_len(path1, sha1);
+ pathlen2 = tree_entry_len(path2, sha2);
cmp = base_name_compare(path1, pathlen1, mode1, path2, pathlen2, mode2);
if (cmp < 0) {
- show_entry(opt, "-", t1, base);
+ show_entry(opt, "-", t1, base, baselen);
return -1;
}
if (cmp > 0) {
- show_entry(opt, "+", t2, base);
+ show_entry(opt, "+", t2, base, baselen);
return 1;
}
if (!opt->find_copies_harder && !hashcmp(sha1, sha2) && mode1 == mode2)
@@ -47,14 +46,14 @@ static int compare_tree_entry(struct tree_desc *t1, struct tree_desc *t2, const
* file, we need to consider it a remove and an add.
*/
if (S_ISDIR(mode1) != S_ISDIR(mode2)) {
- show_entry(opt, "-", t1, base);
- show_entry(opt, "+", t2, base);
+ show_entry(opt, "-", t1, base, baselen);
+ show_entry(opt, "+", t2, base, baselen);
return 0;
}
if (opt->recursive && S_ISDIR(mode1)) {
int retval;
- char *newbase = malloc_base(base, path1, pathlen1);
+ char *newbase = malloc_base(base, baselen, path1, pathlen1);
if (opt->tree_in_recursive)
opt->change(opt, mode1, mode2,
sha1, sha2, base, path1);
@@ -67,20 +66,20 @@ static int compare_tree_entry(struct tree_desc *t1, struct tree_desc *t2, const
return 0;
}
-static int interesting(struct tree_desc *desc, const char *base, struct diff_options *opt)
+static int interesting(struct tree_desc *desc, const char *base, int baselen, struct diff_options *opt)
{
const char *path;
+ const unsigned char *sha1;
unsigned mode;
int i;
- int baselen, pathlen;
+ int pathlen;
if (!opt->nr_paths)
return 1;
- (void)tree_entry_extract(desc, &path, &mode);
+ sha1 = tree_entry_extract(desc, &path, &mode);
- pathlen = strlen(path);
- baselen = strlen(base);
+ pathlen = tree_entry_len(path, sha1);
for (i=0; i < opt->nr_paths; i++) {
const char *match = opt->paths[i];
@@ -121,18 +120,18 @@ static int interesting(struct tree_desc *desc, const char *base, struct diff_opt
}
/* A whole sub-tree went away or appeared */
-static void show_tree(struct diff_options *opt, const char *prefix, struct tree_desc *desc, const char *base)
+static void show_tree(struct diff_options *opt, const char *prefix, struct tree_desc *desc, const char *base, int baselen)
{
while (desc->size) {
- if (interesting(desc, base, opt))
- show_entry(opt, prefix, desc, base);
+ if (interesting(desc, base, baselen, opt))
+ show_entry(opt, prefix, desc, base, baselen);
update_tree_entry(desc);
}
}
/* A file entry went away or appeared */
static void show_entry(struct diff_options *opt, const char *prefix, struct tree_desc *desc,
- const char *base)
+ const char *base, int baselen)
{
unsigned mode;
const char *path;
@@ -140,7 +139,8 @@ static void show_entry(struct diff_options *opt, const char *prefix, struct tree
if (opt->recursive && S_ISDIR(mode)) {
enum object_type type;
- char *newbase = malloc_base(base, path, strlen(path));
+ int pathlen = tree_entry_len(path, sha1);
+ char *newbase = malloc_base(base, baselen, path, pathlen);
struct tree_desc inner;
void *tree;
@@ -149,7 +149,7 @@ static void show_entry(struct diff_options *opt, const char *prefix, struct tree
die("corrupt tree sha %s", sha1_to_hex(sha1));
inner.buf = tree;
- show_tree(opt, prefix, &inner, newbase);
+ show_tree(opt, prefix, &inner, newbase, baselen + 1 + pathlen);
free(tree);
free(newbase);
@@ -160,26 +160,28 @@ static void show_entry(struct diff_options *opt, const char *prefix, struct tree
int diff_tree(struct tree_desc *t1, struct tree_desc *t2, const char *base, struct diff_options *opt)
{
+ int baselen = strlen(base);
+
while (t1->size | t2->size) {
- if (opt->nr_paths && t1->size && !interesting(t1, base, opt)) {
+ if (opt->nr_paths && t1->size && !interesting(t1, base, baselen, opt)) {
update_tree_entry(t1);
continue;
}
- if (opt->nr_paths && t2->size && !interesting(t2, base, opt)) {
+ if (opt->nr_paths && t2->size && !interesting(t2, base, baselen, opt)) {
update_tree_entry(t2);
continue;
}
if (!t1->size) {
- show_entry(opt, "+", t2, base);
+ show_entry(opt, "+", t2, base, baselen);
update_tree_entry(t2);
continue;
}
if (!t2->size) {
- show_entry(opt, "-", t1, base);
+ show_entry(opt, "-", t1, base, baselen);
update_tree_entry(t1);
continue;
}
- switch (compare_tree_entry(t1, t2, base, opt)) {
+ switch (compare_tree_entry(t1, t2, base, baselen, opt)) {
case -1:
update_tree_entry(t1);
continue;
diff --git a/tree-walk.c b/tree-walk.c
index 70f8999..a4a4e2a 100644
--- a/tree-walk.c
+++ b/tree-walk.c
@@ -32,7 +32,7 @@ static void entry_clear(struct name_entry *a)
static void entry_extract(struct tree_desc *t, struct name_entry *a)
{
a->sha1 = tree_entry_extract(t, &a->path, &a->mode);
- a->pathlen = strlen(a->path);
+ a->pathlen = tree_entry_len(a->path, a->sha1);
}
void update_tree_entry(struct tree_desc *desc)
@@ -169,7 +169,7 @@ static int find_tree_entry(struct tree_desc *t, const char *name, unsigned char
sha1 = tree_entry_extract(t, &entry, mode);
update_tree_entry(t);
- entrylen = strlen(entry);
+ entrylen = tree_entry_len(entry, sha1);
if (entrylen > namelen)
continue;
cmp = memcmp(name, entry, entrylen);
diff --git a/tree-walk.h b/tree-walk.h
index e57befa..a0d7afd 100644
--- a/tree-walk.h
+++ b/tree-walk.h
@@ -13,6 +13,11 @@ struct name_entry {
int pathlen;
};
+static inline int tree_entry_len(const char *name, const unsigned char *sha1)
+{
+ return (char *)sha1 - (char *)name - 1;
+}
+
void update_tree_entry(struct tree_desc *);
const unsigned char *tree_entry_extract(struct tree_desc *, const char **, unsigned int *);
^ permalink raw reply related [flat|nested] 79+ messages in thread
* Re: [PATCH 2/2] Implement a simple delta_base cache
2007-03-18 3:00 ` Nicolas Pitre
@ 2007-03-18 3:31 ` Linus Torvalds
2007-03-18 5:30 ` Julian Phillips
2007-03-18 10:53 ` Robin Rosenberg
0 siblings, 2 replies; 79+ messages in thread
From: Linus Torvalds @ 2007-03-18 3:31 UTC (permalink / raw)
To: Nicolas Pitre; +Cc: Morten Welinder, Junio C Hamano, Git Mailing List
On Sat, 17 Mar 2007, Nicolas Pitre wrote:
>
> Sure. But at this point the reference to compare GIT performance
> against might be GIT itself. And while 1 second is really nice in this
> case, there are some repos where it could be (and has already been
> reported to be) much more.
I'd still like to see the KDE repo, that thing went quiet after it was
supposed to hit sneaker-net..
If it was 30 seconds before to do a "git log" for some individual file,
after the recent optimizations it should hopefully be down to 10. And I
agree that I might be more motivated to try to get it down further if I
could just find a repository where it's that much.
Right now I can can do a "git log" on any file in the kernel archive in
under a second (well, when I say "any file", I started with a script, but
with 22 thousand files I didn't bother to run it for all that long, so I
ended up testing a few random files in addition to the first few hundred
files of "git ls-files", and they are all well under a second).
And that's without the "git diff --quiet" thing that is still in "next",
and that cut down some of the overhead for other reasons (although I
suspect the effect of that will be less when combined with my patches
since the stuff it cut down I probably cut down even more).
I really suspect you'll have a hard time beating "normal" git with the
patches I sent out. I'm sure it's quite possible - don't get me wrong - I
just suspect it won't be spectacular, and it will be a lot of work.
Linus
^ permalink raw reply [flat|nested] 79+ messages in thread
* Re: [PATCH 2/2] Implement a simple delta_base cache
2007-03-18 3:31 ` Linus Torvalds
@ 2007-03-18 5:30 ` Julian Phillips
2007-03-18 17:23 ` Linus Torvalds
2007-03-18 10:53 ` Robin Rosenberg
1 sibling, 1 reply; 79+ messages in thread
From: Julian Phillips @ 2007-03-18 5:30 UTC (permalink / raw)
To: Linus Torvalds
Cc: Nicolas Pitre, Morten Welinder, Junio C Hamano, Git Mailing List
[-- Attachment #1: Type: TEXT/PLAIN, Size: 1448 bytes --]
On Sat, 17 Mar 2007, Linus Torvalds wrote:
> On Sat, 17 Mar 2007, Nicolas Pitre wrote:
>>
>> Sure. But at this point the reference to compare GIT performance
>> against might be GIT itself. And while 1 second is really nice in this
>> case, there are some repos where it could be (and has already been
>> reported to be) much more.
>
> I'd still like to see the KDE repo, that thing went quiet after it was
> supposed to hit sneaker-net..
>
> If it was 30 seconds before to do a "git log" for some individual file,
> after the recent optimizations it should hopefully be down to 10. And I
> agree that I might be more motivated to try to get it down further if I
> could just find a repository where it's that much.
In my test repository (which emulates a real repository in terms of
approximate size in terms of commits, branches and tags) "git log f12000"
takes about 15m (using 1.5.0.4). After applying patches 1/2 and 2/2 on
top of master I get ~3m50s. With 3/2 as well it goes down a bit more to
~3m20s.
I've attached the script that generated the repository in case you feel
the urge to try some move time shaving exercises ... ;)
(This is a rather unrealistic repository consisting of a long series of
commits of new binary files, but I don't have access to the repository
that is being approximated until I get back to work on Monday ...)
--
Julian
---
That must be wonderful: I don't understand it at all.
-- Moliere
[-- Attachment #2: mk_large_repo --]
[-- Type: TEXT/PLAIN, Size: 753 bytes --]
#!/bin/bash
# no. of commits branches and tags to make
commits=25000;
branches=900;
tags=8000;
# create a new file of this size (kb) for each commit
commit_size=102;
bs=1024;
large=$1;
((bg = $commits / $branches));
((tg = $commits / $tags));
echo "creating $large";
mkdir $large;
cd $large;
git init-db;
i=0
while [ $i -lt $commits ]; do
dd if=/dev/urandom of=f$i bs=${bs} count=${commit_size} > /dev/null 2>&1
git add f$i;
git commit -m "add t$i";
((ig = $i % $tg));
if [ $ig -eq 0 ]; then
git tag t$i;
echo -n "t";
fi
((ig = $i % $bg));
if [ $ig -eq 0 ]; then
git branch b$i;
echo -n "b";
fi
echo -n "$i ";
((i = $i + 1))
done
echo;
echo "complete.";
^ permalink raw reply [flat|nested] 79+ messages in thread
* Re: [PATCH 2/2] Implement a simple delta_base cache
2007-03-18 1:14 ` Morten Welinder
2007-03-18 1:29 ` Linus Torvalds
@ 2007-03-18 6:28 ` Avi Kivity
1 sibling, 0 replies; 79+ messages in thread
From: Avi Kivity @ 2007-03-18 6:28 UTC (permalink / raw)
To: Morten Welinder
Cc: Linus Torvalds, Junio C Hamano, Nicolas Pitre, Git Mailing List
Morten Welinder wrote:
>> samples % app name symbol name
>> 41527 15.6550 git strlen
>
> Almost 16% in strlen? Ugh!
>
> That's a lot of strings, or perhaps very long strings. Or a profiling
> bug.
>
Or maybe strlen() is the first function to touch the page/cacheline.
--
Do not meddle in the internals of kernels, for they are subtle and quick to panic.
^ permalink raw reply [flat|nested] 79+ messages in thread
* Re: [PATCH 2/2] Implement a simple delta_base cache
2007-03-18 1:13 ` Nicolas Pitre
@ 2007-03-18 7:47 ` Junio C Hamano
0 siblings, 0 replies; 79+ messages in thread
From: Junio C Hamano @ 2007-03-18 7:47 UTC (permalink / raw)
To: Nicolas Pitre; +Cc: Linus Torvalds, Git Mailing List
Nicolas Pitre <nico@cam.org> writes:
> A malloc() + memcpy() will always be faster than mmap() + malloc() +
> inflate(). If the data is already there it is certainly better to copy
> it straight away.
I do not know if there is mmap() cost involved, but you are
correct to point out that my aversion to malloc() cost was
unfounded. We need to allocate anyway, and memcpy() should of
course be cheaper than inflate().
> With the patch below I can do 'git log drivers/scsi/ > /dev/null' about
> 7% faster. I bet it might be even more on those platforms with bad
> mmap() support.
Wonderful. I was going to nitpick but you even took care of the
convention of returning a buffer with one extra byte that
terminates the contents with NUL. Perfect.
^ permalink raw reply [flat|nested] 79+ messages in thread
* Re: [PATCH 3/2] Avoid unnecessary strlen() calls
2007-03-18 3:06 ` [PATCH 3/2] Avoid unnecessary strlen() calls Linus Torvalds
@ 2007-03-18 9:45 ` Junio C Hamano
2007-03-18 15:54 ` Linus Torvalds
0 siblings, 1 reply; 79+ messages in thread
From: Junio C Hamano @ 2007-03-18 9:45 UTC (permalink / raw)
To: Linus Torvalds; +Cc: Nicolas Pitre, Morten Welinder, Git Mailing List
Linus Torvalds <torvalds@linux-foundation.org> writes:
> This shaves off another ~5-10% from some loads that are very tree
> intensive (notably doing commit filtering by a pathspec).
>
> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>"
With your 256-entry cache, Nico's reusing objects out of delta
base cache, and this strlen() patch
git blame -C block/ll_rw_blk.c
gets these numbers:
(v1.5.0)
14.71user 0.26system 0:15.07elapsed 99%CPU (0avgtext+0avgdata 0maxresident)k
0inputs+0outputs (0major+93622minor)pagefaults 0swaps
(master + three patches)
8.94user 0.14system 0:09.10elapsed 99%CPU (0avgtext+0avgdata 0maxresident)k
0inputs+0outputs (0major+40075minor)pagefaults 0swaps
Just for fun, these are the same for the kernel history with tglx-history
repository's history grafted behind it, i.e. with this grafts file:
$ cat .git/info/grafts
1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 e7e173af42dbf37b1d946f9ee00219cb3b2bea6a
(v1.5.0)
73.80user 2.57system 1:16.40elapsed 99%CPU (0avgtext+0avgdata 0maxresident)k
0inputs+0outputs (0major+773077minor)pagefaults 0swaps
(master + three patches)
65.14user 0.40system 1:05.55elapsed 99%CPU (0avgtext+0avgdata 0maxresident)k
0inputs+0outputs (0major+125052minor)pagefaults 0swaps
In either case, it is showing drastic reduction of minor faults.
^ permalink raw reply [flat|nested] 79+ messages in thread
* Re: [PATCH 2/2] Implement a simple delta_base cache
2007-03-18 3:31 ` Linus Torvalds
2007-03-18 5:30 ` Julian Phillips
@ 2007-03-18 10:53 ` Robin Rosenberg
2007-03-18 17:34 ` Linus Torvalds
1 sibling, 1 reply; 79+ messages in thread
From: Robin Rosenberg @ 2007-03-18 10:53 UTC (permalink / raw)
To: Linus Torvalds
Cc: Nicolas Pitre, Morten Welinder, Junio C Hamano, Git Mailing List
söndag 18 mars 2007 04:31 skrev Linus Torvalds:
> I'd still like to see the KDE repo, that thing went quiet after it was
> supposed to hit sneaker-net..
>
> If it was 30 seconds before to do a "git log" for some individual file,
> after the recent optimizations it should hopefully be down to 10. And I
> agree that I might be more motivated to try to get it down further if I
> could just find a repository where it's that much.
I don't have the KDE repo, but I do have an Eclipse import. Without your
patches I get (hot cache)
# time git log -- org.eclipse.core.resources/src/org/eclipse/core/resources/ >/dev/null
65.10user 0.50system 1:12.44elapsed 90%CPU (0avgtext+0avgdata 0maxresident)k
0inputs+0outputs (0major+80242minor)pagefaults 0swaps
With patch 1&2 (hot cache)
# time ~/SW/GIT/git-log -- org.eclipse.core.resources/src/org/eclipse/core/resources/ >/dev/null
27.51user 0.21system 0:28.23elapsed 98%CPU (0avgtext+0avgdata 0maxresident)k
0inputs+0outputs (0major+80266minor)pagefaults 0swaps
That's quite an improvement The eclipse repo is about 140k commits in the master branch and
has a 3GB pack file (fromcvs import).
-- robin
^ permalink raw reply [flat|nested] 79+ messages in thread
* Re: [PATCH 3/2] Avoid unnecessary strlen() calls
2007-03-18 9:45 ` Junio C Hamano
@ 2007-03-18 15:54 ` Linus Torvalds
2007-03-18 15:57 ` Linus Torvalds
` (2 more replies)
0 siblings, 3 replies; 79+ messages in thread
From: Linus Torvalds @ 2007-03-18 15:54 UTC (permalink / raw)
To: Junio C Hamano; +Cc: Nicolas Pitre, Morten Welinder, Git Mailing List
On Sun, 18 Mar 2007, Junio C Hamano wrote:
>
> git blame -C block/ll_rw_blk.c
>
> Just for fun, these are the same for the kernel history with tglx-history
> repository's history grafted behind it, i.e. with this grafts file:
>
> $ cat .git/info/grafts
> 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 e7e173af42dbf37b1d946f9ee00219cb3b2bea6a
>
> (v1.5.0)
> 73.80user 2.57system 1:16.40elapsed 99%CPU (0avgtext+0avgdata 0maxresident)k
> 0inputs+0outputs (0major+773077minor)pagefaults 0swaps
>
> (master + three patches)
> 65.14user 0.40system 1:05.55elapsed 99%CPU (0avgtext+0avgdata 0maxresident)k
> 0inputs+0outputs (0major+125052minor)pagefaults 0swaps
>
> In either case, it is showing drastic reduction of minor faults.
That's an interesting test-case (and I get 53 seconds, nyaah, nyaah ;)
However, it's almost totally *not* about object access any more with my
patches. All the top profiling hits are about generating the patches and
assigning blame:
samples % image name app name symbol name
470352 15.5813 git git xdl_hash_record
298683 9.8944 git git cmp_suspect
225156 7.4587 git git assign_blame
221308 7.3312 libc-2.5.so libc-2.5.so memcpy
177621 5.8840 libc-2.5.so libc-2.5.so memchr
163571 5.4186 vmlinux vmlinux __copy_user_nocache
129301 4.2833 git git xdl_prepare_ctx
99009 3.2799 libc-2.5.so libc-2.5.so _int_malloc
83899 2.7793 git git xdiff_outf
80588 2.6696 libz.so.1.2.3 libz.so.1.2.3 (no symbols)
..
so as you can see, libz is down in the 2.5% range, and strlen and the tree
accessor functions are totally un the noise.
So it looks like it *used* to be somewhat of a problem (the object access
itself must have been about 10 seconds, since that got shaved off the
time), but realistically, if you want to speed up "git blame", we can
totally ignore the git object data structures, an dconcentrate on xdiff
and on blame itself (cmp_suspect and assign_blame probably have some nasty
O(n^2) behaviour or something like that, that could hopefully be fixed
fairly easily. The xdl hashing is a different thing, and I don't think
it's necessarily easy to fix that one..)
Linus
^ permalink raw reply [flat|nested] 79+ messages in thread
* Re: [PATCH 3/2] Avoid unnecessary strlen() calls
2007-03-18 15:54 ` Linus Torvalds
@ 2007-03-18 15:57 ` Linus Torvalds
2007-03-18 21:38 ` Shawn O. Pearce
2007-03-20 3:05 ` Johannes Schindelin
2007-03-20 3:16 ` Junio C Hamano
2 siblings, 1 reply; 79+ messages in thread
From: Linus Torvalds @ 2007-03-18 15:57 UTC (permalink / raw)
To: Junio C Hamano; +Cc: Nicolas Pitre, Morten Welinder, Git Mailing List
On Sun, 18 Mar 2007, Linus Torvalds wrote:
>
> That's an interesting test-case (and I get 53 seconds, nyaah, nyaah ;)
Btw, it's also an example of why the incremental blame is so much nicer.
No way would I want to wait 53 seconds to get the whole blame. But doing
git gui blame HEAD block/ll_rw_blk.c
(the "git gui" command line is a bit unwieldly) you get something quite
usable!
Of course, the git gui blame colorization is clearly done by somebody who
is still actively popping LSD with both fists and didn't realize that the
60's are long done, but that's another issue.
Linus
^ permalink raw reply [flat|nested] 79+ messages in thread
* Re: [PATCH 2/2] Implement a simple delta_base cache
2007-03-18 5:30 ` Julian Phillips
@ 2007-03-18 17:23 ` Linus Torvalds
0 siblings, 0 replies; 79+ messages in thread
From: Linus Torvalds @ 2007-03-18 17:23 UTC (permalink / raw)
To: Julian Phillips
Cc: Nicolas Pitre, Morten Welinder, Junio C Hamano, Git Mailing List
On Sun, 18 Mar 2007, Julian Phillips wrote:
>
> (This is a rather unrealistic repository consisting of a long series of
> commits of new binary files, but I don't have access to the repository that is
> being approximated until I get back to work on Monday ...)
This is a *horrible* test repo.
Is this actually really trying to approximate anything you work with? If
so, please check whether you have cyanide or some other effective poison
to kill all your cow-orkers - it's really doing them a favor - and then do
the honorable thing yourself? Use something especially painful on whoever
came up with the idea to track 25000 files in a single directory.
I'll see what the profile is, but even without the repo full generated
yet, I can already tell you that you should *not* put tens of thousands of
files in a single directory like this.
It's not only usually horribly bad quite independently of any SCM issues
(ie most filesystems will have some bad performance behaviour with things
like this - if only because "readdir()" will inevitably be slow).
And for git it means that you lose all ability to efficiently prune away
the parts of the tree that you don't care about. git will always end up
working with a full linear filemanifest instead of a nice collection of
recursive trees, and a lot of the nice tree-walking optimizations that git
has will just end up being no-ops: each tree is always one *huge*
manifest.
So it's not that git cannot handle it, it's that a lot of the nice things
that make git really efficient simply won't trigger for your repository.
In short: avoiding tens of thousands of files in a single directory is
*always* a good idea. With or without git.
(Again, SCM's that are really just "one file at a time" like CVS,
won't care as much. They never really track all files anyway, so while
they are limited by potential filesystem performance bottlenecks, they
won't have the fundamental issue of tracking 25,000 files..)
Linus
^ permalink raw reply [flat|nested] 79+ messages in thread
* Re: [PATCH 2/2] Implement a simple delta_base cache
2007-03-18 10:53 ` Robin Rosenberg
@ 2007-03-18 17:34 ` Linus Torvalds
2007-03-18 18:29 ` Robin Rosenberg
0 siblings, 1 reply; 79+ messages in thread
From: Linus Torvalds @ 2007-03-18 17:34 UTC (permalink / raw)
To: Robin Rosenberg
Cc: Nicolas Pitre, Morten Welinder, Junio C Hamano, Git Mailing List
On Sun, 18 Mar 2007, Robin Rosenberg wrote:
>
> I don't have the KDE repo, but I do have an Eclipse import.
>
> The eclipse repo is about 140k commits in the master branch and
> has a 3GB pack file (fromcvs import).
Do you happen to have a fast internet connection that you can expose this
thing on?
3GB will take me a while to download, but it sounds like a great
test-case. A 3GB pack-file is what we're supposed to be able to handle
fairly comfortably right now, so it sounds like the ideal project to do
performance testing on.
Linus
^ permalink raw reply [flat|nested] 79+ messages in thread
* Re: [PATCH 2/2] Implement a simple delta_base cache
2007-03-18 17:34 ` Linus Torvalds
@ 2007-03-18 18:29 ` Robin Rosenberg
2007-03-18 21:25 ` Shawn O. Pearce
2007-03-19 13:16 ` David Brodsky
0 siblings, 2 replies; 79+ messages in thread
From: Robin Rosenberg @ 2007-03-18 18:29 UTC (permalink / raw)
To: Linus Torvalds
Cc: Nicolas Pitre, Morten Welinder, Junio C Hamano, Git Mailing List
söndag 18 mars 2007 18:34 skrev Linus Torvalds:
>
> On Sun, 18 Mar 2007, Robin Rosenberg wrote:
> >
> > I don't have the KDE repo, but I do have an Eclipse import.
> >
> > The eclipse repo is about 140k commits in the master branch and
> > has a 3GB pack file (fromcvs import).
>
> Do you happen to have a fast internet connection that you can expose this
> thing on?
Not that fast and it would take me quite a time to move the files to a public
location (it's on my laptop). I'd rather dump it somewhere directly if someone can
provide me with some suitable coordinates.
-- robin
^ permalink raw reply [flat|nested] 79+ messages in thread
* Re: [PATCH 2/2] Implement a simple delta_base cache
2007-03-18 18:29 ` Robin Rosenberg
@ 2007-03-18 21:25 ` Shawn O. Pearce
2007-03-19 13:16 ` David Brodsky
1 sibling, 0 replies; 79+ messages in thread
From: Shawn O. Pearce @ 2007-03-18 21:25 UTC (permalink / raw)
To: Robin Rosenberg
Cc: Linus Torvalds, Nicolas Pitre, Morten Welinder, Junio C Hamano,
Git Mailing List
Robin Rosenberg <robin.rosenberg.lists@dewire.com> wrote:
> söndag 18 mars 2007 18:34 skrev Linus Torvalds:
> >
> > On Sun, 18 Mar 2007, Robin Rosenberg wrote:
> > >
> > > I don't have the KDE repo, but I do have an Eclipse import.
> > >
> > > The eclipse repo is about 140k commits in the master branch and
> > > has a 3GB pack file (fromcvs import).
> >
> > Do you happen to have a fast internet connection that you can expose this
> > thing on?
>
> Not that fast and it would take me quite a time to move the files to a public
> location (it's on my laptop). I'd rather dump it somewhere directly if someone can
> provide me with some suitable coordinates.
I'd like to get a copy of one of these big repos too (KDE, Eclipse).
I probably could get a DVD onto both Internet and Internet2 from a
fast enough pipe that a few folks (e.g. Linus, Nico, Junio) could
pull it down, but I can't offer a public distribution point for
the world.
--
Shawn.
^ permalink raw reply [flat|nested] 79+ messages in thread
* Re: [PATCH 3/2] Avoid unnecessary strlen() calls
2007-03-18 15:57 ` Linus Torvalds
@ 2007-03-18 21:38 ` Shawn O. Pearce
2007-03-18 21:48 ` Linus Torvalds
0 siblings, 1 reply; 79+ messages in thread
From: Shawn O. Pearce @ 2007-03-18 21:38 UTC (permalink / raw)
To: Linus Torvalds
Cc: Junio C Hamano, Nicolas Pitre, Morten Welinder, Git Mailing List
Linus Torvalds <torvalds@linux-foundation.org> wrote:
> Btw, it's also an example of why the incremental blame is so much nicer.
>
> No way would I want to wait 53 seconds to get the whole blame. But doing
>
> git gui blame HEAD block/ll_rw_blk.c
>
> (the "git gui" command line is a bit unwieldly) you get something quite
> usable!
>
> Of course, the git gui blame colorization is clearly done by somebody who
> is still actively popping LSD with both fists and didn't realize that the
> 60's are long done, but that's another issue.
:-)
git-gui is open source. I'd be happy to take a patch. Or,
since that is horribly messy Tcl/Tk code, just a better color
suggestion. :-)
--
Shawn.
^ permalink raw reply [flat|nested] 79+ messages in thread
* Re: [PATCH 3/2] Avoid unnecessary strlen() calls
2007-03-18 21:38 ` Shawn O. Pearce
@ 2007-03-18 21:48 ` Linus Torvalds
0 siblings, 0 replies; 79+ messages in thread
From: Linus Torvalds @ 2007-03-18 21:48 UTC (permalink / raw)
To: Shawn O. Pearce
Cc: Junio C Hamano, Nicolas Pitre, Morten Welinder, Git Mailing List
On Sun, 18 Mar 2007, Shawn O. Pearce wrote:
> Linus Torvalds <torvalds@linux-foundation.org> wrote:
> >
> > Of course, the git gui blame colorization is clearly done by somebody who
> > is still actively popping LSD with both fists and didn't realize that the
> > 60's are long done, but that's another issue.
>
> :-)
>
> git-gui is open source. I'd be happy to take a patch. Or,
> since that is horribly messy Tcl/Tk code, just a better color
> suggestion. :-)
Yeah, the Tcl/Tk part means that I take one look and decide that I have
absolutely zero clue..
Also, I'm not entirely sure what the "right" color is, but the changing
colors do confuse me. Also, maybe I'm some kind of white suburban
house-wife or something, but I prefer calmer pastel colors over the bright
ones you've selected.
I would suggest:
- some special color for "currently selected" (which defaults to being
the first one coming out of the blame thing, of course).
I'd suggest "black text on pale green background", but that may be just
me. Patricia calls the current color "hot pink", and maybe that's
appropriate for a certain segment of the population, but I'm not sure I
want to even *meet* that segment ;)
- some *stable* graduated color for the rest. I don't think it
necessarily needs to be "older" vs "newer", and in fact I'd suggest
just two slightly different shades of gray for the background - just
pick alternating shades for each blame entry that comes in (and leave
un-blamed lines white).
The flickering just makes me go "ooh, I'm really happy I don't have
epilepsy, because otherwise I'd be writhing on the floor every time I
tried to use this tool".
Linus
^ permalink raw reply [flat|nested] 79+ messages in thread
* Re: [PATCH 2/2] Implement a simple delta_base cache
2007-03-18 18:29 ` Robin Rosenberg
2007-03-18 21:25 ` Shawn O. Pearce
@ 2007-03-19 13:16 ` David Brodsky
2007-03-20 6:35 ` Robin Rosenberg
1 sibling, 1 reply; 79+ messages in thread
From: David Brodsky @ 2007-03-19 13:16 UTC (permalink / raw)
To: Robin Rosenberg
Cc: Linus Torvalds, Nicolas Pitre, Morten Welinder, Junio C Hamano,
Git Mailing List
Robin Rosenberg wrote:
> söndag 18 mars 2007 18:34 skrev Linus Torvalds:
>> On Sun, 18 Mar 2007, Robin Rosenberg wrote:
>>> I don't have the KDE repo, but I do have an Eclipse import.
>>>
>>> The eclipse repo is about 140k commits in the master branch and
>>> has a 3GB pack file (fromcvs import).
>> Do you happen to have a fast internet connection that you can expose this
>> thing on?
>
> Not that fast and it would take me quite a time to move the files to a public
> location (it's on my laptop). I'd rather dump it somewhere directly if someone can
> provide me with some suitable coordinates.
I have access to a server with enough disk space and its internet
connection should be something like 10 Mbps (or even faster). I can
provide you anonymous ftp access for upload/download (temporarily) and
http for download (permanent).
Or you can send me a dvd, but that would take some time (at least 1 week
because I'm in the Czech Republic and I don't expect that you are
anywhere near...) and I don't know if postal service can handle such
fragile things like dvds.
This is the smallest thing I can do for you...
David Brodsky
^ permalink raw reply [flat|nested] 79+ messages in thread
* Re: [PATCH 3/2] Avoid unnecessary strlen() calls
2007-03-18 15:54 ` Linus Torvalds
2007-03-18 15:57 ` Linus Torvalds
@ 2007-03-20 3:05 ` Johannes Schindelin
2007-03-20 3:29 ` Shawn O. Pearce
2007-03-20 3:16 ` Junio C Hamano
2 siblings, 1 reply; 79+ messages in thread
From: Johannes Schindelin @ 2007-03-20 3:05 UTC (permalink / raw)
To: Linus Torvalds
Cc: Junio C Hamano, Nicolas Pitre, Morten Welinder, Git Mailing List
Hi,
On Sun, 18 Mar 2007, Linus Torvalds wrote:
> All the top profiling hits are about generating the patches and
> assigning blame:
>
> samples % image name app name symbol name
> 470352 15.5813 git git xdl_hash_record
I felt a little left out in all that performance slashing, and so I
thought maybe, just maybe, a small change in xdl_hash_record() can do
wonders (since it _is_ really simple, but still takes almost a 6th of the
CPU time). I don't have a proper test case setup, so maybe you want to try
this:
-- snipsnap --
[PATCH] xdiff/xutils.c(xdl_hash_record): factor out whitespace handling
Since in at least one use case, xdl_hash_record() takes over 15% of the
CPU time, it makes sense to even micro-optimize it. For many cases, no
whitespace special handling is needed, and in these cases we should not
even bother to check for whitespace in _every_ iteration of the loop.
Signed-off-by: Johannes Schindelin <Johannes.Schindelin@gmx.de>
---
Please do not consider this patch _unless_ it is proven to enhance
the profile statistics substantially.
xdiff/xutils.c | 22 ++++++++++++++++++++--
1 files changed, 20 insertions(+), 2 deletions(-)
diff --git a/xdiff/xutils.c b/xdiff/xutils.c
index 3653864..bf91c0f 100644
--- a/xdiff/xutils.c
+++ b/xdiff/xutils.c
@@ -236,12 +236,13 @@ int xdl_recmatch(const char *l1, long s1, const char *l2, long s2, long flags)
return 0;
}
-unsigned long xdl_hash_record(char const **data, char const *top, long flags) {
+static unsigned long xdl_hash_record_with_whitespace(char const **data,
+ char const *top, long flags) {
unsigned long ha = 5381;
char const *ptr = *data;
for (; ptr < top && *ptr != '\n'; ptr++) {
- if (isspace(*ptr) && (flags & XDF_WHITESPACE_FLAGS)) {
+ if (isspace(*ptr)) {
const char *ptr2 = ptr;
while (ptr + 1 < top && isspace(ptr[1])
&& ptr[1] != '\n')
@@ -270,6 +271,23 @@ unsigned long xdl_hash_record(char const **data, char const *top, long flags) {
}
+unsigned long xdl_hash_record(char const **data, char const *top, long flags) {
+ unsigned long ha = 5381;
+ char const *ptr = *data;
+
+ if (flags & XDF_WHITESPACE_FLAGS)
+ return xdl_hash_record_with_whitespace(data, top, flags);
+
+ for (; ptr < top && *ptr != '\n'; ptr++) {
+ ha += (ha << 5);
+ ha ^= (unsigned long) *ptr;
+ }
+ *data = ptr < top ? ptr + 1: ptr;
+
+ return ha;
+}
+
+
unsigned int xdl_hashbits(unsigned int size) {
unsigned int val = 1, bits = 0;
^ permalink raw reply related [flat|nested] 79+ messages in thread
* Re: [PATCH 3/2] Avoid unnecessary strlen() calls
2007-03-18 15:54 ` Linus Torvalds
2007-03-18 15:57 ` Linus Torvalds
2007-03-20 3:05 ` Johannes Schindelin
@ 2007-03-20 3:16 ` Junio C Hamano
2007-03-20 4:31 ` Linus Torvalds
2 siblings, 1 reply; 79+ messages in thread
From: Junio C Hamano @ 2007-03-20 3:16 UTC (permalink / raw)
To: Linus Torvalds; +Cc: Nicolas Pitre, Morten Welinder, Git Mailing List
Linus Torvalds <torvalds@linux-foundation.org> writes:
> So it looks like it *used* to be somewhat of a problem (the object access
> itself must have been about 10 seconds, since that got shaved off the
> time), but realistically, if you want to speed up "git blame", we can
> totally ignore the git object data structures, an dconcentrate on xdiff
> and on blame itself (cmp_suspect and assign_blame probably have some nasty
> O(n^2) behaviour or something like that,...
With this stupidity-removal patch, it gets down to 7.80user from
8.72user (comparable number of minor faults) for blaming
block/ll_rw_blk.c (without tglx grafts)
diff --git a/builtin-blame.c b/builtin-blame.c
index b51cdc7..104521e 100644
--- a/builtin-blame.c
+++ b/builtin-blame.c
@@ -182,9 +182,8 @@ struct scoreboard {
static int cmp_suspect(struct origin *a, struct origin *b)
{
- int cmp = hashcmp(a->commit->object.sha1, b->commit->object.sha1);
- if (cmp)
- return cmp;
+ if (a->commit != b->commit)
+ return 1;
return strcmp(a->path, b->path);
}
^ permalink raw reply related [flat|nested] 79+ messages in thread
* Re: [PATCH 3/2] Avoid unnecessary strlen() calls
2007-03-20 3:05 ` Johannes Schindelin
@ 2007-03-20 3:29 ` Shawn O. Pearce
2007-03-20 3:40 ` Shawn O. Pearce
0 siblings, 1 reply; 79+ messages in thread
From: Shawn O. Pearce @ 2007-03-20 3:29 UTC (permalink / raw)
To: Johannes Schindelin
Cc: Linus Torvalds, Junio C Hamano, Nicolas Pitre, Morten Welinder,
Git Mailing List
Johannes Schindelin <Johannes.Schindelin@gmx.de> wrote:
> On Sun, 18 Mar 2007, Linus Torvalds wrote:
>
> > All the top profiling hits are about generating the patches and
> > assigning blame:
> >
> > samples % image name app name symbol name
> > 470352 15.5813 git git xdl_hash_record
>
> I felt a little left out in all that performance slashing, and so I
> thought maybe, just maybe, a small change in xdl_hash_record() can do
> wonders (since it _is_ really simple, but still takes almost a 6th of the
> CPU time). I don't have a proper test case setup, so maybe you want to try
> this:
>
> -- snipsnap --
> [PATCH] xdiff/xutils.c(xdl_hash_record): factor out whitespace handling
>
> Since in at least one use case, xdl_hash_record() takes over 15% of the
> CPU time, it makes sense to even micro-optimize it. For many cases, no
> whitespace special handling is needed, and in these cases we should not
> even bother to check for whitespace in _every_ iteration of the loop.
>
> Signed-off-by: Johannes Schindelin <Johannes.Schindelin@gmx.de>
>
> ---
>
> Please do not consider this patch _unless_ it is proven to enhance
> the profile statistics substantially.
This is a massive difference for me. I ran it on git-gui.sh in
the git-gui repository - this is a 6000 line file that has a lot of
revisions, and has been renamed a few times. I applied the patch on
top of current 'master' (v1.5.1-rc1), so I was testing with Linus'
delta_base_cache.
# stock v1.5.1-rc1
$ for a in 1 2 3 4 5;do /usr/bin/time ../lt-blame blame --incremental HEAD git-gui.sh >/dev/null;done
6.27 real 5.31 user 0.55 sys
6.40 real 5.32 user 0.55 sys
6.33 real 5.33 user 0.53 sys
6.67 real 5.32 user 0.55 sys
6.18 real 5.31 user 0.53 sys
# with the above patch
$ for a in 1 2 3 4 5;do /usr/bin/time ../js-blame blame --incremental HEAD git-gui.sh >/dev/null;done
3.57 real 2.87 user 0.51 sys
3.58 real 2.87 user 0.51 sys
3.53 real 2.86 user 0.52 sys
3.61 real 2.86 user 0.51 sys
3.64 real 2.87 user 0.52 sys
For the record, both versions did produce identical output.
Given how small of a change it is, and how much of an improvement
it made, I say apply it.
--
Shawn.
^ permalink raw reply [flat|nested] 79+ messages in thread
* Re: [PATCH 3/2] Avoid unnecessary strlen() calls
2007-03-20 3:29 ` Shawn O. Pearce
@ 2007-03-20 3:40 ` Shawn O. Pearce
2007-03-20 4:11 ` Linus Torvalds
0 siblings, 1 reply; 79+ messages in thread
From: Shawn O. Pearce @ 2007-03-20 3:40 UTC (permalink / raw)
To: Johannes Schindelin
Cc: Linus Torvalds, Junio C Hamano, Nicolas Pitre, Morten Welinder,
Git Mailing List
"Shawn O. Pearce" <spearce@spearce.org> wrote:
> Johannes Schindelin <Johannes.Schindelin@gmx.de> wrote:
> > -- snipsnap --
> > [PATCH] xdiff/xutils.c(xdl_hash_record): factor out whitespace handling
...
> > ---
> >
> > Please do not consider this patch _unless_ it is proven to enhance
> > the profile statistics substantially.
>
> This is a massive difference for me.
...
> # stock v1.5.1-rc1
> $ for a in 1 2 3 4 5;do /usr/bin/time ../lt-blame blame --incremental HEAD git-gui.sh >/dev/null;done
> 6.27 real 5.31 user 0.55 sys
> 6.40 real 5.32 user 0.55 sys
> 6.33 real 5.33 user 0.53 sys
> 6.67 real 5.32 user 0.55 sys
> 6.18 real 5.31 user 0.53 sys
>
> # with the above patch
> $ for a in 1 2 3 4 5;do /usr/bin/time ../js-blame blame --incremental HEAD git-gui.sh >/dev/null;done
> 3.57 real 2.87 user 0.51 sys
> 3.58 real 2.87 user 0.51 sys
> 3.53 real 2.86 user 0.52 sys
> 3.61 real 2.86 user 0.51 sys
> 3.64 real 2.87 user 0.52 sys
DrNick suggested on #git to try flipping the isspace test around.
This is a smaller change and generated the same ~3.60 seconds run
as Dscho's patch. I like DrNick's version better. ;-)
-->8--
[PATCH] xdiff/xutils.c(xdl_hash_record): factor out whitespace handling
Since in at least one use case, xdl_hash_record() takes over 15%
of the CPU time, it makes sense to even micro-optimize it. For
many cases, no whitespace special handling is needed, and in these
cases we should not even bother to check for whitespace in _every_
iteration of the loop.
Signed-off-by: Johannes Schindelin <Johannes.Schindelin@gmx.de>
Signed-off-by: Shawn O. Pearce <spearce@spearce.org>
---
xdiff/xutils.c | 2 +-
1 files changed, 1 insertions(+), 1 deletions(-)
diff --git a/xdiff/xutils.c b/xdiff/xutils.c
index 3653864..7b1f213 100644
--- a/xdiff/xutils.c
+++ b/xdiff/xutils.c
@@ -241,7 +241,7 @@ unsigned long xdl_hash_record(char const **data, char const *top, long flags) {
char const *ptr = *data;
for (; ptr < top && *ptr != '\n'; ptr++) {
- if (isspace(*ptr) && (flags & XDF_WHITESPACE_FLAGS)) {
+ if ((flags & XDF_WHITESPACE_FLAGS) && isspace(*ptr)) {
const char *ptr2 = ptr;
while (ptr + 1 < top && isspace(ptr[1])
&& ptr[1] != '\n')
--
1.5.1.rc1.595.gd1206
--
Shawn.
^ permalink raw reply related [flat|nested] 79+ messages in thread
* Re: [PATCH 3/2] Avoid unnecessary strlen() calls
2007-03-20 3:40 ` Shawn O. Pearce
@ 2007-03-20 4:11 ` Linus Torvalds
2007-03-20 4:18 ` Shawn O. Pearce
2007-03-20 5:44 ` Junio C Hamano
0 siblings, 2 replies; 79+ messages in thread
From: Linus Torvalds @ 2007-03-20 4:11 UTC (permalink / raw)
To: Shawn O. Pearce
Cc: Johannes Schindelin, Junio C Hamano, Nicolas Pitre,
Morten Welinder, Git Mailing List
On Mon, 19 Mar 2007, Shawn O. Pearce wrote:
>
> DrNick suggested on #git to try flipping the isspace test around.
> This is a smaller change and generated the same ~3.60 seconds run
> as Dscho's patch. I like DrNick's version better. ;-)
For me, the result seems to be in the noise.
It may be due to running on Core 2. It's not very sensitive to
micro-optimizations like this. It definitely makes sense to test the
*stable* test first, since that will help branch prediction (the
"isspace()" test is *not* very predictable), so I don't disagree with the
patch, but I suspect it depends a lot on the microarchitecture just how
much it matters.
Do you perhaps have a P4? It has a very bad branch mispredict penalty, so
putting the predictable branch first could explain the big difference you
see..
Dscho's bigger patch probably helps more on an in-order architecture, and
should be equally good on a P4 (or Opteron). On Core 2, neither of the
patches seem to make a huge difference.
Linus
^ permalink raw reply [flat|nested] 79+ messages in thread
* Re: [PATCH 3/2] Avoid unnecessary strlen() calls
2007-03-20 4:11 ` Linus Torvalds
@ 2007-03-20 4:18 ` Shawn O. Pearce
2007-03-20 4:45 ` Linus Torvalds
2007-03-20 5:44 ` Junio C Hamano
1 sibling, 1 reply; 79+ messages in thread
From: Shawn O. Pearce @ 2007-03-20 4:18 UTC (permalink / raw)
To: Linus Torvalds
Cc: Johannes Schindelin, Junio C Hamano, Nicolas Pitre,
Morten Welinder, Git Mailing List
Linus Torvalds <torvalds@linux-foundation.org> wrote:
> On Mon, 19 Mar 2007, Shawn O. Pearce wrote:
> >
> > DrNick suggested on #git to try flipping the isspace test around.
> > This is a smaller change and generated the same ~3.60 seconds run
> > as Dscho's patch. I like DrNick's version better. ;-)
>
> For me, the result seems to be in the noise.
>
> It may be due to running on Core 2. It's not very sensitive to
> micro-optimizations like this. It definitely makes sense to test the
> *stable* test first, since that will help branch prediction (the
> "isspace()" test is *not* very predictable), so I don't disagree with the
> patch, but I suspect it depends a lot on the microarchitecture just how
> much it matters.
>
> Do you perhaps have a P4? It has a very bad branch mispredict penalty, so
> putting the predictable branch first could explain the big difference you
> see..
I tested both patches on a PowerPC G4. (Apple PowerBook, 1.5 GHz)
Running on Mac OS X 10.4.8.
Might be more of a Linux<->Darwin thing; perhaps my isspace is
significantly slower than yours is... after all my mmap runs
like a PC from the 1980s... ;-)
--
Shawn.
^ permalink raw reply [flat|nested] 79+ messages in thread
* Re: [PATCH 3/2] Avoid unnecessary strlen() calls
2007-03-20 3:16 ` Junio C Hamano
@ 2007-03-20 4:31 ` Linus Torvalds
2007-03-20 4:39 ` Shawn O. Pearce
0 siblings, 1 reply; 79+ messages in thread
From: Linus Torvalds @ 2007-03-20 4:31 UTC (permalink / raw)
To: Junio C Hamano; +Cc: Nicolas Pitre, Morten Welinder, Git Mailing List
On Mon, 19 Mar 2007, Junio C Hamano wrote:
>
> With this stupidity-removal patch, it gets down to 7.80user from
> 8.72user (comparable number of minor faults) for blaming
> block/ll_rw_blk.c (without tglx grafts)
Yeah, this one works for me too. Even more than for you. For me,
git blame --incremental -C HEAD block/ll_rw_blk.c
takes 6.71s (best of ten) normally, and 4.85 (best of ten again) with your
patch and Nico's one-liner. In fact, that's a much bigger improvement than
I would have expected from the profile, but it may be that you just cut
the data cache footprint down a lot, and thus made other things more
efficient.
(I just double-checked. Nico's one-liner does help, but not nearly as
radically as it did for Nico. The "best of ten" with *just* Nico's
one-liner is 6.22 for me - better than before, but the combination of
Nico's patch and yours is much more dramatic).
Btw, Dscho's slightly more invasive patch seems to *just* edge out Nico's
one-liner for me, with best-of-ten being 6.17s.
The winner is your patch *with* Dscho's slightly more invasive one: 4.69s.
But the difference between the numbers of Dscho's bigger patch and Nico's
one-liner really are totally in the noise. Dscho *just* wins the
best-of-ten both with and without your patch, but in both cases it's
*way* in the noise. For example, while 4.69s was the best for your+Dscho
in my testing, the full series was
0:05.69
0:04.69
0:04.82
0:04.97
0:04.85
0:05.88
0:04.77
0:04.69
0:05.12
0:04.98
so the variability was big enough that I wouldn't say that 0.1s is really
all that meaningful even for "best of ten". I didn't try to make the
machine totally quiescent, I've got xmms playing in the background etc..
But these kinds of things will definitely vary from machine to machine.
It's all good, though.
Linus
^ permalink raw reply [flat|nested] 79+ messages in thread
* Re: [PATCH 3/2] Avoid unnecessary strlen() calls
2007-03-20 4:31 ` Linus Torvalds
@ 2007-03-20 4:39 ` Shawn O. Pearce
2007-03-20 4:57 ` Linus Torvalds
0 siblings, 1 reply; 79+ messages in thread
From: Shawn O. Pearce @ 2007-03-20 4:39 UTC (permalink / raw)
To: Linus Torvalds
Cc: Junio C Hamano, Nicolas Pitre, Morten Welinder, Git Mailing List
Linus Torvalds <torvalds@linux-foundation.org> wrote:
> Btw, Dscho's slightly more invasive patch seems to *just* edge out Nico's
> one-liner for me, with best-of-ten being 6.17s.
Uh, instead of Nico here don't you mean DrNick on #git? He is in
real life Nicholas Miell. Google says he's somewhat active in the
kernel world, so maybe you know him? ;-)
--
Shawn.
^ permalink raw reply [flat|nested] 79+ messages in thread
* Re: [PATCH 3/2] Avoid unnecessary strlen() calls
2007-03-20 4:18 ` Shawn O. Pearce
@ 2007-03-20 4:45 ` Linus Torvalds
0 siblings, 0 replies; 79+ messages in thread
From: Linus Torvalds @ 2007-03-20 4:45 UTC (permalink / raw)
To: Shawn O. Pearce
Cc: Johannes Schindelin, Junio C Hamano, Nicolas Pitre,
Morten Welinder, Git Mailing List
On Tue, 20 Mar 2007, Shawn O. Pearce wrote:
>
> I tested both patches on a PowerPC G4. (Apple PowerBook, 1.5 GHz)
> Running on Mac OS X 10.4.8.
>
> Might be more of a Linux<->Darwin thing; perhaps my isspace is
> significantly slower than yours is... after all my mmap runs
> like a PC from the 1980s... ;-)
No, we do a git-specific isspace().
But yeah, a G4 will explain the thing even more than a P4 would. The G4
really isn't a very good uarch compared to the modern x86 ones. Not
aggressively out-of-order with deep instruction queues and I don't think
it does basically any memop re-ordering at all. I know Apple used to claim
that they were the fastest PC around (both with the G4 and the G5), but
let's face it, they lied.
The closer to in-order you are, the more instruction scheduling in sw
tends to matter.
Linus
^ permalink raw reply [flat|nested] 79+ messages in thread
* Re: [PATCH 3/2] Avoid unnecessary strlen() calls
2007-03-20 4:39 ` Shawn O. Pearce
@ 2007-03-20 4:57 ` Linus Torvalds
0 siblings, 0 replies; 79+ messages in thread
From: Linus Torvalds @ 2007-03-20 4:57 UTC (permalink / raw)
To: Shawn O. Pearce
Cc: Junio C Hamano, Nicolas Pitre, Morten Welinder, Git Mailing List
On Tue, 20 Mar 2007, Shawn O. Pearce wrote:
> Linus Torvalds <torvalds@linux-foundation.org> wrote:
> > Btw, Dscho's slightly more invasive patch seems to *just* edge out Nico's
> > one-liner for me, with best-of-ten being 6.17s.
>
> Uh, instead of Nico here don't you mean DrNick on #git? He is in
> real life Nicholas Miell. Google says he's somewhat active in the
> kernel world, so maybe you know him? ;-)
I actually meant you.
For some reason, I confuse you and Nico. I've done it several times, and
even without any DrNick mention.
Time to take my meds,
Linus
^ permalink raw reply [flat|nested] 79+ messages in thread
* Re: [PATCH 3/2] Avoid unnecessary strlen() calls
2007-03-20 4:11 ` Linus Torvalds
2007-03-20 4:18 ` Shawn O. Pearce
@ 2007-03-20 5:44 ` Junio C Hamano
1 sibling, 0 replies; 79+ messages in thread
From: Junio C Hamano @ 2007-03-20 5:44 UTC (permalink / raw)
To: Linus Torvalds
Cc: Shawn O. Pearce, Johannes Schindelin, Nicolas Pitre,
Morten Welinder, Git Mailing List
Linus Torvalds <torvalds@linux-foundation.org> writes:
> Dscho's bigger patch probably helps more on an in-order architecture, and
> should be equally good on a P4 (or Opteron). On Core 2, neither of the
> patches seem to make a huge difference.
Because hoisting stable test outside loop is always better for
any architecture, I thought picking between Gitte and Gitney
patches is a no brainer, and I didn't bother to compare-bench,
but I got curious.
(plain)
7.89user 0.15system 0:08.08elapsed 99%CPU (0avgtext+0avgdata 0maxresident)k
0inputs+0outputs (0major+41608minor)pagefaults 0swaps
7.93user 0.18system 0:08.14elapsed 99%CPU (0avgtext+0avgdata 0maxresident)k
0inputs+0outputs (0major+41608minor)pagefaults 0swaps
(gitte -- separate function for slow path)
6.98user 0.18system 0:07.17elapsed 100%CPU (0avgtext+0avgdata 0maxresident)k
0inputs+0outputs (0major+41606minor)pagefaults 0swaps
7.14user 0.12system 0:07.26elapsed 100%CPU (0avgtext+0avgdata 0maxresident)k
0inputs+0outputs (0major+41607minor)pagefaults 0swaps
(gitney -- cheap test first before isspace)
7.23user 0.18system 0:07.42elapsed 99%CPU (0avgtext+0avgdata 0maxresident)k
0inputs+0outputs (0major+41608minor)pagefaults 0swaps
7.32user 0.14system 0:07.48elapsed 99%CPU (0avgtext+0avgdata 0maxresident)k
0inputs+0outputs (0major+41607minor)pagefaults 0swaps
So it does not seem to make much difference on Athlon 64x2 either.
Will apply the "stupid hashcmp() removal" and Dscho's patch and
call it a day.
^ permalink raw reply [flat|nested] 79+ messages in thread
* Re: [PATCH 2/2] Implement a simple delta_base cache
2007-03-19 13:16 ` David Brodsky
@ 2007-03-20 6:35 ` Robin Rosenberg
2007-03-20 9:13 ` David Brodsky
0 siblings, 1 reply; 79+ messages in thread
From: Robin Rosenberg @ 2007-03-20 6:35 UTC (permalink / raw)
To: David Brodsky
Cc: Linus Torvalds, Nicolas Pitre, Morten Welinder, Junio C Hamano,
Git Mailing List
Uploaded now.
David Brodsky provides the final location.
Linus: I noted a large extra file that I don't know where it is from. Seems to
be form the first convetsion. Perhaps you wont' need to download it:
ECLIPSE.git/.git/objects/pack_sETUPg
-- robin
^ permalink raw reply [flat|nested] 79+ messages in thread
* Re: [PATCH 2/2] Implement a simple delta_base cache
2007-03-20 6:35 ` Robin Rosenberg
@ 2007-03-20 9:13 ` David Brodsky
2007-03-21 2:37 ` Linus Torvalds
0 siblings, 1 reply; 79+ messages in thread
From: David Brodsky @ 2007-03-20 9:13 UTC (permalink / raw)
To: Robin Rosenberg
Cc: Linus Torvalds, Nicolas Pitre, Morten Welinder, Junio C Hamano,
Git Mailing List
Robin Rosenberg wrote:
> Uploaded now.
>
> David Brodsky provides the final location.
Anonymous ftp at agnes.kajka.koleje.cuni.cz:10000 - it will stay up for
a while, but since it my desktop machine, I don't guarantee anything.
And (hopefully) permanent http://steamer.kajka.koleje.cuni.cz/Eclipse
Enjoy
David
^ permalink raw reply [flat|nested] 79+ messages in thread
* Re: [PATCH 2/2] Implement a simple delta_base cache
2007-03-20 9:13 ` David Brodsky
@ 2007-03-21 2:37 ` Linus Torvalds
2007-03-21 2:54 ` Nicolas Pitre
0 siblings, 1 reply; 79+ messages in thread
From: Linus Torvalds @ 2007-03-21 2:37 UTC (permalink / raw)
To: David Brodsky
Cc: Robin Rosenberg, Nicolas Pitre, Morten Welinder, Junio C Hamano,
Git Mailing List
On Tue, 20 Mar 2007, David Brodsky wrote:
>
> And (hopefully) permanent http://steamer.kajka.koleje.cuni.cz/Eclipse
Ok, thanks, downloaded. Although the pack-file is just 1.7GB for me, not
3.7 like somebody said.
Anyway, doing a
git blame --incremental HEAD -- org.eclipse.debug.ui/plugin.xml > /dev/null
on that thing (picked a random file that got modified in a recent commit)
took something like 12 seconds, so this is certainly a perfectly fine
test-case.
Sadly, "git-gui blame" doesn't work in a bare git repository, so I had to
do an ugly
ln -s . .git
to make git-gui happy, and that worked, and was pretty usable. Still,
12seconds should be something we can improve on.
And yeah, the profile is pretty horrid:
samples % app name symbol name
70307 20.9412 libc-2.5.so strlen
50925 15.1682 libz.so.1.2.3 (no symbols)
24295 7.2364 git tree_entry_interesting
19816 5.9023 libc-2.5.so memcpy
19569 5.8287 git tree_entry_extract
17693 5.2699 vmlinux memcpy_c
17032 5.0730 git assign_blame
16956 5.0504 git get_mode
12401 3.6937 git get_origin
11815 3.5191 git skip_uninteresting
10449 3.1123 git update_tree_entry
10359 3.0855 git find_pack_entry_one
7946 2.3667 git cmp_suspect
4572 1.3618 libc-2.5.so strncmp
...
so I guess we need to find some more strlen's to remove ;)
Linus
^ permalink raw reply [flat|nested] 79+ messages in thread
* Re: [PATCH 2/2] Implement a simple delta_base cache
2007-03-21 2:37 ` Linus Torvalds
@ 2007-03-21 2:54 ` Nicolas Pitre
0 siblings, 0 replies; 79+ messages in thread
From: Nicolas Pitre @ 2007-03-21 2:54 UTC (permalink / raw)
To: Linus Torvalds
Cc: David Brodsky, Robin Rosenberg, Morten Welinder, Junio C Hamano,
Git Mailing List
On Tue, 20 Mar 2007, Linus Torvalds wrote:
>
>
> On Tue, 20 Mar 2007, David Brodsky wrote:
> >
> > And (hopefully) permanent http://steamer.kajka.koleje.cuni.cz/Eclipse
>
> Ok, thanks, downloaded. Although the pack-file is just 1.7GB for me, not
> 3.7 like somebody said.
There is a 1.3GB garbage pack_sETUPg file in eclipse.git/objects/ laying
there, probably resulting from an interrupted index-pack, making the
repository needlessly bigger. It can be safely deleted.
We probably should make git-prune get rid of those automatically.
Nicolas
^ permalink raw reply [flat|nested] 79+ messages in thread
end of thread, other threads:[~2007-03-21 2:54 UTC | newest]
Thread overview: 79+ messages (download: mbox.gz / follow: Atom feed)
-- links below jump to the message on this page --
2007-03-16 1:04 cleaner/better zlib sources? Linus Torvalds
2007-03-16 1:10 ` Shawn O. Pearce
2007-03-16 1:11 ` Jeff Garzik
2007-03-16 1:14 ` Matt Mackall
2007-03-16 1:46 ` Linus Torvalds
2007-03-16 1:54 ` Linus Torvalds
2007-03-16 2:43 ` Davide Libenzi
2007-03-16 2:56 ` Linus Torvalds
2007-03-16 3:16 ` Davide Libenzi
2007-03-16 16:21 ` Linus Torvalds
2007-03-16 16:24 ` Davide Libenzi
2007-03-16 16:35 ` Linus Torvalds
2007-03-16 19:21 ` Davide Libenzi
2007-03-17 0:01 ` Linus Torvalds
2007-03-17 1:11 ` Linus Torvalds
2007-03-17 3:28 ` Nicolas Pitre
2007-03-17 5:19 ` Shawn O. Pearce
2007-03-17 17:55 ` Linus Torvalds
2007-03-17 19:40 ` Linus Torvalds
2007-03-17 19:42 ` [PATCH 1/2] Make trivial wrapper functions around delta base generation and freeing Linus Torvalds
2007-03-17 19:44 ` [PATCH 2/2] Implement a simple delta_base cache Linus Torvalds
2007-03-17 21:45 ` Linus Torvalds
2007-03-17 22:37 ` Junio C Hamano
2007-03-17 23:09 ` Linus Torvalds
2007-03-17 23:54 ` Linus Torvalds
2007-03-18 1:13 ` Nicolas Pitre
2007-03-18 7:47 ` Junio C Hamano
2007-03-17 23:12 ` Junio C Hamano
2007-03-17 23:24 ` Linus Torvalds
2007-03-17 23:52 ` Jon Smirl
2007-03-18 1:14 ` Morten Welinder
2007-03-18 1:29 ` Linus Torvalds
2007-03-18 1:38 ` Nicolas Pitre
2007-03-18 1:55 ` Linus Torvalds
2007-03-18 2:03 ` Nicolas Pitre
2007-03-18 2:20 ` Linus Torvalds
2007-03-18 3:00 ` Nicolas Pitre
2007-03-18 3:31 ` Linus Torvalds
2007-03-18 5:30 ` Julian Phillips
2007-03-18 17:23 ` Linus Torvalds
2007-03-18 10:53 ` Robin Rosenberg
2007-03-18 17:34 ` Linus Torvalds
2007-03-18 18:29 ` Robin Rosenberg
2007-03-18 21:25 ` Shawn O. Pearce
2007-03-19 13:16 ` David Brodsky
2007-03-20 6:35 ` Robin Rosenberg
2007-03-20 9:13 ` David Brodsky
2007-03-21 2:37 ` Linus Torvalds
2007-03-21 2:54 ` Nicolas Pitre
2007-03-18 3:06 ` [PATCH 3/2] Avoid unnecessary strlen() calls Linus Torvalds
2007-03-18 9:45 ` Junio C Hamano
2007-03-18 15:54 ` Linus Torvalds
2007-03-18 15:57 ` Linus Torvalds
2007-03-18 21:38 ` Shawn O. Pearce
2007-03-18 21:48 ` Linus Torvalds
2007-03-20 3:05 ` Johannes Schindelin
2007-03-20 3:29 ` Shawn O. Pearce
2007-03-20 3:40 ` Shawn O. Pearce
2007-03-20 4:11 ` Linus Torvalds
2007-03-20 4:18 ` Shawn O. Pearce
2007-03-20 4:45 ` Linus Torvalds
2007-03-20 5:44 ` Junio C Hamano
2007-03-20 3:16 ` Junio C Hamano
2007-03-20 4:31 ` Linus Torvalds
2007-03-20 4:39 ` Shawn O. Pearce
2007-03-20 4:57 ` Linus Torvalds
2007-03-18 1:44 ` [PATCH 2/2] Implement a simple delta_base cache Linus Torvalds
2007-03-18 6:28 ` Avi Kivity
2007-03-17 22:44 ` Linus Torvalds
2007-03-16 16:35 ` cleaner/better zlib sources? Jeff Garzik
2007-03-16 16:42 ` Matt Mackall
2007-03-16 16:51 ` Linus Torvalds
2007-03-16 17:12 ` Nicolas Pitre
2007-03-16 23:22 ` Shawn O. Pearce
2007-03-16 17:06 ` Nicolas Pitre
2007-03-16 17:51 ` Linus Torvalds
2007-03-16 18:09 ` Nicolas Pitre
2007-03-16 1:33 ` Davide Libenzi
2007-03-16 2:06 ` Davide Libenzi
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