* [performance problem] CONFIG_DYNAMIC_FTRACE: Increased kernel build times
@ 2009-10-23 7:45 Ingo Molnar
[not found] ` <520f0cf10910230307k91d0c80sa3d69bcd74d6e1f1@mail.gmail.com>
2009-10-23 13:18 ` Steven Rostedt
0 siblings, 2 replies; 4+ messages in thread
From: Ingo Molnar @ 2009-10-23 7:45 UTC (permalink / raw)
To: Steven Rostedt, Frédéric Weisbecker
Cc: linux-kernel, Thomas Gleixner
Steve,
i did an 64-bit allyesconfig build test (with debug_info disabled), with
and without CONFIG_DYNAMIC_FTRACE set.
The build time results are:
-CONFIG_DYNAMIC_FTRACE: 266.30
+CONFIG_DYNAMIC_FTRACE: 296.07 (+11.2%)
So we get more than 10% build time overhead.
That's quite high - higher than what i remember having measured
originally when the first iteration of the mcount code went in.
This extra overhead comes from the mcount post-processing script
(scripts/recordmcount.pl) that runs objcopy as well and is written in
Perl. I think this whole angle needs to be improved - 10% is way too
high of a price to pay.
Ingo
^ permalink raw reply [flat|nested] 4+ messages in thread
* Re: [performance problem] CONFIG_DYNAMIC_FTRACE: Increased kernel build times
[not found] ` <520f0cf10910230307k91d0c80sa3d69bcd74d6e1f1@mail.gmail.com>
@ 2009-10-23 10:18 ` John Kacur
2009-10-23 10:37 ` Ingo Molnar
0 siblings, 1 reply; 4+ messages in thread
From: John Kacur @ 2009-10-23 10:18 UTC (permalink / raw)
To: Ingo Molnar
Cc: Frederic Weisbecker, Steven Rostedt, Thomas Gleixner, linux-kernel
[-- Attachment #1: Type: TEXT/PLAIN, Size: 879 bytes --]
2009/10/23 Ingo Molnar <mingo@elte.hu> wrote:
>
> Steve,
>
> i did an 64-bit allyesconfig build test (with debug_info disabled), with
> and without CONFIG_DYNAMIC_FTRACE set.
>
> The build time results are:
>
> -CONFIG_DYNAMIC_FTRACE: 266.30
> +CONFIG_DYNAMIC_FTRACE: 296.07 (+11.2%)
>
> So we get more than 10% build time overhead.
>
> That's quite high - higher than what i remember having measured
> originally when the first iteration of the mcount code went in.
>
> This extra overhead comes from the mcount post-processing script
> (scripts/recordmcount.pl) that runs objcopy as well and is written in
> Perl. I think this whole angle needs to be improved - 10% is way too
> high of a price to pay.
Hi Ingo, do you still have the profiling data to share with us?
Was the problem more in objcopy / objdump, rather than in the perl script
itself?
Thanks
John
^ permalink raw reply [flat|nested] 4+ messages in thread
* Re: [performance problem] CONFIG_DYNAMIC_FTRACE: Increased kernel build times
2009-10-23 10:18 ` John Kacur
@ 2009-10-23 10:37 ` Ingo Molnar
0 siblings, 0 replies; 4+ messages in thread
From: Ingo Molnar @ 2009-10-23 10:37 UTC (permalink / raw)
To: John Kacur
Cc: Frederic Weisbecker, Steven Rostedt, Thomas Gleixner, linux-kernel
* John Kacur <jkacur@redhat.com> wrote:
> 2009/10/23 Ingo Molnar <mingo@elte.hu> wrote:
> >
> > Steve,
> >
> > i did an 64-bit allyesconfig build test (with debug_info disabled), with
> > and without CONFIG_DYNAMIC_FTRACE set.
> >
> > The build time results are:
> >
> > -CONFIG_DYNAMIC_FTRACE: 266.30
> > +CONFIG_DYNAMIC_FTRACE: 296.07 (+11.2%)
> >
> > So we get more than 10% build time overhead.
> >
> > That's quite high - higher than what i remember having measured
> > originally when the first iteration of the mcount code went in.
> >
> > This extra overhead comes from the mcount post-processing script
> > (scripts/recordmcount.pl) that runs objcopy as well and is written in
> > Perl. I think this whole angle needs to be improved - 10% is way too
> > high of a price to pay.
>
> Hi Ingo, do you still have the profiling data to share with us? [...]
no finegrained info - i did a perf stat run.
> [...] Was the problem more in objcopy / objdump, rather than in the
> perl script itself?
in top i saw perl pop up most of the time, that's where i'd suspect a
good portion of the overhead.
Ingo
^ permalink raw reply [flat|nested] 4+ messages in thread
* Re: [performance problem] CONFIG_DYNAMIC_FTRACE: Increased kernel build times
2009-10-23 7:45 [performance problem] CONFIG_DYNAMIC_FTRACE: Increased kernel build times Ingo Molnar
[not found] ` <520f0cf10910230307k91d0c80sa3d69bcd74d6e1f1@mail.gmail.com>
@ 2009-10-23 13:18 ` Steven Rostedt
1 sibling, 0 replies; 4+ messages in thread
From: Steven Rostedt @ 2009-10-23 13:18 UTC (permalink / raw)
To: Ingo Molnar; +Cc: Frédéric Weisbecker, linux-kernel, Thomas Gleixner
On Fri, 2009-10-23 at 09:45 +0200, Ingo Molnar wrote:
> Steve,
>
> i did an 64-bit allyesconfig build test (with debug_info disabled), with
> and without CONFIG_DYNAMIC_FTRACE set.
>
> The build time results are:
>
> -CONFIG_DYNAMIC_FTRACE: 266.30
> +CONFIG_DYNAMIC_FTRACE: 296.07 (+11.2%)
>
> So we get more than 10% build time overhead.
>
> That's quite high - higher than what i remember having measured
> originally when the first iteration of the mcount code went in.
>
> This extra overhead comes from the mcount post-processing script
> (scripts/recordmcount.pl) that runs objcopy as well and is written in
> Perl. I think this whole angle needs to be improved - 10% is way too
> high of a price to pay.
Yeah, I know this is quite a hit, and to fix this is on my todo list.
What I plan on doing is checking if libelf is installed, and if it is,
then doing a C program that does the linking and checking. If not, it
defaults back to the perl code.
But I'm bug hunting right now, and that takes a higher priority.
-- Steve
^ permalink raw reply [flat|nested] 4+ messages in thread
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2009-10-23 7:45 [performance problem] CONFIG_DYNAMIC_FTRACE: Increased kernel build times Ingo Molnar
[not found] ` <520f0cf10910230307k91d0c80sa3d69bcd74d6e1f1@mail.gmail.com>
2009-10-23 10:18 ` John Kacur
2009-10-23 10:37 ` Ingo Molnar
2009-10-23 13:18 ` Steven Rostedt
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