From: David Sterba <dsterba@suse.cz>
To: Christoph Hellwig <hch@infradead.org>
Cc: dsterba@suse.cz, David Sterba <dsterba@suse.com>,
linux-btrfs@vger.kernel.org,
"Gustavo A . R . Silva" <gustavoars@kernel.org>
Subject: Re: [PATCH] btrfs: add special case to setget helpers for 64k pages
Date: Thu, 8 Jul 2021 16:34:12 +0200 [thread overview]
Message-ID: <20210708143412.GC2610@twin.jikos.cz> (raw)
In-Reply-To: <YOLD3CJjDgiq+kfR@infradead.org>
On Mon, Jul 05, 2021 at 09:33:34AM +0100, Christoph Hellwig wrote:
> On Fri, Jul 02, 2021 at 01:06:30PM +0200, David Sterba wrote:
> > On Fri, Jul 02, 2021 at 08:10:50AM +0100, Christoph Hellwig wrote:
> > > > + if (INLINE_EXTENT_BUFFER_PAGES == 1) { \
> > > > return get_unaligned_le##bits(token->kaddr + oip); \
> > > > + } else { \
> > >
> > > No need for an else after the return and thus no need for all the
> > > reformatting.
> >
> > That leads to worse code, compiler does not eliminate the block that
> > would otherwise be in the else block. Measured on x86_64 with
> > instrumented code to force INLINE_EXTENT_BUFFER_PAGES = 1 this adds
> > +1100 bytes of code and has impact on stack consumption.
> >
> > That the code that is in two branches that do not share any code is
> > maybe not pretty but the compiler did what I expected. The set/get
> > helpers get called a lot and are performance sensitive.
> >
> > This patch pre (original version), post (with dropped else):
> >
> > 1156210 19305 14912 1190427 122a1b pre/btrfs.ko
> > 1157386 19305 14912 1191603 122eb3 post/btrfs.ko
>
> For the obvious trivial patch (see below) I see the following
> difference, which actually makes the simple change smaller:
>
> text data bss dec hex filename
> 1322580 112183 27600 1462363 16505b fs/btrfs/btrfs.o.hch
> 1322832 112183 27600 1462615 165157 fs/btrfs/btrfs.o.dave
This was on x86_64 and without any further changes to the
extent_buffer::pages, right?
I've tested your version with the following diff emulating the single
page that would be on ppc:
--- a/fs/btrfs/extent_io.h
+++ b/fs/btrfs/extent_io.h
@@ -94,7 +94,8 @@ struct extent_buffer {
struct rw_semaphore lock;
- struct page *pages[INLINE_EXTENT_BUFFER_PAGES];
+ struct page *pages[1];
+ /* struct page *pages[INLINE_EXTENT_BUFFER_PAGES]; */
struct list_head release_list;
#ifdef CONFIG_BTRFS_DEBUG
struct list_head leak_list;
diff --git a/fs/btrfs/struct-funcs.c b/fs/btrfs/struct-funcs.c
index 8260f8bb3ff0..4f8e8f7b29d1 100644
--- a/fs/btrfs/struct-funcs.c
+++ b/fs/btrfs/struct-funcs.c
@@ -52,6 +52,8 @@ static bool check_setget_bounds(const struct extent_buffer *eb,
* from 0 to metadata node size.
*/
+#define _INLINE_EXTENT_BUFFER_PAGES 1
...
---
And replacing _INLINE_EXTENT_BUFFER_PAGES in the checks. This leads to
the same result as in my original version with the copied blocks:
text data bss dec hex filename
1161350 19305 14912 1195567 123e2f pre/btrfs.ko
1156090 19305 14912 1190307 1229a3 post/btrfs.ko
DELTA: -5260
ie. compiler properly removed the dead code after evaluating the
conditions. As your change is simpler code I'll take it, tahnks for the
suggestion.
next prev parent reply other threads:[~2021-07-08 14:36 UTC|newest]
Thread overview: 16+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-07-01 16:00 [PATCH] btrfs: add special case to setget helpers for 64k pages David Sterba
2021-07-01 21:57 ` Gustavo A. R. Silva
2021-07-01 23:59 ` Qu Wenruo
2021-07-02 0:09 ` Gustavo A. R. Silva
2021-07-02 0:21 ` Qu Wenruo
2021-07-02 0:39 ` Gustavo A. R. Silva
2021-07-02 0:39 ` Qu Wenruo
2021-07-02 1:09 ` Gustavo A. R. Silva
2021-07-02 10:22 ` David Sterba
2021-07-02 7:10 ` Christoph Hellwig
2021-07-02 11:06 ` David Sterba
2021-07-05 8:33 ` Christoph Hellwig
2021-07-08 14:34 ` David Sterba [this message]
2021-07-14 23:37 ` Gustavo A. R. Silva
2021-07-28 15:32 ` David Sterba
2021-07-28 16:00 ` David Sterba
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