lkml.org 
[lkml]   [2007]   [Nov]   [30]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe: [PATCH] Fix kmem_cache_free performance regression in slab
Hi,

On Thu, 29 Nov 2007 12:05:13 -0700 Matthew Wilcox <matthew@wil.cx> wrote:
> > The database performance group have found that half the cycles spent
> > in kmem_cache_free are spent in this one call to BUG_ON. Moving it
> > into the CONFIG_SLAB_DEBUG-only function cache_free_debugcheck() is a
> > performance win of almost 0.5% on their particular benchmark.
> >
> > The call was added as part of commit ddc2e812d592457747c4367fb73edcaa8e1e49ff
> > with the comment that "overhead should be minimal". It may have been
> > minimal at the time, but it isn't now.
> >

On Thu, 29 Nov 2007, Andrew Morton wrote:
> It is worth noting that the offending commit hit mainline in June 2006.
>
> It takes a very long time for some performance regressions to be
> discovered. By which time it is effectively too late to fix it.

What architecture is this? x86_64? I don't think the BUG_ON per se caused
the performance regression but rather the virt_to_head_page() changes to
virt_to_cache() that were added later. But reverting the BUG_ON is fine by
me.

Thanks Matthew and others for tracking this down!

Pekka
-
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/

\
 
 \ /
  Last update: 2007-11-30 10:17    [W:0.056 / U:0.772 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site