From: Andrew Morton <akpm@linux-foundation.org>
To: Matthew Wilcox <matthew@wil.cx>
Cc: Linus Torvalds <torvalds@linux-foundation.org>,
Pekka Enberg <penberg@cs.helsinki.fi>,
linux-kernel@vger.kernel.org, linux-mm@kvack.org
Subject: Re: [PATCH] Fix kmem_cache_free performance regression in slab
Date: Thu, 29 Nov 2007 18:45:39 -0800 [thread overview]
Message-ID: <20071129184539.ba6342b8.akpm@linux-foundation.org> (raw)
In-Reply-To: <20071129190513.GD2584@parisc-linux.org>
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.
>
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.
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next prev parent reply other threads:[~2007-11-30 2:45 UTC|newest]
Thread overview: 3+ messages / expand[flat|nested] mbox.gz Atom feed top
2007-11-29 19:05 Matthew Wilcox
2007-11-30 2:45 ` Andrew Morton [this message]
2007-11-30 9:14 ` Pekka J Enberg
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