Messages in this thread | | | Date | Thu, 29 Nov 2007 18:45:39 -0800 | From | Andrew Morton <> | Subject | Re: [PATCH] Fix kmem_cache_free performance regression in slab |
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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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