Messages in this thread | | | From | Andi Kleen <> | Subject | Re: [Patch 1/3] prefetch the mmap_sem in the fault path | Date | Thu, 23 Feb 2006 11:14:52 +0100 |
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On Thursday 23 February 2006 10:47, Arjan van de Ven wrote: > On Thu, 2006-02-23 at 10:39 +0100, Andi Kleen wrote: > > On Thursday 23 February 2006 10:30, Arjan van de Ven wrote: > > > In a micro-benchmark that stresses the pagefault path, the down_read_trylock > > > on the mmap_sem showed up quite high on the profile. Turns out this lock is > > > bouncing between cpus quite a bit and thus is cache-cold a lot. This patch > > > prefetches the lock (for write) as early as possible (and before some other > > > somewhat expensive operations). With this patch, the down_read_trylock > > > basically fell out of the top of profile. > > > > It is hard to believe because you effectively didn't do the prefetch > > very early > > all you need is a few dozen cycles though; there's a cr2 move and the > entire notifier inbetween.... neither of those is really cheap.
Ok. I added that patch.
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