Re: [Patch 1/3] prefetch the mmap_sem in the fault path

[Ray Bryant]

On Thursday 23 February 2006 06:39, Arjan van de Ven wrote:
> On Thu, 2006-02-23 at 07:29 -0500, Jes Sorensen wrote:
> > >>>>> "Arjan" == Arjan van de Ven <arjan@xxxxxxxxxxxxxxx> writes:
> >
> > Arjan> In a micro-benchmark that stresses the pagefault path, the
> > Arjan> down_read_trylock on the mmap_sem showed up quite high on the
> > Arjan> profile. Turns out this lock is bouncing between cpus quite a
> > Arjan> bit and thus is cache-cold a lot. This patch prefetches the
> > Arjan> lock (for write) as early as possible (and before some other
> > Arjan> somewhat expensive operations). With this patch, the
> > Arjan> down_read_trylock basically fell out of the top of profile.
> >
> > Out of curiousity, how big was the box used for testing? It might be
> > worth investigating if anything can be done to reduce the number of
> > times that lock is taken in the first place.
> >
> > After all, what's a pain on a 4-way tends to be an utter nightmare on
> > a 16-way ;(
>
> most of it was done on a 2 way, but some tests were done on a 4-way.
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Could you share your microbenchmark with us (or point to the source) and we 
can give this a try on larger systems?   

Thanks,
-- 
Ray Bryant
AMD Performance Labs                   Austin, Tx
512-602-0038 (o)                 512-507-7807 (c)

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