From: Andi Kleen <ak@suse.de>
To: Arjan van de Ven <arjan@intel.linux.com>
Cc: linux-kernel@vger.kernel.org, akpm@osdl.org
Subject: Re: [Patch 1/3] prefetch the mmap_sem in the fault path
Date: Thu, 23 Feb 2006 11:14:52 +0100 [thread overview]
Message-ID: <200602231114.52786.ak@suse.de> (raw)
In-Reply-To: <1140688058.4672.19.camel@laptopd505.fenrus.org>
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.
-Andi
next prev parent reply other threads:[~2006-02-23 10:15 UTC|newest]
Thread overview: 8+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <1140686152.2972.25.camel@laptopd505.fenrus.org>
2006-02-23 9:30 ` [Patch 1/3] prefetch the mmap_sem in the fault path Arjan van de Ven
2006-02-23 9:39 ` Andi Kleen
2006-02-23 9:47 ` Arjan van de Ven
2006-02-23 10:14 ` Andi Kleen [this message]
2006-02-23 12:29 ` Jes Sorensen
2006-02-23 12:39 ` Arjan van de Ven
2006-02-23 4:15 ` Ray Bryant
2006-03-01 0:51 Valerie Henson
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