From: Arjan van de Ven <arjan@intel.linux.com>
Date: Sat, 25 Mar 2006 15:30:10 +0000 (+0100)
Subject: [PATCH] x86_64: prefetch the mmap_sem in the fault path
X-Git-Tag: v2.6.17-rc1~705
X-Git-Url: http://git.openpandora.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=a9ba9a3b3897561d01e04cd21433746df46548c0;p=pandora-kernel.git

[PATCH] x86_64: prefetch the mmap_sem in the fault path

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.

Signed-off-by: Arjan van de Ven <arjan@linux.intel.com>
Signed-off-by: Andi Kleen <ak@suse.de>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
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