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[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>
This commit is contained in:
Arjan van de Ven 2006-03-25 16:30:10 +01:00 committed by Linus Torvalds
parent 4bc32c4d5c
commit a9ba9a3b38
1 changed files with 4 additions and 2 deletions
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6
arch/x86_64/mm/fault.c
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@ -314,11 +314,13 @@ asmlinkage void __kprobes do_page_fault(struct pt_regs *regs,
unsigned long flags;
siginfo_t info;
tsk = current;
mm = tsk->mm;
prefetchw(&mm->mmap_sem);
/* get the address */
__asm__("movq %%cr2,%0":"=r" (address));
tsk = current;
mm = tsk->mm;
info.si_code = SEGV_MAPERR;