From: Arjan van de Ven <arjan@xxxxxxxxxxxxxxx>
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@xxxxxxxxxxxxxxx>
Signed-off-by: Andi Kleen <ak@xxxxxxx>
---
arch/x86_64/mm/fault.c | 6 ++++--
1 files changed, 4 insertions(+), 2 deletions(-)
Index: linux/arch/x86_64/mm/fault.c
===================================================================
--- linux.orig/arch/x86_64/mm/fault.c
+++ linux/arch/x86_64/mm/fault.c
@@ -314,11 +314,13 @@ asmlinkage void __kprobes do_page_fault(
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;
-
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