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authorMichael S. Tsirkin <mst@redhat.com>2009-09-21 17:03:52 -0700
committerLinus Torvalds <torvalds@linux-foundation.org>2009-09-22 07:17:42 -0700
commitf68e14805085972b4e0b0ab684af37f713b9c262 (patch)
tree6e0cc9e1e3f29b36ec3d7acfaf863cf9bb39ea5b /mm/mmu_context.c
parent3d2d827f5ca5e32816194119d5c980c7e04474a6 (diff)
downloadlinaro-lsk-f68e14805085972b4e0b0ab684af37f713b9c262.tar.gz
mm: reduce atomic use on use_mm fast path
When the mm being switched to matches the active mm, we don't need to increment and then drop the mm count. In a simple benchmark this happens in about 50% of time. Making that conditional reduces contention on that cacheline on SMP systems. Acked-by: Andrea Arcangeli <aarcange@redhat.com> Signed-off-by: Michael S. Tsirkin <mst@redhat.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Diffstat (limited to 'mm/mmu_context.c')
-rw-r--r--mm/mmu_context.c9
1 files changed, 6 insertions, 3 deletions
diff --git a/mm/mmu_context.c b/mm/mmu_context.c
index fd473b51c90..ded9081f402 100644
--- a/mm/mmu_context.c
+++ b/mm/mmu_context.c
@@ -26,13 +26,16 @@ void use_mm(struct mm_struct *mm)
task_lock(tsk);
active_mm = tsk->active_mm;
- atomic_inc(&mm->mm_count);
+ if (active_mm != mm) {
+ atomic_inc(&mm->mm_count);
+ tsk->active_mm = mm;
+ }
tsk->mm = mm;
- tsk->active_mm = mm;
switch_mm(active_mm, mm, tsk);
task_unlock(tsk);
- mmdrop(active_mm);
+ if (active_mm != mm)
+ mmdrop(active_mm);
}
/*