From f68e14805085972b4e0b0ab684af37f713b9c262 Mon Sep 17 00:00:00 2001 From: "Michael S. Tsirkin" Date: Mon, 21 Sep 2009 17:03:52 -0700 Subject: [PATCH] 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 Signed-off-by: Michael S. Tsirkin Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- mm/mmu_context.c | 9 ++++++--- 1 file 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); } /*