From: Nick Piggin Date: Wed, 11 Oct 2006 08:21:52 +0000 (-0700) Subject: [PATCH] sched: likely profiling X-Git-Tag: v2.6.19-rc2~75 X-Git-Url: https://err.no/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=beed33a816204cb402c69266475b6a60a2433ceb;p=linux-2.6 [PATCH] sched: likely profiling This likely profiling is pretty fun. I found a few possible problems in sched.c. This patch may be not measurable, but when I did measure long ago, nooping (un)likely cost a couple of % on scheduler heavy benchmarks, so it all adds up. Tweak some branch hints: - the 2nd 64 bits in the bitmask is likely to be populated, because it contains the first 28 bits (nearly 3/4) of the normal priorities. (ratio of 669669:691 ~= 1000:1). - it isn't unlikely that context switching switches to another process. it might be very rapidly switching to and from the idle process (ratio of 475815:419004 and 471330:423544). Let the branch predictor decide. - preempt_enable seems to be very often called in a nested preempt_disable or with interrupts disabled (ratio of 3567760:87965 ~= 40:1) Signed-off-by: Nick Piggin Acked-by: Ingo Molnar Cc: Daniel Walker Cc: Hua Zhong Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- diff --git a/include/asm-generic/bitops/sched.h b/include/asm-generic/bitops/sched.h index 5ef93a4d00..815bb01480 100644 --- a/include/asm-generic/bitops/sched.h +++ b/include/asm-generic/bitops/sched.h @@ -15,7 +15,7 @@ static inline int sched_find_first_bit(const unsigned long *b) #if BITS_PER_LONG == 64 if (unlikely(b[0])) return __ffs(b[0]); - if (unlikely(b[1])) + if (likely(b[1])) return __ffs(b[1]) + 64; return __ffs(b[2]) + 128; #elif BITS_PER_LONG == 32 diff --git a/kernel/sched.c b/kernel/sched.c index 53608a59d6..094b5687ee 100644 --- a/kernel/sched.c +++ b/kernel/sched.c @@ -1822,14 +1822,14 @@ context_switch(struct rq *rq, struct task_struct *prev, struct mm_struct *mm = next->mm; struct mm_struct *oldmm = prev->active_mm; - if (unlikely(!mm)) { + if (!mm) { next->active_mm = oldmm; atomic_inc(&oldmm->mm_count); enter_lazy_tlb(oldmm, next); } else switch_mm(oldmm, mm, next); - if (unlikely(!prev->mm)) { + if (!prev->mm) { prev->active_mm = NULL; WARN_ON(rq->prev_mm); rq->prev_mm = oldmm; @@ -3491,7 +3491,7 @@ asmlinkage void __sched preempt_schedule(void) * If there is a non-zero preempt_count or interrupts are disabled, * we do not want to preempt the current task. Just return.. */ - if (unlikely(ti->preempt_count || irqs_disabled())) + if (likely(ti->preempt_count || irqs_disabled())) return; need_resched: