From beed33a816204cb402c69266475b6a60a2433ceb Mon Sep 17 00:00:00 2001 From: Nick Piggin Date: Wed, 11 Oct 2006 01:21:52 -0700 Subject: [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 --- include/asm-generic/bitops/sched.h | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) (limited to 'include') diff --git a/include/asm-generic/bitops/sched.h b/include/asm-generic/bitops/sched.h index 5ef93a4d009..815bb014806 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 -- cgit v1.2.3