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authorNick Piggin <npiggin@suse.de>2006-10-11 01:21:52 -0700
committerLinus Torvalds <torvalds@g5.osdl.org>2006-10-11 11:14:22 -0700
commitbeed33a816204cb402c69266475b6a60a2433ceb (patch)
tree4eaa7e5a1ccf2960d1478774cdfcab671384accb
parentf33d9bd50478c9a969b65f58feb6b69a3ad478cb (diff)
[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 <npiggin@suse.de> Acked-by: Ingo Molnar <mingo@elte.hu> Cc: Daniel Walker <dwalker@mvista.com> Cc: Hua Zhong <hzhong@gmail.com> Signed-off-by: Andrew Morton <akpm@osdl.org> Signed-off-by: Linus Torvalds <torvalds@osdl.org>
-rw-r--r--include/asm-generic/bitops/sched.h2
-rw-r--r--kernel/sched.c6
2 files changed, 4 insertions, 4 deletions
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
diff --git a/kernel/sched.c b/kernel/sched.c
index 53608a59d6e..094b5687eef 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: