diff options
| author | Zhenzhong Duan | 2019-11-27 16:37:28 +0800 |
|---|---|---|
| committer | Ingo Molnar | 2019-11-29 08:10:54 +0100 |
| commit | c5105d764e0214bcc4c6d40d7ba231d01b2e9dda (patch) | |
| tree | 94352a101ff5da87a5813fd7fdc2e3fd98d75feb /kernel/sched | |
| parent | c2da5bdc66a377f0b82ee959f19f5a6774706b83 (diff) | |
sched/clock: Use static_branch_likely() with sched_clock_running
sched_clock_running is enabled early at bootup stage and never
disabled. So hint that to the compiler by using static_branch_likely()
rather than static_branch_unlikely().
The branch probability mis-annotation was introduced in the original
commit that converted the plain sched_clock_running flag to a static key:
46457ea464f5 ("sched/clock: Use static key for sched_clock_running")
Steve further notes:
| Looks like the confusion was the moving of the "!":
|
| - if (unlikely(!sched_clock_running))
| + if (!static_branch_unlikely(&sched_clock_running))
|
| Where, it was unlikely that !sched_clock_running would be true, but
| because the "!" was moved outside the "unlikely()" it makes the test
| "likely()". That is, if we added an intermediate step, it would have
| been:
|
| if (!likely(sched_clock_running))
|
| which would have prevented the mistake that this patch fixes.
[ mingo: Edited the changelog. ]
Signed-off-by: Zhenzhong Duan <zhenzhong.duan@oracle.com>
Reviewed-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: bsegall@google.com
Cc: dietmar.eggemann@arm.com
Cc: juri.lelli@redhat.com
Cc: mgorman@suse.de
Cc: vincent.guittot@linaro.org
Link: https://lkml.kernel.org/r/1574843848-26825-1-git-send-email-zhenzhong.duan@oracle.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Diffstat (limited to 'kernel/sched')
| -rw-r--r-- | kernel/sched/clock.c | 6 |
1 files changed, 3 insertions, 3 deletions
diff --git a/kernel/sched/clock.c b/kernel/sched/clock.c index 1152259a4ca0..12bca64dff73 100644 --- a/kernel/sched/clock.c +++ b/kernel/sched/clock.c @@ -370,7 +370,7 @@ u64 sched_clock_cpu(int cpu) if (sched_clock_stable()) return sched_clock() + __sched_clock_offset; - if (!static_branch_unlikely(&sched_clock_running)) + if (!static_branch_likely(&sched_clock_running)) return sched_clock(); preempt_disable_notrace(); @@ -393,7 +393,7 @@ void sched_clock_tick(void) if (sched_clock_stable()) return; - if (!static_branch_unlikely(&sched_clock_running)) + if (!static_branch_likely(&sched_clock_running)) return; lockdep_assert_irqs_disabled(); @@ -460,7 +460,7 @@ void __init sched_clock_init(void) u64 sched_clock_cpu(int cpu) { - if (!static_branch_unlikely(&sched_clock_running)) + if (!static_branch_likely(&sched_clock_running)) return 0; return sched_clock(); |