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authorZhenzhong Duan <zhenzhong.duan@oracle.com>2019-11-27 16:37:28 +0800
committerIngo Molnar <mingo@kernel.org>2019-11-29 08:10:54 +0100
commitc5105d764e0214bcc4c6d40d7ba231d01b2e9dda (patch)
tree94352a101ff5da87a5813fd7fdc2e3fd98d75feb /kernel/sched/clock.c
parentc2da5bdc66a377f0b82ee959f19f5a6774706b83 (diff)
downloadlinux-c5105d764e0214bcc4c6d40d7ba231d01b2e9dda.tar.bz2
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/clock.c')
-rw-r--r--kernel/sched/clock.c6
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();