The following commit has been merged into the sched/urgent branch of tip:
Commit-ID: c5105d764e0214bcc4c6d40d7ba231d01b2e9dda
Gitweb: https://git.kernel.org/tip/c5105d764e0214bcc4c6d40d7ba231d01b2e9dda
Author: Zhenzhong Duan <zhenzhong.duan@xxxxxxxxxx>
AuthorDate: Wed, 27 Nov 2019 16:37:28 +08:00
Committer: Ingo Molnar <mingo@xxxxxxxxxx>
CommitterDate: Fri, 29 Nov 2019 08:10:54 +01:00
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@xxxxxxxxxx>
Reviewed-by: Steven Rostedt (VMware) <rostedt@xxxxxxxxxxx>
Cc: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Cc: bsegall@xxxxxxxxxx
Cc: dietmar.eggemann@xxxxxxx
Cc: juri.lelli@xxxxxxxxxx
Cc: mgorman@xxxxxxx
Cc: vincent.guittot@xxxxxxxxxx
Link: https://lkml.kernel.org/r/1574843848-26825-1-git-send-email-zhenzhong.duan@xxxxxxxxxx
Signed-off-by: Ingo Molnar <mingo@xxxxxxxxxx>
---
kernel/sched/clock.c | 6 +++---
1 file changed, 3 insertions(+), 3 deletions(-)
diff --git a/kernel/sched/clock.c b/kernel/sched/clock.c
index 1152259..12bca64 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();
|