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Subject[PATCH] sched/clock: Use try_cmpxchg64 in sched_clock_{local,remote}
Date
Use try_cmpxchg64 instead of cmpxchg64 (*ptr, old, new) != old in
sched_clock_{local,remote}. x86 cmpxchg returns success in ZF flag,
so this change saves a compare after cmpxchg (and related move
instruction in front of cmpxchg).

Signed-off-by: Uros Bizjak <ubizjak@gmail.com>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Juri Lelli <juri.lelli@redhat.com>
Cc: Vincent Guittot <vincent.guittot@linaro.org>
Cc: Dietmar Eggemann <dietmar.eggemann@arm.com>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Ben Segall <bsegall@google.com>
Cc: Mel Gorman <mgorman@suse.de>
Cc: Daniel Bristot de Oliveira <bristot@redhat.com>
---
Patch requires commits 0aa7be05d83cc584da0782405e8007e351dfb6cc
and c2df0a6af177b6c06a859806a876f92b072dc624 from tip.git
---
kernel/sched/clock.c | 4 ++--
1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/kernel/sched/clock.c b/kernel/sched/clock.c
index d9272d9061a3..e374c0c923da 100644
--- a/kernel/sched/clock.c
+++ b/kernel/sched/clock.c
@@ -287,7 +287,7 @@ notrace static u64 sched_clock_local(struct sched_clock_data *scd)
clock = wrap_max(clock, min_clock);
clock = wrap_min(clock, max_clock);

- if (cmpxchg64(&scd->clock, old_clock, clock) != old_clock)
+ if (!try_cmpxchg64(&scd->clock, &old_clock, clock))
goto again;

return clock;
@@ -349,7 +349,7 @@ notrace static u64 sched_clock_remote(struct sched_clock_data *scd)
val = remote_clock;
}

- if (cmpxchg64(ptr, old_val, val) != old_val)
+ if (!try_cmpxchg64(ptr, &old_val, val))
goto again;

return val;
--
2.35.1
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