sched/clock: Use try_cmpxchg64 in sched_clock_{local,remote}

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>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lkml.kernel.org/r/20220518184953.3446778-1-ubizjak@gmail.com

diff --git a/kernel/sched/clock.c b/kernel/sched/clock.c
index d9272d9..e374c0c 100644 (file)
--- a/kernel/sched/clock.c
+++ b/kernel/sched/clock.c
@@ -287,7 +287,7 @@ again:
        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 @@ again:
                val = remote_clock;
        }
 
-       if (cmpxchg64(ptr, old_val, val) != old_val)
+       if (!try_cmpxchg64(ptr, &old_val, val))
                goto again;
 
        return val;