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    Subject[tip: locking/core] sched/clock: Use try_cmpxchg64 in sched_clock_{local,remote}
    The following commit has been merged into the locking/core branch of tip:

    Commit-ID: 8491d1bdf5de152f27fc941e2dcdc4e66c950542
    Gitweb: https://git.kernel.org/tip/8491d1bdf5de152f27fc941e2dcdc4e66c950542
    Author: Uros Bizjak <ubizjak@gmail.com>
    AuthorDate: Wed, 18 May 2022 20:49:53 +02:00
    Committer: Peter Zijlstra <peterz@infradead.org>
    CommitterDate: Thu, 19 May 2022 23:46:09 +02:00

    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
    ---
    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 d9272d9..e374c0c 100644
    --- 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;
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