The following commit has been merged into the timers/core branch of tip: Commit-ID: 915d4ad3830aa1a2dafda9b737749fb410cb9790 Gitweb: https://git.kernel.org/tip/915d4ad3830aa1a2dafda9b737749fb410cb9790 Author: Uros Bizjak <ubizjak@xxxxxxxxx> AuthorDate: Mon, 16 Jan 2023 17:53:37 +01:00 Committer: Thomas Gleixner <tglx@xxxxxxxxxxxxx> CommitterDate: Mon, 06 Feb 2023 14:22:09 +01:00 posix-timers: Use atomic64_try_cmpxchg() in __update_gt_cputime() Use atomic64_try_cmpxchg() instead of atomic64_cmpxchg() in __update_gt_cputime(). The x86 CMPXCHG instruction returns success in ZF flag, so this change saves a compare after cmpxchg() (and related move instruction in front of cmpxchg()). Also, atomic64_try_cmpxchg() implicitly assigns old *ptr value to "old" when cmpxchg() fails. There is no need to re-read the value in the loop. No functional change intended. Signed-off-by: Uros Bizjak <ubizjak@xxxxxxxxx> Signed-off-by: Thomas Gleixner <tglx@xxxxxxxxxxxxx> Link: https://lore.kernel.org/r/20230116165337.5810-1-ubizjak@xxxxxxxxx --- kernel/time/posix-cpu-timers.c | 13 ++++++------- 1 file changed, 6 insertions(+), 7 deletions(-) diff --git a/kernel/time/posix-cpu-timers.c b/kernel/time/posix-cpu-timers.c index cb925e8..2f5e9b3 100644 --- a/kernel/time/posix-cpu-timers.c +++ b/kernel/time/posix-cpu-timers.c @@ -243,13 +243,12 @@ static void proc_sample_cputime_atomic(struct task_cputime_atomic *at, */ static inline void __update_gt_cputime(atomic64_t *cputime, u64 sum_cputime) { - u64 curr_cputime; -retry: - curr_cputime = atomic64_read(cputime); - if (sum_cputime > curr_cputime) { - if (atomic64_cmpxchg(cputime, curr_cputime, sum_cputime) != curr_cputime) - goto retry; - } + u64 curr_cputime = atomic64_read(cputime); + + do { + if (sum_cputime <= curr_cputime) + return; + } while (!atomic64_try_cmpxchg(cputime, &curr_cputime, sum_cputime)); } static void update_gt_cputime(struct task_cputime_atomic *cputime_atomic,
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