Commit 915d4ad3 authored by Uros Bizjak's avatar Uros Bizjak Committed by Thomas Gleixner
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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: default avatarUros Bizjak <ubizjak@gmail.com>
Signed-off-by: default avatarThomas Gleixner <tglx@linutronix.de>
Link: https://lore.kernel.org/r/20230116165337.5810-1-ubizjak@gmail.com
parent cbdb1f16

kernel/time/posix-cpu-timers.c

+6 −7
Original line number Diff line number Diff line
@@ -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,