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,
|