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blk-iolatency: Use atomic{,64}_try_cmpxchg 

Use atomic_try_cmpxchg instead of atomic_cmpxchg (*ptr, old, new) == old
in check_scale_change and atomic64_try_cmpxchg in blkcg_iolatency_done_bio.
x86 CMPXCHG instruction returns success in ZF flag, so this change saves a
compare after cmpxchg (and related move instruction in front of cmpxchg).

No functional change intended.

Signed-off-by: Uros Bizjak <ubizjak@gmail.com>
Cc: Jens Axboe <axboe@kernel.dk>
Link: https://lore.kernel.org/r/20220712151947.6783-1-ubizjak@gmail.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>
This commit is contained in:
Uros Bizjak 2022-07-12 17:19:47 +02:00 committed by Jens Axboe
parent 939f9dd040
commit aee8960c2e
1 changed files with 5 additions and 7 deletions
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12
block/blk-iolatency.c
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@ -401,7 +401,6 @@ static void check_scale_change(struct iolatency_grp *iolat)
unsigned int cur_cookie;
unsigned int our_cookie = atomic_read(&iolat->scale_cookie);
u64 scale_lat;
unsigned int old;
int direction = 0;
if (lat_to_blkg(iolat)->parent == NULL)
@ -422,11 +421,10 @@ static void check_scale_change(struct iolatency_grp *iolat)
else
return;
old = atomic_cmpxchg(&iolat->scale_cookie, our_cookie, cur_cookie);
/* Somebody beat us to the punch, just bail. */
if (old != our_cookie)
if (!atomic_try_cmpxchg(&iolat->scale_cookie, &our_cookie, cur_cookie)) {
/* Somebody beat us to the punch, just bail. */
return;
}
if (direction < 0 && iolat->min_lat_nsec) {
u64 samples_thresh;
@ -633,8 +631,8 @@ static void blkcg_iolatency_done_bio(struct rq_qos *rqos, struct bio *bio)
window_start = atomic64_read(&iolat->window_start);
if (now > window_start &&
(now - window_start) >= iolat->cur_win_nsec) {
if (atomic64_cmpxchg(&iolat->window_start,
window_start, now) == window_start)
if (atomic64_try_cmpxchg(&iolat->window_start,
&window_start, now))
iolatency_check_latencies(iolat, now);
}
}