Commit aee8960c authored by Uros Bizjak's avatar Uros Bizjak Committed by Jens Axboe
Browse files

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: default avatarUros 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: default avatarJens Axboe <axboe@kernel.dk>
parent 939f9dd0

block/blk-iolatency.c

+5 −7
Original line number Diff line number Diff line
@@ -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);



	if (!atomic_try_cmpxchg(&iolat->scale_cookie, &our_cookie, cur_cookie)) {

		/* Somebody beat us to the punch, just bail. */

	if (old != our_cookie)

		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);

			}

		}