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| author | Uros Bizjak <ubizjak@gmail.com> | 2022-07-12 17:44:55 +0200 |
|---|---|---|
| committer | Jens Axboe <axboe@kernel.dk> | 2022-07-12 15:46:03 -0600 |
| commit | 96388f57d2aad9836b2c589181fa1dbaba4066b4 (patch) | |
| tree | 8d55b77e103b15559c7b64e034ca5ea0df21ea0e /block | |
| parent | aee8960c2eae12636040dbf0f04e135273b1612d (diff) | |
| download | lwn-96388f57d2aad9836b2c589181fa1dbaba4066b4.tar.gz lwn-96388f57d2aad9836b2c589181fa1dbaba4066b4.zip | |
blk-cgroup: Use atomic{,64}_try_cmpxchg
Use atomic_try_cmpxchg instead of atomic_cmpxchg (*ptr, old, new) == old
in blkcg_unuse_delay, blkcg_set_delay and blkcg_clear_delay and
atomic64_try_cmpxchg in blkcg_scale_delay. 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, atomic_try_cmpxchg implicitly assigns old *ptr value to "old" when
cmpxchg fails, enabling further code simplifications.
No functional change intended.
Signed-off-by: Uros Bizjak <ubizjak@gmail.com>
Cc: Jens Axboe <axboe@kernel.dk>
Link: https://lore.kernel.org/r/20220712154455.66868-1-ubizjak@gmail.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>
Diffstat (limited to 'block')
| -rw-r--r-- | block/blk-cgroup.c | 2 | ||||
| -rw-r--r-- | block/blk-cgroup.h | 12 |
2 files changed, 5 insertions, 9 deletions
diff --git a/block/blk-cgroup.c b/block/blk-cgroup.c index 27a2d0ca0c70..869af9d72bcf 100644 --- a/block/blk-cgroup.c +++ b/block/blk-cgroup.c @@ -1700,7 +1700,7 @@ static void blkcg_scale_delay(struct blkcg_gq *blkg, u64 now) * everybody is happy with their IO latencies. */ if (time_before64(old + NSEC_PER_SEC, now) && - atomic64_cmpxchg(&blkg->delay_start, old, now) == old) { + atomic64_try_cmpxchg(&blkg->delay_start, &old, now)) { u64 cur = atomic64_read(&blkg->delay_nsec); u64 sub = min_t(u64, blkg->last_delay, now - old); int cur_use = atomic_read(&blkg->use_delay); diff --git a/block/blk-cgroup.h b/block/blk-cgroup.h index d4de0a35e066..d2724d1dd7c9 100644 --- a/block/blk-cgroup.h +++ b/block/blk-cgroup.h @@ -430,12 +430,8 @@ static inline int blkcg_unuse_delay(struct blkcg_gq *blkg) * then check to see if we were the last delay so we can drop the * congestion count on the cgroup. */ - while (old) { - int cur = atomic_cmpxchg(&blkg->use_delay, old, old - 1); - if (cur == old) - break; - old = cur; - } + while (old && !atomic_try_cmpxchg(&blkg->use_delay, &old, old - 1)) + ; if (old == 0) return 0; @@ -458,7 +454,7 @@ static inline void blkcg_set_delay(struct blkcg_gq *blkg, u64 delay) int old = atomic_read(&blkg->use_delay); /* We only want 1 person setting the congestion count for this blkg. */ - if (!old && atomic_cmpxchg(&blkg->use_delay, old, -1) == old) + if (!old && atomic_try_cmpxchg(&blkg->use_delay, &old, -1)) atomic_inc(&blkg->blkcg->css.cgroup->congestion_count); atomic64_set(&blkg->delay_nsec, delay); @@ -475,7 +471,7 @@ static inline void blkcg_clear_delay(struct blkcg_gq *blkg) int old = atomic_read(&blkg->use_delay); /* We only want 1 person clearing the congestion count for this blkg. */ - if (old && atomic_cmpxchg(&blkg->use_delay, old, 0) == old) + if (old && atomic_try_cmpxchg(&blkg->use_delay, &old, 0)) atomic_dec(&blkg->blkcg->css.cgroup->congestion_count); } |