Messages in this thread Patch in this message | | | From | Uros Bizjak <> | Subject | [PATCH v2] block/rq_qos: Use atomic_try_cmpxchg in atomic_inc_below | Date | Tue, 12 Jul 2022 17:05:47 +0200 |
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Use atomic_try_cmpxchg instead of atomic_cmpxchg (*ptr, old, new) == old in atomic_inc_below. 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> --- v2: Split patch from the original big patch --- block/blk-rq-qos.c | 10 ++-------- 1 file changed, 2 insertions(+), 8 deletions(-)
diff --git a/block/blk-rq-qos.c b/block/blk-rq-qos.c index d3a75693adbf..88f0fe7dcf54 100644 --- a/block/blk-rq-qos.c +++ b/block/blk-rq-qos.c @@ -10,16 +10,10 @@ static bool atomic_inc_below(atomic_t *v, unsigned int below) { unsigned int cur = atomic_read(v); - for (;;) { - unsigned int old; - + do { if (cur >= below) return false; - old = atomic_cmpxchg(v, cur, cur + 1); - if (old == cur) - break; - cur = old; - } + } while (!atomic_try_cmpxchg(v, &cur, cur + 1)); return true; } -- 2.35.3
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