From f4b1e27db49c8b985b116aa99481b4c6a4342ed4 Mon Sep 17 00:00:00 2001 From: Uros Bizjak Date: Tue, 12 Jul 2022 17:05:47 +0200 Subject: [PATCH] block/rq_qos: Use atomic_try_cmpxchg in atomic_inc_below 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 Cc: Jens Axboe Link: https://lore.kernel.org/r/20220712150547.5786-1-ubizjak@gmail.com Signed-off-by: Jens Axboe --- 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 d3a7569..88f0fe7 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; } -- 2.7.4