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Message-Id: <20220712150547.5786-1-ubizjak@gmail.com>
Date: Tue, 12 Jul 2022 17:05:47 +0200
From: Uros Bizjak <ubizjak@...il.com>
To: linux-block@...r.kernel.org, linux-kernel@...r.kernel.org
Cc: Uros Bizjak <ubizjak@...il.com>, Jens Axboe <axboe@...nel.dk>
Subject: [PATCH v2] 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 <ubizjak@...il.com>
Cc: Jens Axboe <axboe@...nel.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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