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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@gmail.com>
Cc: Jens Axboe <axboe@kernel.dk>
Link: https://lore.kernel.org/r/20220712150547.5786-1-ubizjak@gmail.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>
This commit is contained in:
Uros Bizjak 2022-07-12 17:05:47 +02:00 committed by Jens Axboe
parent f3ec5d1155
commit f4b1e27db4
1 changed files with 2 additions and 8 deletions
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10
block/blk-rq-qos.c
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@ -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;
}