Commit f4b1e27d authored by Uros Bizjak's avatar Uros Bizjak Committed by Jens Axboe
Browse files

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: default avatarUros 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: default avatarJens Axboe <axboe@kernel.dk>
parent f3ec5d11

block/blk-rq-qos.c

+2 −8
Original line number Diff line number Diff line
@@ -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;

}