Commit 9487a0f6 authored by Uros Bizjak's avatar Uros Bizjak Committed by Song Liu
Browse files

raid5-cache: use try_cmpxchg in r5l_wake_reclaim 



Use try_cmpxchg instead of cmpxchg (*ptr, old, new) == old in
r5l_wake_reclaim. 86 CMPXCHG instruction returns success in ZF flag, so
this change saves a compare after cmpxchg (and related move instruction in
front of cmpxchg).

Also, try_cmpxchg implicitly assigns old *ptr value to "old" when cmpxchg
fails. There is no need to re-read the value in the loop.

Note that the value from *ptr should be read using READ_ONCE to prevent
the compiler from merging, refetching or reordering the read.

No functional change intended.

Cc: Song Liu <song@kernel.org>
Signed-off-by: default avatarUros Bizjak <ubizjak@gmail.com>
Signed-off-by: default avatarSong Liu <song@kernel.org>
parent 3bd548e5

drivers/md/raid5-cache.c

+3 −2
Original line number Diff line number Diff line
@@ -1565,11 +1565,12 @@ void r5l_wake_reclaim(struct r5l_log *log, sector_t space) 


	if (!log)

		return;



	target = READ_ONCE(log->reclaim_target);

	do {

		target = log->reclaim_target;

		if (new < target)

			return;

	} while (cmpxchg(&log->reclaim_target, target, new) != target);

	} while (!try_cmpxchg(&log->reclaim_target, &target, new));

	md_wakeup_thread(log->reclaim_thread);

}