From: Uros Bizjak Date: Thu, 20 Oct 2022 15:51:04 +0000 (+0200) Subject: raid5-cache: use try_cmpxchg in r5l_wake_reclaim X-Git-Url: http://git.maquefel.me/?a=commitdiff_plain;h=9487a0f6855c1a28e4e39d41545cd19ed417c015;p=linux.git 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 Signed-off-by: Uros Bizjak Signed-off-by: Song Liu --- diff --git a/drivers/md/raid5-cache.c b/drivers/md/raid5-cache.c index 832d8566e1656..a63023aae21e2 100644 --- a/drivers/md/raid5-cache.c +++ b/drivers/md/raid5-cache.c @@ -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); }