| Message ID | 20221020153034.7905-1-ubizjak@gmail.com (mailing list archive) |
|---|---|
| State | Superseded, archived |
| Headers | show |
| Series | raid5-cache: use try_cmpxchg in r5l_wake_reclaim Use try_cmpxchg instead of cmpxchg (*ptr, old, new) == old in r5l_wake_reclaim. x86 CMPXCHG instruction returns success in ZF flag, so this change saves a compare after cmpxchg (and related move instruction | expand |
diff --git a/drivers/md/raid5-cache.c b/drivers/md/raid5-cache.c index 832d8566e165..a63023aae21e 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); }
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: Uros Bizjak <ubizjak@gmail.com> --- drivers/md/raid5-cache.c | 5 +++-- 1 file changed, 3 insertions(+), 2 deletions(-)