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Subject[PATCH v2] block: Use try_cmpxchg in update_io_ticks
Date
Use try_cmpxchg instead of cmpxchg (*ptr, old, new) == old in
update_io_ticks. x86 CMPXCHG instruction returns success in ZF flag,
so this change saves a compare after cmpxchg (and related
move instruction in front of cmpxchg).

No functional change intended.

Signed-off-by: Uros Bizjak <ubizjak@gmail.com>
Cc: Jens Axboe <axboe@kernel.dk>
---
v2: Split patch from the original big patch
---
block/blk-core.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/block/blk-core.c b/block/blk-core.c
index 27fb1357ad4b..628b965356db 100644
--- a/block/blk-core.c
+++ b/block/blk-core.c
@@ -987,7 +987,7 @@ void update_io_ticks(struct block_device *part, unsigned long now, bool end)
again:
stamp = READ_ONCE(part->bd_stamp);
if (unlikely(time_after(now, stamp))) {
- if (likely(cmpxchg(&part->bd_stamp, stamp, now) == stamp))
+ if (likely(try_cmpxchg(&part->bd_stamp, &stamp, now)))
__part_stat_add(part, io_ticks, end ? now - stamp : 1);
}
if (part->bd_partno) {
--
2.35.3
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