2022-07-12 16:36:51

by Uros Bizjak

Subject: [PATCH v2] block: Use try_cmpxchg in update_io_ticks

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 <[email protected]>
Cc: Jens Axboe <[email protected]>
---
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

2022-07-12 20:54:35

by Jens Axboe

Subject: Re: [PATCH v2] block: Use try_cmpxchg in update_io_ticks

On Tue, 12 Jul 2022 17:27:41 +0200, Uros Bizjak wrote:
> 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.
>
> [...]

Applied, thanks!

[1/1] block: Use try_cmpxchg in update_io_ticks
commit: 939f9dd040fe1063d884f8f0f89b037093fe2341

Best regards,
--
Jens Axboe