2022-07-13 16:15:34

by Uros Bizjak

Subject: [PATCH] ALSA: usb-audio: Use atomic_try_cmpxchg in ep_state_update

Use atomic_try_cmpxchg instead of atomic_cmpxchg (*ptr, old, new) == old in
ep_state_update. 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: Takashi Iwai <[email protected]>
---
sound/usb/endpoint.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/sound/usb/endpoint.c b/sound/usb/endpoint.c
index f9c921683948..0d7b73bf7945 100644
--- a/sound/usb/endpoint.c
+++ b/sound/usb/endpoint.c
@@ -133,7 +133,7 @@ static inline bool ep_state_running(struct snd_usb_endpoint *ep)

static inline bool ep_state_update(struct snd_usb_endpoint *ep, int old, int new)
{
- return atomic_cmpxchg(&ep->state, old, new) == old;
+ return atomic_try_cmpxchg(&ep->state, &old, new);
}

/**
--
2.35.3

2022-07-14 09:12:20

by Takashi Iwai

Subject: Re: [PATCH] ALSA: usb-audio: Use atomic_try_cmpxchg in ep_state_update

On Wed, 13 Jul 2022 17:19:46 +0200,
Uros Bizjak wrote:
>
> Use atomic_try_cmpxchg instead of atomic_cmpxchg (*ptr, old, new) == old in
> ep_state_update. 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: Takashi Iwai <[email protected]>

Thanks, applied.


Takashi