2022-08-22 14:35:41

by Uros Bizjak

Subject: [PATCH] netdev: Use try_cmpxchg in napi_if_scheduled_mark_missed

Use try_cmpxchg instead of cmpxchg (*ptr, old, new) == old in
napi_if_scheduled_mark_missed. x86 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, enabling further code simplifications.

Cc: "David S. Miller" <[email protected]>
Cc: Eric Dumazet <[email protected]>
Cc: Jakub Kicinski <[email protected]>
Cc: Paolo Abeni <[email protected]>
Signed-off-by: Uros Bizjak <[email protected]>
---
include/linux/netdevice.h | 4 ++--
1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/include/linux/netdevice.h b/include/linux/netdevice.h
index 1a3cb93c3dcc..51c916894661 100644
--- a/include/linux/netdevice.h
+++ b/include/linux/netdevice.h
@@ -546,8 +546,8 @@ static inline bool napi_if_scheduled_mark_missed(struct napi_struct *n)
{
unsigned long val, new;

+ val = READ_ONCE(n->state);
do {
- val = READ_ONCE(n->state);
if (val & NAPIF_STATE_DISABLE)
return true;

@@ -555,7 +555,7 @@ static inline bool napi_if_scheduled_mark_missed(struct napi_struct *n)
return false;

new = val | NAPIF_STATE_MISSED;
- } while (cmpxchg(&n->state, val, new) != val);
+ } while (!try_cmpxchg(&n->state, &val, new));

return true;
}
--
2.37.1

2022-08-25 23:58:35

by patchwork-bot+netdevbpf

Subject: Re: [PATCH] netdev: Use try_cmpxchg in napi_if_scheduled_mark_missed

Hello:

This patch was applied to netdev/net-next.git (master)
by Jakub Kicinski <[email protected]>:

On Mon, 22 Aug 2022 16:32:43 +0200 you wrote:
> Use try_cmpxchg instead of cmpxchg (*ptr, old, new) == old in
> napi_if_scheduled_mark_missed. x86 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, enabling further code simplifications.
>
> [...]

Here is the summary with links:
- netdev: Use try_cmpxchg in napi_if_scheduled_mark_missed
https://git.kernel.org/netdev/net-next/c/b9030780971b

You are awesome, thank you!
--
Deet-doot-dot, I am a bot.
https://korg.docs.kernel.org/patchwork/pwbot.html