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Subject[PATCH] netdev: Use try_cmpxchg in napi_if_scheduled_mark_missed
Date
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" <davem@davemloft.net>
Cc: Eric Dumazet <edumazet@google.com>
Cc: Jakub Kicinski <kuba@kernel.org>
Cc: Paolo Abeni <pabeni@redhat.com>
Signed-off-by: Uros Bizjak <ubizjak@gmail.com>
---
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
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