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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: Eric Dumazet <edumazet@google.com>
Cc: Paolo Abeni <pabeni@redhat.com>
Signed-off-by: Uros Bizjak <ubizjak@gmail.com>
Link: https://lore.kernel.org/r/20220822143243.2798-1-ubizjak@gmail.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
This commit is contained in:
Uros Bizjak 2022-08-22 16:32:43 +02:00 committed by Jakub Kicinski
parent 2c58a91495
commit b903078097
1 changed files with 2 additions and 2 deletions
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4
include/linux/netdevice.h
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@ -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;
}