Commit b9030780 authored Aug 22, 2022 by Uros Bizjak Committed by Jakub Kicinski Aug 25, 2022

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>

parent 2c58a914

include/linux/netdevice.h

+2 −2

Original line number	Diff line number	Diff line
		@@ -546,8 +546,8 @@ static inline bool napi_if_scheduled_mark_missed(struct napi_struct *n)
		{
		unsigned long val, new;

		do {
		val = READ_ONCE(n->state);
		do {
		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;
		}