The patch titled
Subject: epoll: use try_cmpxchg in list_add_tail_lockless
has been added to the -mm mm-nonmm-unstable branch. Its filename is
epoll-use-try_cmpxchg-in-list_add_tail_lockless.patch
This patch will shortly appear at
https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/epoll-use-try_cmpxchg-in-list_add_tail_lockless.patch
This patch will later appear in the mm-nonmm-unstable branch at
git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm
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------------------------------------------------------
From: Uros Bizjak <ubizjak@xxxxxxxxx>
Subject: epoll: use try_cmpxchg in list_add_tail_lockless
Date: Thu, 14 Jul 2022 19:32:55 +0200
Use try_cmpxchg instead of cmpxchg (*ptr, old, new) == old in
list_add_tail_lockless. 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.
Link: https://lkml.kernel.org/r/20220714173255.12987-1-ubizjak@xxxxxxxxx
Signed-off-by: Uros Bizjak <ubizjak@xxxxxxxxx>
Cc: Alexander Viro <viro@xxxxxxxxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
fs/eventpoll.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
--- a/fs/eventpoll.c~epoll-use-try_cmpxchg-in-list_add_tail_lockless
+++ a/fs/eventpoll.c
@@ -1065,7 +1065,7 @@ static inline bool list_add_tail_lockles
* added to the list from another CPU: the winner observes
* new->next == new.
*/
- if (cmpxchg(&new->next, new, head) != new)
+ if (!try_cmpxchg(&new->next, &new, head))
return false;
/*
_
Patches currently in -mm which might be from ubizjak@xxxxxxxxx are
llist-use-try_cmpxchg-in-llist_add_batch-and-llist_del_first.patch
epoll-use-try_cmpxchg-in-list_add_tail_lockless.patch
