From 0d75e0c420e52b4057a2de274054a5274209a2ae Mon Sep 17 00:00:00 2001 From: Uros Bizjak Date: Tue, 1 Oct 2024 13:45:57 +0200 Subject: [PATCH] locking/osq_lock: Use atomic_try_cmpxchg_release() in osq_unlock() Replace this pattern in osq_unlock(): atomic_cmpxchg(*ptr, old, new) == old ... with the simpler and faster: atomic_try_cmpxchg(*ptr, &old, new) The x86 CMPXCHG instruction returns success in the ZF flag, so this change saves a compare after the CMPXCHG. The code in the fast path of osq_unlock() improves from: 11b: 31 c9 xor %ecx,%ecx 11d: 8d 50 01 lea 0x1(%rax),%edx 120: 89 d0 mov %edx,%eax 122: f0 0f b1 0f lock cmpxchg %ecx,(%rdi) 126: 39 c2 cmp %eax,%edx 128: 75 05 jne 12f <...> to: 12b: 31 d2 xor %edx,%edx 12d: 83 c0 01 add $0x1,%eax 130: f0 0f b1 17 lock cmpxchg %edx,(%rdi) 134: 75 05 jne 13b <...> Signed-off-by: Uros Bizjak Signed-off-by: Peter Zijlstra (Intel) Acked-by: Waiman Long Link: https://lore.kernel.org/r/20241001114606.820277-1-ubizjak@gmail.com --- kernel/locking/osq_lock.c | 3 +-- 1 file changed, 1 insertion(+), 2 deletions(-) diff --git a/kernel/locking/osq_lock.c b/kernel/locking/osq_lock.c index 75a6f6133866d..b4233dc2c2b04 100644 --- a/kernel/locking/osq_lock.c +++ b/kernel/locking/osq_lock.c @@ -215,8 +215,7 @@ void osq_unlock(struct optimistic_spin_queue *lock) /* * Fast path for the uncontended case. */ - if (likely(atomic_cmpxchg_release(&lock->tail, curr, - OSQ_UNLOCKED_VAL) == curr)) + if (atomic_try_cmpxchg_release(&lock->tail, &curr, OSQ_UNLOCKED_VAL)) return; /* -- 2.50.1