Messages in this thread Patch in this message | | | From | Uros Bizjak <> | Subject | [PATCH] atomics: Use atomic_try_cmpxchg_release in rcuref_put_slowpath() | Date | Tue, 9 May 2023 17:02:55 +0200 |
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Use atomic_try_cmpxchg instead of atomic_cmpxchg (*ptr, old, new) == old in rcuref_put_slowpath(). 86 CMPXCHG instruction returns success in ZF flag, so this change saves a compare after cmpxchg. Additionaly, the compiler reorders some code blocks to follow likely/unlikely annotations in the atomic_try_cmpxchg macro, improving the code from
9a: f0 0f b1 0b lock cmpxchg %ecx,(%rbx) 9e: 83 f8 ff cmp $0xffffffff,%eax a1: 74 04 je a7 <rcuref_put_slowpath+0x27> a3: 31 c0 xor %eax,%eax
to
9a: f0 0f b1 0b lock cmpxchg %ecx,(%rbx) 9e: 75 4c jne ec <rcuref_put_slowpath+0x6c> a0: b0 01 mov $0x1,%al
No functional change intended.
Cc: Thomas Gleixner <tglx@linutronix.de> Signed-off-by: Uros Bizjak <ubizjak@gmail.com> --- lib/rcuref.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/lib/rcuref.c b/lib/rcuref.c index 5ec00a4a64d1..97f300eca927 100644 --- a/lib/rcuref.c +++ b/lib/rcuref.c @@ -248,7 +248,7 @@ bool rcuref_put_slowpath(rcuref_t *ref) * require a retry. If this fails the caller is not * allowed to deconstruct the object. */ - if (atomic_cmpxchg_release(&ref->refcnt, RCUREF_NOREF, RCUREF_DEAD) != RCUREF_NOREF) + if (!atomic_try_cmpxchg_release(&ref->refcnt, &cnt, RCUREF_DEAD)) return false; /* -- 2.40.1
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