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| author | Uros Bizjak <ubizjak@gmail.com> | 2023-05-09 17:02:55 +0200 |
|---|---|---|
| committer | Ingo Molnar <mingo@kernel.org> | 2023-10-10 10:14:27 +0200 |
| commit | 4fbf8b136ded943f8661cf48270482ad1f5ce7bd (patch) | |
| tree | 6791e499a8533413fffe2b4d0b59f04e2aa1f8f1 /lib/rcuref.c | |
| parent | ad0a2e4c2f20510d7e3f2bc110cf74f8578547f0 (diff) | |
| download | linux-4fbf8b136ded943f8661cf48270482ad1f5ce7bd.tar.gz | |
locking/atomics: Use atomic_try_cmpxchg_release() to micro-optimize rcuref_put_slowpath()
Use atomic_try_cmpxchg() instead of atomic_cmpxchg(*ptr, old, new) == old
in rcuref_put_slowpath(). On x86 the CMPXCHG instruction returns success in the
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.
Signed-off-by: Uros Bizjak <ubizjak@gmail.com>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Paul E. McKenney <paulmck@kernel.org>
Link: https://lore.kernel.org/r/20230509150255.3691-1-ubizjak@gmail.com
Diffstat (limited to 'lib/rcuref.c')
| -rw-r--r-- | lib/rcuref.c | 2 |
1 files changed, 1 insertions, 1 deletions
diff --git a/lib/rcuref.c b/lib/rcuref.c index 5ec00a4a64d11c..97f300eca927ce 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; /* |