diff options
| author | Uros Bizjak <ubizjak@gmail.com> | 2024-10-10 09:10:05 +0200 |
|---|---|---|
| committer | Thomas Gleixner <tglx@linutronix.de> | 2024-10-17 22:02:27 +0200 |
| commit | 87347f148061b48c3495fb61dcbad384760da9cf (patch) | |
| tree | 22e71d32d1db1766b2c65f7b33775b7071c6e071 | |
| parent | 19298f48694987fac843261c84e24834c255b451 (diff) | |
futex: Use atomic64_try_cmpxchg_relaxed() in get_inode_sequence_number()
Optimize get_inode_sequence_number() to use simpler and faster:
!atomic64_try_cmpxchg_relaxed(*ptr, &old, new)
instead of:
atomic64_cmpxchg relaxed(*ptr, old, new) != old
The x86 CMPXCHG instruction returns success in ZF flag, so
this change saves a compare after cmpxchg. The generated
code improves from:
3da: 31 c0 xor %eax,%eax
3dc: f0 48 0f b1 8a 38 01 lock cmpxchg %rcx,0x138(%rdx)
3e3: 00 00
3e5: 48 85 c0 test %rax,%rax
3e8: 48 0f 44 c1 cmove %rcx,%rax
to:
3da: 31 c0 xor %eax,%eax
3dc: f0 48 0f b1 8a 38 01 lock cmpxchg %rcx,0x138(%rdx)
3e3: 00 00
3e5: 48 0f 44 c1 cmove %rcx,%rax
Signed-off-by: Uros Bizjak <ubizjak@gmail.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Reviewed-by: André Almeida <andrealmeid@igalia.com>
Link: https://lore.kernel.org/all/20241010071023.21913-2-ubizjak@gmail.com
| -rw-r--r-- | kernel/futex/core.c | 4 |
1 files changed, 2 insertions, 2 deletions
diff --git a/kernel/futex/core.c b/kernel/futex/core.c index 3146730e55f7..692912bf1252 100644 --- a/kernel/futex/core.c +++ b/kernel/futex/core.c @@ -185,8 +185,8 @@ static u64 get_inode_sequence_number(struct inode *inode) if (WARN_ON_ONCE(!new)) continue; - old = atomic64_cmpxchg_relaxed(&inode->i_sequence, 0, new); - if (old) + old = 0; + if (!atomic64_try_cmpxchg_relaxed(&inode->i_sequence, &old, new)) return old; return new; } |