From: Uros Bizjak Date: Thu, 10 Oct 2024 07:10:05 +0000 (+0200) Subject: futex: Use atomic64_try_cmpxchg_relaxed() in get_inode_sequence_number() X-Git-Url: https://www.infradead.org/git/?a=commitdiff_plain;h=87347f148061b48c3495fb61dcbad384760da9cf;p=users%2Fjedix%2Flinux-maple.git 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 Signed-off-by: Thomas Gleixner Reviewed-by: André Almeida Link: https://lore.kernel.org/all/20241010071023.21913-2-ubizjak@gmail.com --- diff --git a/kernel/futex/core.c b/kernel/futex/core.c index 3146730e55f75..692912bf1252c 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; }