The following commit has been merged into the locking/core branch of tip: Commit-ID: 87347f148061b48c3495fb61dcbad384760da9cf Gitweb: https://git.kernel.org/tip/87347f148061b48c3495fb61dcbad384760da9cf Author: Uros Bizjak <ubizjak@xxxxxxxxx> AuthorDate: Thu, 10 Oct 2024 09:10:05 +02:00 Committer: Thomas Gleixner <tglx@xxxxxxxxxxxxx> CommitterDate: Thu, 17 Oct 2024 22:02:27 +02:00 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@xxxxxxxxx> Signed-off-by: Thomas Gleixner <tglx@xxxxxxxxxxxxx> Reviewed-by: André Almeida <andrealmeid@xxxxxxxxxx> Link: https://lore.kernel.org/all/20241010071023.21913-2-ubizjak@xxxxxxxxx --- kernel/futex/core.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-) diff --git a/kernel/futex/core.c b/kernel/futex/core.c index 3146730..692912b 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; }
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