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Message-ID: <172919585078.1442.8524813422073835687.tip-bot2@tip-bot2>
Date: Thu, 17 Oct 2024 20:10:50 -0000
From: "tip-bot2 for Uros Bizjak" <tip-bot2@...utronix.de>
To: linux-tip-commits@...r.kernel.org
Cc: Uros Bizjak <ubizjak@...il.com>, Thomas Gleixner <tglx@...utronix.de>,
andrealmeid@...lia.com, x86@...nel.org, linux-kernel@...r.kernel.org
Subject: [tip: locking/core] futex: Use atomic64_try_cmpxchg_relaxed() in
get_inode_sequence_number()
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@...il.com>
AuthorDate: Thu, 10 Oct 2024 09:10:05 +02:00
Committer: Thomas Gleixner <tglx@...utronix.de>
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@...il.com>
Signed-off-by: Thomas Gleixner <tglx@...utronix.de>
Reviewed-by: André Almeida <andrealmeid@...lia.com>
Link: https://lore.kernel.org/all/20241010071023.21913-2-ubizjak@gmail.com
---
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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