From: "André Almeida" <andrealmeid@igalia.com>
To: Uros Bizjak <ubizjak@gmail.com>
Cc: Thomas Gleixner <tglx@linutronix.de>,
Ingo Molnar <mingo@kernel.org>,
Peter Zijlstra <peterz@infradead.org>,
Darren Hart <dvhart@infradead.org>,
linux-kernel@vger.kernel.org, Davidlohr Bueso <dave@stgolabs.net>
Subject: Re: [PATCH 2/2] futex: Use atomic64_try_cmpxchg_relaxed() in get_inode_sequence_number()
Date: Thu, 10 Oct 2024 15:06:58 -0300 [thread overview]
Message-ID: <80c4060f-aea7-4620-afec-feacb234ee22@igalia.com> (raw)
In-Reply-To: <20241010071023.21913-2-ubizjak@gmail.com>
Em 10/10/2024 04:10, Uros Bizjak escreveu:
> 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>
> Cc: Thomas Gleixner <tglx@linutronix.de>
> Cc: Ingo Molnar <mingo@kernel.org>
> Cc: Peter Zijlstra <peterz@infradead.org>
> Cc: Darren Hart <dvhart@infradead.org>
> Cc: Davidlohr Bueso <dave@stgolabs.net>
> Cc: "André Almeida" <andrealmeid@igalia.com>
Reviewed-by: André Almeida <andrealmeid@igalia.com>
next prev parent reply other threads:[~2024-10-10 18:07 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
2024-10-10 7:10 [PATCH 1/2] futex: Use atomic64_inc_return() " Uros Bizjak
2024-10-10 7:10 ` [PATCH 2/2] futex: Use atomic64_try_cmpxchg_relaxed() " Uros Bizjak
2024-10-10 18:06 ` André Almeida [this message]
2024-10-17 20:10 ` [tip: locking/core] " tip-bot2 for Uros Bizjak
2024-10-10 18:05 ` [PATCH 1/2] futex: Use atomic64_inc_return() " André Almeida
2024-10-17 20:10 ` [tip: locking/core] " tip-bot2 for Uros Bizjak
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