From: Jan Beulich <jbeulich@suse.com>
To: Uros Bizjak <ubizjak@gmail.com>
Cc: Juergen Gross <jgross@suse.com>,
Stefano Stabellini <sstabellini@kernel.org>,
Oleksandr Tyshchenko <oleksandr_tyshchenko@epam.com>,
xen-devel@lists.xenproject.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH] xen/mcelog: simplify MCE_GETCLEAR_FLAGS using xchg()
Date: Thu, 22 Jan 2026 15:21:53 +0100 [thread overview]
Message-ID: <17b237ae-d3c8-4491-8eb5-6ebb4a25a8fc@suse.com> (raw)
In-Reply-To: <20260122141754.116129-1-ubizjak@gmail.com>
On 22.01.2026 15:17, Uros Bizjak wrote:
> The MCE_GETCLEAR_FLAGS ioctl retrieves xen_mcelog.flags while
> atomically clearing it. This was previously implemented using a
> cmpxchg() loop.
>
> Replace the cmpxchg() loop with a single xchg(), which provides the
> same atomic get-and-clear semantics, avoids retry spinning under
> contention, and simplifies the code.
>
> The code on x86_64 improves from:
>
> 186: 8b 15 00 00 00 00 mov 0x0(%rip),%edx
> 18c: 89 d0 mov %edx,%eax
> 18e: f0 0f b1 0d 00 00 00 lock cmpxchg %ecx,0x0(%rip)
> 195: 00
> 196: 39 c2 cmp %eax,%edx
> 198: 75 ec jne 186 <...>
>
> to just:
>
> 186: 87 05 00 00 00 00 xchg %eax,0x0(%rip)
>
> No functional change intended.
>
> Signed-off-by: Uros Bizjak <ubizjak@gmail.com>
Reviewed-by: Jan Beulich <jbeulich@suse.com>
next prev parent reply other threads:[~2026-01-22 14:21 UTC|newest]
Thread overview: 4+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-01-22 14:17 Uros Bizjak
2026-01-22 14:21 ` Jan Beulich
2026-01-22 14:21 ` Jan Beulich [this message]
2026-01-22 14:22 ` Andrew Cooper
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