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From: Ingo Molnar <mingo@kernel.org>
To: Uros Bizjak <ubizjak@gmail.com>
Cc: Andrew Cooper <andrew.cooper3@citrix.com>,
	LKML <linux-kernel@vger.kernel.org>,
	Thomas Gleixner <tglx@linutronix.de>,
	Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
	Dave Hansen <dave.hansen@linux.intel.com>,
	x86@kernel.org, "H. Peter Anvin" <hpa@zytor.com>
Subject: Re: [PATCH v2] x86/idle: Remove MFENCEs for X86_BUG_CLFLUSH_MONITOR
Date: Sun, 6 Apr 2025 19:21:35 +0200	[thread overview]
Message-ID: <Z_K4HzutEoEQFSco@gmail.com> (raw)
In-Reply-To: <1640cf43-8125-a562-91f9-9b306b863dc7@gmail.com>


* Uros Bizjak <ubizjak@gmail.com> wrote:

> There is another instance of the same sequence in arch/x86/kernel/smpboot.c:
> 
> 		/*
> 		 * The CLFLUSH is a workaround for erratum AAI65 for
> 		 * the Xeon 7400 series.  It's not clear it is actually
> 		 * needed, but it should be harmless in either case.
> 		 * The WBINVD is insufficient due to the spurious-wakeup
> 		 * case where we return around the loop.
> 		 */
> 		mb();
> 		clflush(md);
> 		mb();
> 		__monitor(md, 0, 0);
> 		mb();
> 		__mwait(eax_hint, 0);

True, but I wouldn't touch that - the shutdown path is not a 
performance critical code path in any fashion, and it's often
difficult to debug on real hardware, so the cost/benefit factor
is abnormally high.

Thanks,

	Ingo

      parent reply	other threads:[~2025-04-06 17:21 UTC|newest]

Thread overview: 9+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2025-04-02 17:24 [PATCH v2] x86/idle: Remove MFENCEs for X86_BUG_CLFLUSH_MONITOR Andrew Cooper
2025-04-02 17:35 ` Dave Hansen
2025-04-02 20:04   ` Ingo Molnar
2025-04-02 19:35 ` [tip: x86/mm] x86/idle: Remove MFENCEs for X86_BUG_CLFLUSH_MONITOR in mwait_idle_with_hints() and prefer_mwait_c1_over_halt() tip-bot2 for Andrew Cooper
2025-04-02 20:32 ` tip-bot2 for Andrew Cooper
2025-04-04 14:14 ` [PATCH v2] x86/idle: Remove MFENCEs for X86_BUG_CLFLUSH_MONITOR Uros Bizjak
2025-04-04 14:16   ` Andrew Cooper
2025-04-04 14:49     ` Uros Bizjak
2025-04-06 17:21   ` Ingo Molnar [this message]

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