linux-kernel - RE: [PATCH V2] x86/split_lock: Add sysctl to control the misery mode

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Message-ID: <SJ1PR11MB60832858BA290E844F6C13E9FC249@SJ1PR11MB6083.namprd11.prod.outlook.com>
Date:   Fri, 14 Oct 2022 18:26:50 +0000
From:   "Luck, Tony" <tony.luck@...el.com>
To:     "Guilherme G. Piccoli" <gpiccoli@...lia.com>,
        "x86@...nel.org" <x86@...nel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
CC:     "tglx@...utronix.de" <tglx@...utronix.de>,
        "mingo@...hat.com" <mingo@...hat.com>,
        "bp@...en8.de" <bp@...en8.de>,
        "dave.hansen@...ux.intel.com" <dave.hansen@...ux.intel.com>,
        "hpa@...or.com" <hpa@...or.com>,
        "Lutomirski, Andy" <luto@...nel.org>,
        "corbet@....net" <corbet@....net>,
        "linux-doc@...r.kernel.org" <linux-doc@...r.kernel.org>,
        "kernel-dev@...lia.com" <kernel-dev@...lia.com>,
        "kernel@...ccoli.net" <kernel@...ccoli.net>,
        Andre Almeida <andrealmeid@...lia.com>,
        "Yu, Fenghua" <fenghua.yu@...el.com>,
        Joshua Ashton <joshua@...ggi.es>,
        Melissa Wen <mwen@...lia.com>,
        Paul Gofman <pgofman@...eweavers.com>,
        Pavel Machek <pavel@...x.de>,
        Pierre-Loup Griffais <pgriffais@...vesoftware.com>,
        "Zebediah Figura" <zfigura@...eweavers.com>
Subject: RE: [PATCH V2] x86/split_lock: Add sysctl to control the misery mode

Looks reasonable.

Are these games multi-threaded with split locks happening on multiple CPUs in parallel?
If they are, then skipping both the 10ms delay and the serialization is needed.

But if split locks are only from one CPU at a time, then possibly it would have
been enough to just have this mitigation skip the:

+		if (msleep_interruptible(10) > 0)
+			return;

Maybe best not to second guess. You have left the default as "mitigation on",
so I'm happy.

-Tony