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From:   "Luck, Tony" <tony.luck@intel.com>
To:     "Guilherme G. Piccoli" <gpiccoli@igalia.com>,
        "tglx@linutronix.de" <tglx@linutronix.de>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
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        "dave.hansen@linux.intel.com" <dave.hansen@linux.intel.com>,
        "hpa@zytor.com" <hpa@zytor.com>,
        "Lutomirski, Andy" <luto@kernel.org>,
        "kernel-dev@igalia.com" <kernel-dev@igalia.com>,
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        "Yu, Fenghua" <fenghua.yu@intel.com>,
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        Paul Gofman <pgofman@codeweavers.com>,
        Pavel Machek <pavel@denx.de>,
        Pierre-Loup Griffais <pgriffais@valvesoftware.com>,
        "Melissa Wen" <mwen@igalia.com>
Subject: RE: [PATCH] x86/split_lock: Restore warn mode (and add a new one) to
 avoid userspace regression
Thread-Topic: [PATCH] x86/split_lock: Restore warn mode (and add a new one) to
 avoid userspace regression
Thread-Index: AQHY00XBSghclGVOu0aBjgkf6Dcm5a31R9GQ
Date:   Wed, 28 Sep 2022 20:24:23 +0000
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References: <20220928142109.150263-1-gpiccoli@igalia.com>
In-Reply-To: <20220928142109.150263-1-gpiccoli@igalia.com>
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> So let's revamp the idea of having another option/mode for the split
> lock detector, which is hereby called "seq" (based on the original
> "sequential" naming in [0]). Also introduces a Kconfig option to give
> the option of Linux vendors have a choice what mode should be their
> default. While at it, fix/improve the documentation about bus locking.
>
> [1] https://github.com/doitsujin/dxvk/issues/2938

Why not just use the workaround suggested in that bug report:

   "so manual switching from default setting to split_lock_detect=3Doff hel=
ps as workaround here"

If you add this extra mode, I'm going to argue that the kernel default
should be "seq" rather than "warn". So these game players will need
to add a split_lock_detect=3Doff (or warn) option.

Has a bug report been filed against the God Of War game? Probably worth fix=
ing,
the performance penalty for split lock is only going to get worse as number=
s of
cores keeps increasing.

-Tony