linux-kernel - Re: [PATCH v3 2/3] x86/smp native_play_dead: Prefer cpuidle_play_dead() over mwait_play

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Message-ID: <d45e316a-aabd-4d09-9006-d89bbc8fbc3c@intel.com>
Date: Wed, 13 Nov 2024 08:14:08 -0800
From: Dave Hansen <dave.hansen@...el.com>
To: "Gautham R. Shenoy" <gautham.shenoy@....com>,
 Peter Zijlstra <peterz@...radead.org>
Cc: "Rafael J. Wysocki" <rafael@...nel.org>,
 Patryk Wlazlyn <patryk.wlazlyn@...ux.intel.com>, x86@...nel.org,
 linux-kernel@...r.kernel.org, linux-pm@...r.kernel.org,
 rafael.j.wysocki@...el.com, len.brown@...el.com,
 artem.bityutskiy@...ux.intel.com, dave.hansen@...ux.intel.com
Subject: Re: [PATCH v3 2/3] x86/smp native_play_dead: Prefer
 cpuidle_play_dead() over mwait_play_dead()

On 11/13/24 03:41, Gautham R. Shenoy wrote:
> +       /*
> +        * This is ugly. But AMD processors don't prefer MWAIT based
> +        * C-states when processors are offlined.
> +        */
> +       if (boot_cpu_data.x86_vendor == X86_VENDOR_AMD ||
> +           boot_cpu_data.x86_vendor == X86_VENDOR_HYGON)
> +               return -ENODEV;

Can we get an X86_FEATURE for this, please?  Either a positive one:

	X86_FEATURE_MWAIT_OK_FOR_OFFLINE

or a negative one:

	X86_FEATURE_MWAIT_BUSTED_FOR_OFFLINE

... with better names.

Or even a helper.  Because if you add this AMD||HYGON check, it'll be at
_least_ the second one of these for the same logical reason.