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: <20241114115831.GQ6497@noisy.programming.kicks-ass.net>
Date: Thu, 14 Nov 2024 12:58:31 +0100
From: Peter Zijlstra <peterz@...radead.org>
To: "Gautham R. Shenoy" <gautham.shenoy@....com>
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 Wed, Nov 13, 2024 at 05:11:38PM +0530, Gautham R. Shenoy wrote:

> AMD platforms won't be using FFH based states for offlined CPUs. We
> prefer IO based states when available, and HLT otherwise.
> 
> > 
> > Robustly we'd teach the ACPI driver about FFh and set enter_dead on
> > every state -- but we'd have to double check that with AMD.
> 
> Works for us as long as those FFh states aren't used for play_dead on
> AMD platforms.

AFAIU AMD doesn't want to use MWAIT -- ever, not only for offline.
Confirm?

But if it were to use MWAIT for regular idle, then surely it's OK for
offline too, right?