linux-kernel - Re: [RFC PATCH v4 5/8] x86/smp native_play_dead: Prefer cpuidle_play_dead() over mwait_play

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Message-ID: <CAJZ5v0iA==dmnPbs6BNV_taDD9hRWbwOhiCWsi0BjKzVVdihdg@mail.gmail.com>
Date: Tue, 26 Nov 2024 13:04:51 +0100
From: "Rafael J. Wysocki" <rafael@...nel.org>
To: Patryk Wlazlyn <patryk.wlazlyn@...ux.intel.com>
Cc: "Rafael J. Wysocki" <rafael@...nel.org>, 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, 
	peterz@...radead.org, tglx@...utronix.de, gautham.shenoy@....com
Subject: Re: [RFC PATCH v4 5/8] x86/smp native_play_dead: Prefer
 cpuidle_play_dead() over mwait_play_dead()

On Tue, Nov 26, 2024 at 12:56 PM Patryk Wlazlyn
<patryk.wlazlyn@...ux.intel.com> wrote:
>
> >>> If you first make intel_idle provide :enter_dead() for all CPUs on all
> >>> platforms and implement it by calling mwait_play_dead_with_hint(), you
> >>> won't need mwait_play_dead() any more.
> >> Crossed my mind, but because mwait_play_dead doesn't filter on Intel
> >> vendor specifically,
> >
> > In practice, it does.
> >
> > The vendor check in it is equivalent to "if Intel".
>
> Actually, what about INTEL_IDLE=n?
> We might hit acpi_idle, which would call mwait_play_dead_with_hint() now, but
> if we don't, don't we want to try mwait_play_dead before hlt or is it too
> unrealistic to happen?

In that case the hint to use would not be known anyway, so
hlt_play_dead() is the right choice IMV.