linux-kernel - Re: [PATCH v3 3/3] intel_idle: Provide enter

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Message-ID: <CAJZ5v0iR5A8AdEU-v34oG4i9ceW2uS4D2EWfwKcmDVnTO8F9_g@mail.gmail.com>
Date: Tue, 12 Nov 2024 20:43:52 +0100
From: "Rafael J. Wysocki" <rafael@...nel.org>
To: Thomas Gleixner <tglx@...utronix.de>
Cc: "Rafael J. Wysocki" <rafael@...nel.org>, Patryk Wlazlyn <patryk.wlazlyn@...ux.intel.com>, 
	Dave Hansen <dave.hansen@...el.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 3/3] intel_idle: Provide enter_dead() handler for SRF

On Tue, Nov 12, 2024 at 8:18 PM Thomas Gleixner <tglx@...utronix.de> wrote:
>
> On Tue, Nov 12 2024 at 12:28, Rafael J. Wysocki wrote:
> > On Tue, Nov 12, 2024 at 12:18 PM Patryk Wlazlyn
> > <patryk.wlazlyn@...ux.intel.com> wrote:
> >> I don't think so. The old algorithm gives fairly good heuristic for computing
> >> the mwait hint for the deepest cstate. Even though it's not guaranteed to work,
> >> it does work on most of the platforms that don't early return. I think we should
> >> leave it, but prefer idle_driver.
> >
> > IOW, as a fallback mechanism, it is as good as it gets.
> >
> > As the primary source of information though, not quite.
>
> So we have at least 5 places in the kernel which evaluate CPUID leaf 0x5
> in different ways.
>
> Can we please have _ONE_ function which evaluates the leaf correctly
> once and provides the required information for all places ready to use?

Yup, that's what needs to be done.