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

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Message-ID: <87serwmfbx.ffs@tglx>
Date: Tue, 12 Nov 2024 20:17:54 +0100
From: Thomas Gleixner <tglx@...utronix.de>
To: "Rafael J. Wysocki" <rafael@...nel.org>, Patryk Wlazlyn
 <patryk.wlazlyn@...ux.intel.com>, Dave Hansen <dave.hansen@...el.com>
Cc: 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 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?

Thanks,

        tglx