linux-kernel - Re: [PATCH 0/2] cpufreq: intel_pstate: Make HWP calibration work on all hybrid platforms

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Date:   Mon, 24 Oct 2022 15:14:36 -0700
From:   srinivas pandruvada <srinivas.pandruvada@...ux.intel.com>
To:     "Rafael J. Wysocki" <rjw@...ysocki.net>,
        Linux PM <linux-pm@...r.kernel.org>
Cc:     LKML <linux-kernel@...r.kernel.org>,
        Len Brown <len.brown@...el.com>,
        Linux ACPI <linux-acpi@...r.kernel.org>
Subject: Re: [PATCH 0/2] cpufreq: intel_pstate: Make HWP calibration work on
 all hybrid platforms

On Mon, 2022-10-24 at 21:18 +0200, Rafael J. Wysocki wrote:
> Hi All,
> 
> The HWP calibration in intel_pstate is needed to map HWP performance
> levels to
> frequencies, which are used in the cpufreq sysfs interface, in a
> reliable way.
> On all non-hybrid "core" platforms it is sufficient to multiply the
> HWP
> performance levels by 100000 to obtain the corresponding frequencies,
> but on
> hybrid ones there is a difference between P-cores and E-cores.
> 
> Previous attempts to make this work were based on using CPPC (and in
> particular
> the nominal performance values provided by _CPC), but it turns out
> that the
> CPPC information is not sufficiently reliable for this purpose and
> the only
> way to do it is to use a hard-coded scaling factors for P-cores and
> for E-cores
> (which fortunately is the same as in the non-hybrid case). 
> Fortunately, the
> same scaling factor for P-cores works on all of the hybrid platforms
> to date.
> 
> The first patch in the series ensures that all of the CPUs will use
> correct
> information from MSRs by avoiding the situations in which an MSR
> values read
> on one CPU will be used for performance scaling of another CPU.
> 
> The second one implements the approach outlined above.
> 
> Please see the changelogs for details.

Acked-by: Srinivas Pandruvada <srinivas.pandruvada@...ux.intel.com>
Tested-by: Srinivas Pandruvada <srinivas.pandruvada@...ux.intel.com>


> 
> Thanks!
> 
> 
>