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From:   "Rafael J. Wysocki" <rafael@kernel.org>
Date:   Tue, 25 Oct 2022 15:03:49 +0200
Message-ID: <CAJZ5v0gMhzWiBm5H8V6eHfsCyJ0tyEaCfYJo0TvCeug6_Ek+DA@mail.gmail.com>
Subject: Re: [PATCH 0/2] cpufreq: intel_pstate: Make HWP calibration work on
 all hybrid platforms
To:     srinivas pandruvada <srinivas.pandruvada@linux.intel.com>
Cc:     "Rafael J. Wysocki" <rjw@rjwysocki.net>,
        Linux PM <linux-pm@vger.kernel.org>,
        LKML <linux-kernel@vger.kernel.org>,
        Len Brown <len.brown@intel.com>,
        Linux ACPI <linux-acpi@vger.kernel.org>
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On Tue, Oct 25, 2022 at 1:58 AM srinivas pandruvada
<srinivas.pandruvada@linux.intel.com> wrote:
>
> 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@linux.intel.com>
> Tested-by: Srinivas Pandruvada <srinivas.pandruvada@linux.intel.com>

Thank you!

As discussed offline, I'm going to fast-track this series as urgent
fixes to cover systems in the field that are likely to have problems
related to it.