Re: [PATCH] cpufreq: intel_pstate: Fix Raptor Lake-E cpufreq limits

[Rafael J. Wysocki]

On Tue, May 12, 2026 at 1:15 PM srinivas pandruvada
<srinivas.pandruvada@xxxxxxxxxxxxxxx> wrote:
>
> On Tue, 2026-05-12 at 12:20 +0200, Rafael J. Wysocki wrote:
> > On Tue, May 12, 2026 at 1:53 AM Srinivas Pandruvada
> > <srinivas.pandruvada@xxxxxxxxxxxxxxx> wrote:
> > >
> > > Raptor Lake-E processors are not correctly showing cpufreq
> > > frequency
> > > limits.
> > >
> > > These CPUs don't set X86_FEATURE_HYBRID_CPU and have no E-cores,
> > > but
> > > P-cores still use hybrid scaling factor.
> > >
> > > commit 0fcfc9e51990 ("cpufreq: intel_pstate: Fix scaling for
> > > hybrid-capable systems with disabled E-cores") added support for
> > > such configuration. Here using CPPC nominal freq and perf was
> > > compared
> > > to still return hybrid scaling factor.
> > >
> > > Commit 9b18d536b124 ("cpufreq: intel_pstate: Use CPPC to get
> > > scaling
> > > factors") restructured hwp_get_cpu_scaling() and added an explicit
> > > check
> > > for X86_FEATURE_HYBRID_CPU and when not set returns core scaling
> > > factor.
> > >
> > > To address this remove check for X86_FEATURE_HYBRID_CPU and call
> > > intel_pstate_cppc_get_scaling().
> > >
> > > Ideally this change should be enough. But using CPPC for scaling
> > > factor
> > > results in rounding error, so still doesn't restore the original
> > > behavior.
> > >
> > > In intel_pstate_cppc_get_scaling() return core scaling factor when
> > > ACPI CPPC is not present or when CPPC nominal frequency or nominal
> > > performance are invalid.
> > >
> > > Use hybrid_scaling_factor for P-cores when defined for a CPU, if
> > > not
> > > calculate from ACPI CPPC nominal frequency and performance.
> > >
> > > Fixes: 9b18d536b124 ("cpufreq: intel_pstate: Use CPPC to get
> > > scaling factors")
> > > Reported-by: Henry Tseng <henrytseng@xxxxxxxx>
> > > Closes:
> > > https://lore.kernel.org/linux-pm/20260508063032.3248602-1-henrytseng@xxxxxxxx/
> > > Signed-off-by: Srinivas Pandruvada
> > > <srinivas.pandruvada@xxxxxxxxxxxxxxx>
> > > Cc: stable@xxxxxxxxxxxxxxx
> > > ---
> > >  drivers/cpufreq/intel_pstate.c | 29 +++++++++++++++--------------
> > >  1 file changed, 15 insertions(+), 14 deletions(-)
> > >
> > > diff --git a/drivers/cpufreq/intel_pstate.c
> > > b/drivers/cpufreq/intel_pstate.c
> > > index 1292da53e5fc..0379efdee5f8 100644
> > > --- a/drivers/cpufreq/intel_pstate.c
> > > +++ b/drivers/cpufreq/intel_pstate.c
> > > @@ -421,15 +421,23 @@ static int intel_pstate_cppc_get_scaling(int
> > > cpu)
> > >  {
> > >         struct cppc_perf_caps cppc_perf;
> > >
> > > +       if (cppc_get_perf_caps(cpu, &cppc_perf) ||
> > > !cppc_perf.nominal_freq ||
> > > +           !cppc_perf.nominal_perf)
> > > +               goto core_scaling;
> > > +
> > > +       if (cppc_perf.nominal_perf * 100 == cppc_perf.nominal_freq)
> > > +               goto core_scaling;
> > > +
> > > +       if (hybrid_scaling_factor)
> > > +               return hybrid_scaling_factor;
> > > +
> > >         /*
> > > -        * Compute the perf-to-frequency scaling factor for the
> > > given CPU if
> > > -        * possible, unless it would be 0.
> > > +        * Compute the perf-to-frequency scaling factor for the
> > > given CPU
> > > +        * from nominal freq and nominal_perf
> > >          */
> > > -       if (!cppc_get_perf_caps(cpu, &cppc_perf) &&
> > > -           cppc_perf.nominal_perf && cppc_perf.nominal_freq)
> > > -               return div_u64(cppc_perf.nominal_freq *
> > > KHZ_PER_MHZ,
> > > -                              cppc_perf.nominal_perf);
> > > +       return div_u64(cppc_perf.nominal_freq * KHZ_PER_MHZ,
> > > cppc_perf.nominal_perf);
> > >
> > > +core_scaling:
> > >         return core_get_scaling();
> > >  }
> > >
> > > @@ -2281,17 +2289,10 @@ static int hwp_get_cpu_scaling(int cpu)
> > >                  */
> > >                 if (hybrid_get_cpu_type(cpu) ==
> > > INTEL_CPU_TYPE_CORE)
> > >                         return hybrid_scaling_factor;
> > > -
> > > -               return core_get_scaling();
> >
> > Why is this change necessary or even useful?
> >
> > This is about E-cores (because P-cores have been covered above) and
> > if
> > hybrid_scaling_factor is set, it is known that the processor is
> > hybrid
> > and E-cores have the "core" scaling factor.
> >
> > Or is Raptor Lake-E covered by one of the
> > intel_hybrid_scaling_factor[] entries and hybrid_get_cpu_type(cpu)
> > doesn't return INTEL_CPU_TYPE_CORE on it?  This piece of information
> > is missing from the changelog.
>
> Raptor Lake-E (Xeon) uses CPU model as Raptor Lake-S, for which there
> is already a hardcoded scaling factor in the driver.

This piece of information needs to be added to the changelog in the
first place because it is key here.

> So this "if" block will enter. But since there is no hybrid CPUID feature is defined,
> hybrid_get_cpu_type(cpu) will return 0 for P-core or E-core. Here there
> are no E-cores. So need to remove core_get_scaling() as this will
> return non hybrid factor.

Well, what about this:

---
 drivers/cpufreq/intel_pstate.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

--- a/drivers/cpufreq/intel_pstate.c
+++ b/drivers/cpufreq/intel_pstate.c
@@ -2279,7 +2279,7 @@ static int hwp_get_cpu_scaling(int cpu)
          * Return the hybrid scaling factor for P-cores and use the
          * default core scaling for E-cores.
          */
-        if (hybrid_get_cpu_type(cpu) == INTEL_CPU_TYPE_CORE)
+        if (hybrid_get_cpu_type(cpu) != INTEL_CPU_TYPE_ATOM)
             return hybrid_scaling_factor;

         return core_get_scaling();

Or is the original Raptor Lake-S scaling factor unsuitable for Raptor Lake-E?

>
>
> >
> > >         }
> > >
> > > -       /* Use core scaling on non-hybrid systems. */
> > > -       if (!cpu_feature_enabled(X86_FEATURE_HYBRID_CPU))
> > > -               return core_get_scaling();
> > > -
> >
> > So we're now exposing all of the non-hybrid processors to the fun
> > with
> > possibly incorrectly populated CPPC, which is kind of risky.
> >
>
> This was already used before with
> commit0fcfc9e51990246a9813475716746ff5eb98c6aa
> relying that all non hybrid processor (including servers) didn't set
> nominal frequency, so will return core_scaling without using CPPC.
> I retested change on servers and non hybrids.
>
> > If Raptor Lake-E is not covered by an existing
> > intel_hybrid_scaling_factor[] entry, why don't we add one for it with
> > a "scaling factor" value indicating that CPPC needs to be used for
> > computing it on all CPUs?
>
> It is already covered by existing, but we can only call
> for intel_pstate_cppc_get_scaling() when hybrid_scaling_factor is
> defined. This will require a hardcoding for Bartlett Lake also which
> uses different CPU model, which Henry Tseng is planing to send.

I would add a new intel_hybrid_scaling_factor[] entry for Bartlett
Lake then with a proper scaling factor along with the change above.