Re: [PATCH] cpufreq: Use a non-boost reference frequency for pressure calculation

[Mario Limonciello]

On 9/17/26 12:38, Rafael J. Wysocki (Intel) wrote:
> On Tue, Sep 15, 2026 at 9:03 AM Jianyong Wu <wujianyong@xxxxxxxx> wrote:
> > Commit d2d5c129d07e ("cpufreq: Make cpufreq_update_pressure() fall
> > back to cpuinfo.max_freq") introduced cpuinfo.max_freq as the reference
> > frequency for cpufreq pressure when arch_scale_freq_ref() returns zero.
> >
> > However, cpuinfo.max_freq may include boost frequencies and therefore
> > does not necessarily represent the maximum sustainable frequency.
>
> And then it really matters what is sustainable and for how long.
>
> > On some systems using acpi-cpufreq, cpuinfo.max_freq includes boost while
> > the frequency table only contains non-boost frequencies.
>
> In which case selecting freq_table[0] may give the processor a license
> to go to the turbo (or boost) frequency range.
>
> > Consequently, cpufreq pressure remains nonzero even without an additional
> > frequency limit.
>
> So when and where does this matter?
>
> > Furthermore, drivers may update cpuinfo.max_freq when boost is enabled
> > or disabled. With a fixed policy limit below the maximum non-boost
> > frequency, this changes the pressure reference and hence the reported
> > pressure, although the non-boost frequency limit remains unchanged.
>
> If the capacity is updated though along with the cpuinfo.max_freq
> change, then this is all fine because the pressure is then computed
> relative to the new capacity.  intel_pstate does that.
>
> > Add max_sustainable_freq to struct cpufreq_cpuinfo to provide a reference
> > frequency excluding boost. Populate it from the nominal frequency in
> > amd-pstate and cppc_cpufreq, the maximum non-turbo frequency in
> > intel_pstate, and the highest frequency-table entry in acpi-cpufreq.
> >
> > Use this value when arch_scale_freq_ref() returns zero. Preserve the
> > existing cpuinfo.max_freq fallback for drivers that leave the new field
> > at zero.
> >
> > Tested with acpi-cpufreq, intel_pstate, and amd-pstate in active and
> > passive modes. With no additional frequency limit, pressure is zero.
> > With a fixed limit below the non-boost reference frequency, pressure
> > remains unchanged across boost transitions.
>
> Which may not be what is intended.
>
> > Fixes: d2d5c129d07e ("cpufreq: Make cpufreq_update_pressure() fall back to cpuinfo.max_freq")
> > Signed-off-by: Jianyong Wu <wujianyong@xxxxxxxx>
> > ---
> > The earlier fix was incorrect and has been abandoned. This patch takes
> > a different approach.
> >
> > Previous discussion: https://lore.kernel.org/all/SI2PR04MB4931A8BA0EF213B0238BD9E4E3BD2@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx/
> >
> >   drivers/cpufreq/acpi-cpufreq.c | 3 +++
> >   drivers/cpufreq/amd-pstate.c   | 2 ++
> >   drivers/cpufreq/cppc_cpufreq.c | 3 ++-
> >   drivers/cpufreq/cpufreq.c      | 4 +++-
> >   drivers/cpufreq/intel_pstate.c | 2 ++
> >   include/linux/cpufreq.h        | 2 ++
> >   6 files changed, 14 insertions(+), 2 deletions(-)
> >
> > diff --git a/drivers/cpufreq/acpi-cpufreq.c b/drivers/cpufreq/acpi-cpufreq.c
> > index 21639d9ac753..e7b22456ebb8 100644
> > --- a/drivers/cpufreq/acpi-cpufreq.c
> > +++ b/drivers/cpufreq/acpi-cpufreq.c
> > @@ -856,6 +856,9 @@ static int acpi_cpufreq_cpu_init(struct cpufreq_policy *policy)
> >          }
> >          freq_table[valid_states].frequency = CPUFREQ_TABLE_END;
> >
> > +       /* Init max sustainable cpu frequency */
> > +       policy->cpuinfo.max_sustainable_freq = freq_table[0].frequency;
> > +

Maybe I'm missing something, but it sounds to me like it would make 
sense to just:

policy->cpuinfo.nominal_freq = freq_table[0].frequency

and then use cpuinfo.nominal_freq everywhere, no?

> >          max_boost_ratio = get_max_boost_ratio(cpu, &nominal_freq);
> >          if (max_boost_ratio) {
> >                  unsigned int freq = nominal_freq;
> > diff --git a/drivers/cpufreq/amd-pstate.c b/drivers/cpufreq/amd-pstate.c
> > index 3a6b4b224a66..6fc28bb1499b 100644
> > --- a/drivers/cpufreq/amd-pstate.c
> > +++ b/drivers/cpufreq/amd-pstate.c
> > @@ -1085,6 +1085,7 @@ static int amd_pstate_cpu_init(struct cpufreq_policy *policy)
> >                                                  perf.lowest_perf);
> >          policy->cpuinfo.max_freq = cpudata->max_freq;
> >
> > +       policy->cpuinfo.max_sustainable_freq = cpudata->nominal_freq;
> >          policy->driver_data = cpudata;
> >          ret = amd_pstate_cppc_enable(policy);
> >          if (ret)
> > @@ -1912,6 +1913,7 @@ static int amd_pstate_epp_cpu_init(struct cpufreq_policy *policy)
> >          policy->cpuinfo.min_freq = perf_to_freq(perf, cpudata->nominal_freq,
> >                                                  perf.lowest_perf);
> >          policy->cpuinfo.max_freq = cpudata->max_freq;
> > +       policy->cpuinfo.max_sustainable_freq = cpudata->nominal_freq;
> >          policy->driver_data = cpudata;
> >
> >          ret = amd_pstate_cppc_enable(policy);
> > diff --git a/drivers/cpufreq/cppc_cpufreq.c b/drivers/cpufreq/cppc_cpufreq.c
> > index 6fe0e972952a..f803fcdca483 100644
> > --- a/drivers/cpufreq/cppc_cpufreq.c
> > +++ b/drivers/cpufreq/cppc_cpufreq.c
> > @@ -682,7 +682,8 @@ static int cppc_cpufreq_cpu_init(struct cpufreq_policy *policy)
> >          policy->cpuinfo.min_freq = cppc_perf_to_khz(caps, caps->lowest_perf);
> >          policy->cpuinfo.max_freq = cppc_perf_to_khz(caps, policy->boost_enabled ?
> >                                                      caps->highest_perf : caps->nominal_perf);
> > -
> > +       policy->cpuinfo.max_sustainable_freq =
> > +               cppc_perf_to_khz(caps, caps->nominal_perf);
> >          policy->transition_delay_us = cppc_cpufreq_get_transition_delay_us(cpu);
> >          policy->shared_type = cpu_data->shared_type;
> >
> > diff --git a/drivers/cpufreq/cpufreq.c b/drivers/cpufreq/cpufreq.c
> > index b898b6544069..c1d54a22265d 100644
> > --- a/drivers/cpufreq/cpufreq.c
> > +++ b/drivers/cpufreq/cpufreq.c
> > @@ -2587,7 +2587,9 @@ static void cpufreq_update_pressure(struct cpufreq_policy *policy)
> >          cpu = cpumask_first(policy->related_cpus);
> >          max_freq = arch_scale_freq_ref(cpu);
> >          if (!max_freq)
> > -               max_freq = policy->cpuinfo.max_freq;
> > +               max_freq = policy->cpuinfo.max_sustainable_freq ?
> > +                                policy->cpuinfo.max_sustainable_freq :
> > +                                policy->cpuinfo.max_freq;
> >
> >          capped_freq = policy->max;
> >
> > diff --git a/drivers/cpufreq/intel_pstate.c b/drivers/cpufreq/intel_pstate.c
> > index 6e984c114d96..daef7e99fead 100644
> > --- a/drivers/cpufreq/intel_pstate.c
> > +++ b/drivers/cpufreq/intel_pstate.c
> > @@ -1474,6 +1474,7 @@ static void __intel_pstate_update_max_freq(struct cpufreq_policy *policy,
> >
> >          policy->cpuinfo.max_freq = READ_ONCE(global.no_turbo) ?
> >                          cpudata->pstate.max_freq : cpudata->pstate.turbo_freq;
> > +       policy->cpuinfo.max_sustainable_freq = cpudata->pstate.max_freq;
> >
> >          refresh_frequency_limits(policy);
> >   }
> > @@ -3052,6 +3053,7 @@ static int __intel_pstate_cpu_init(struct cpufreq_policy *policy)
> >          policy->cpuinfo.min_freq = cpu->pstate.min_freq;
> >          policy->cpuinfo.max_freq = READ_ONCE(global.no_turbo) ?
> >                          cpu->pstate.max_freq : cpu->pstate.turbo_freq;
> > +       policy->cpuinfo.max_sustainable_freq = cpu->pstate.max_freq;
> >
> >          intel_pstate_init_acpi_perf_limits(policy);
> >
> > diff --git a/include/linux/cpufreq.h b/include/linux/cpufreq.h
> > index ae9d1ce4f49c..aa3f60a167be 100644
> > --- a/include/linux/cpufreq.h
> > +++ b/include/linux/cpufreq.h
> > @@ -45,6 +45,8 @@ enum cpufreq_table_sorting {
> >   struct cpufreq_cpuinfo {
> >          unsigned int            max_freq;
> >          unsigned int            min_freq;
> > +       /* Maximum sustainable frequency excluding boost, or 0 if unknown. */
> > +       unsigned int            max_sustainable_freq;
> >
> >          /* in 10^(-9) s = nanoseconds */
> >          unsigned int            transition_latency;
> > --
> > 2.34.1