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

[Mario Limonciello <mario.limonciello@amd.com>]

On 9/17/26 12:38, Rafael J. Wysocki (Intel) wrote:
> On Tue, Sep 15, 2026 at 9:03 AM Jianyong Wu <wujianyong@hygon.cn> 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@hygon.cn>
>> ---
>> The earlier fix was incorrect and has been abandoned. This patch takes
>> a different approach.
>>
>> Previous discussion: https://lore.kernel.org/all/SI2PR04MB4931A8BA0EF213B0238BD9E4E3BD2@SI2PR04MB4931.apcprd04.prod.outlook.com/
>>
>>   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
>>
>>