Re: [PATCH v2 1/2] arch_topology: seed capacity_freq_ref with boost-aware max freq

[Vincent Guittot]

On Thu, 17 Sept 2026 at 21:07, Rafael J. Wysocki (Intel)
<rafael@xxxxxxxxxx> wrote:
>
> On Tue, Sep 8, 2026 at 10:31 AM Ananthu C V <ananthu.cv@xxxxxxxxxxxxxxxx> wrote:
> >
> > capacity_freq_ref, the per-CPU frequency-invariance reference used by
> > schedutil, is seeded from policy->cpuinfo.max_freq at policy creation.
> > If boost frequencies are filtered out of the frequency table because
> > boost isn't yet enabled at boot, max_freq only reflects the non-boost
> > ceiling, so capacity_freq_ref never learns about boost frequencies for
> > the policy's lifetime. Enabling boost later raises policy->max, but
> > capacity_freq_ref stays stale, leaving schedutil unable to scale
> > utilization or target a frequency above the non-boost maximum.
> >
> > Track the highest frequency in the table regardless of boost state
> > (max_table_freq) and seed capacity_freq_ref with max(cpuinfo.max_freq,
> > max_table_freq), so the invariance reference is boost-aware from boot
> > regardless of whether boost is currently enabled. Runtime enforcement,
> > still handled by policy->max, is unaffected.
> >
> > Suggested-by: Vincent Guittot <vincent.guittot@xxxxxxxxxx>
> > Signed-off-by: Ananthu C V <ananthu.cv@xxxxxxxxxxxxxxxx>
> > ---
> >  drivers/base/arch_topology.c | 3 ++-
> >  drivers/cpufreq/freq_table.c | 6 ++++++
> >  include/linux/cpufreq.h      | 1 +
> >  3 files changed, 9 insertions(+), 1 deletion(-)
> >
> > diff --git a/drivers/base/arch_topology.c b/drivers/base/arch_topology.c
> > index 8c5e47c28d9a..da94f77441da 100644
> > --- a/drivers/base/arch_topology.c
> > +++ b/drivers/base/arch_topology.c
> > @@ -404,7 +404,8 @@ init_cpu_capacity_callback(struct notifier_block *nb,
> >         cpumask_andnot(cpus_to_visit, cpus_to_visit, policy->related_cpus);
> >
> >         for_each_cpu(cpu, policy->related_cpus) {
> > -               per_cpu(capacity_freq_ref, cpu) = policy->cpuinfo.max_freq;
> > +               per_cpu(capacity_freq_ref, cpu) = max(policy->cpuinfo.max_freq,
> > +                                                     policy->cpuinfo.max_table_freq);
>
> So isn't capacity_freq_ref supposed to correspond to the CPU capacity
> returned by arch_scale_cpu_capacity()?

capacity_freq_ref is the frequency that has been used when computing
the capacity at boot and it should not change at runtime wether the
boost is enabled or not, otherwise you will have some fluctuation on
the system capacity that will create issue with PELT and scheduler

>
> If that's the case and boost was disabled when the CPU capacity was
> computed, how can cpuinfo.max_table_freq correspond to that capacity?
>
> >                 freq_inv_set_max_ratio(cpu,
> >                                        per_cpu(capacity_freq_ref, cpu) * HZ_PER_KHZ);
> >         }
> > diff --git a/drivers/cpufreq/freq_table.c b/drivers/cpufreq/freq_table.c
> > index ea994647abc8..4984142dc08a 100644
> > --- a/drivers/cpufreq/freq_table.c
> > +++ b/drivers/cpufreq/freq_table.c
> > @@ -33,11 +33,15 @@ int cpufreq_frequency_table_cpuinfo(struct cpufreq_policy *policy)
> >         struct cpufreq_frequency_table *pos, *table = policy->freq_table;
> >         unsigned int min_freq = ~0;
> >         unsigned int max_freq = 0;
> > +       unsigned int max_table_freq = 0;
> >         unsigned int freq, i;
> >
> >         cpufreq_for_each_valid_entry_idx(pos, table, i) {
> >                 freq = pos->frequency;
> >
> > +               if (freq > max_table_freq)
> > +                       max_table_freq = freq;
> > +
> >                 if ((!cpufreq_boost_enabled() || !policy->boost_enabled)
> >                     && (pos->flags & CPUFREQ_BOOST_FREQ))
> >                         continue;
> > @@ -57,6 +61,8 @@ int cpufreq_frequency_table_cpuinfo(struct cpufreq_policy *policy)
> >         if (policy->cpuinfo.max_freq < max_freq)
> >                 policy->cpuinfo.max_freq = max_freq;
> >
> > +       policy->cpuinfo.max_table_freq = max_table_freq;
> > +
> >         if (min_freq == ~0)
> >                 return -EINVAL;
> >         else
> > diff --git a/include/linux/cpufreq.h b/include/linux/cpufreq.h
> > index 35ce665edfd8..3f3b1380251a 100644
> > --- a/include/linux/cpufreq.h
> > +++ b/include/linux/cpufreq.h
> > @@ -45,6 +45,7 @@ enum cpufreq_table_sorting {
> >  struct cpufreq_cpuinfo {
> >         unsigned int            max_freq;
> >         unsigned int            min_freq;
> > +       unsigned int            max_table_freq; /* Highest valid frequency in the table */
> >
> >         /* in 10^(-9) s = nanoseconds */
> >         unsigned int            transition_latency;
> >
> > --