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

[Rafael J. Wysocki (Intel)]

On Fri, Sep 18, 2026 at 8:24 AM Vincent Guittot
<vincent.guittot@xxxxxxxxxx> wrote:
>
> 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

I get it, and so it is what I wrote above: The frequency of the CPU
when running at the arch_scale_cpu_capacity() performance level.
Isn't it?

> 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

So the capacity should be constant and consequently, capacity_freq_ref
should be constant.

Also, if boost is not enabled when capacity_freq_ref is set and there
are frequency levels marked as "boost" in the table, it cannot be the
maximum frequency in the table because that's not what is used for
computing the capacity.