Re: [PATCH v3 1/2] arch_topology: seed capacity_freq_ref with highest available frequency

[Dietmar Eggemann <dietmar.eggemann@arm.com>]

On 11.10.26 16:16, Zhongqiu Han wrote:
> On 9/29/2026 7:38 PM, Ananthu C V wrote:

[...]

> Besides, could you comment patch v2 Dietmar's comments? It seems that
> patch 1/2 exposes a pre-existing ordering issue. On DT systems,
> cpu_scale is normalized only from the CPUFREQ_CREATE_POLICY notification
> of the last policy, so the cpufreq pressure of every other policy is
> computed in cpufreq_init_policy() from the raw, not yet normalized,
> capacity, and stays cached until the next cpufreq_set_policy() for that
> policy. So far this was harmless because capacity_freq_ref == policy-
>>max at boot, so the pressure was 0 regardless of the capacity. With
> 1/2, capacity_freq_ref covers the boost frequencies while boost is
> disabled at boot, so policy->max < capacity_freq_ref becomes the common
> case and the stale value becomes visible (102 vs 79 on Juno R0, as
> reported by Dietmar). Perhaps the limits of all policies could be
> refreshed once from parsing_done_workfn(), after the capacities have
> been normalized?
> 
> --- a/drivers/base/arch_topology.c
> +++ b/drivers/base/arch_topology.c
> @@ -454,9 +454,27 @@ core_initcall(register_cpufreq_notifier);
> 
>  static void parsing_done_workfn(struct work_struct *work)
>  {
> +    int cpu;
> +
>      cpufreq_unregister_notifier(&init_cpu_capacity_notifier,
>                       CPUFREQ_POLICY_NOTIFIER);
>      free_cpumask_var(cpus_to_visit);
> +
> +    /*
> +     * The cpufreq pressure of all policies but the last one has been
> +     * computed before topology_normalize_cpu_scale(), so refresh it now
> +     * that cpu_scale is final.
> +     */
> +    for_each_possible_cpu(cpu) {
> +        struct cpufreq_policy *policy __free(put_cpufreq_policy) =
> +            cpufreq_cpu_get(cpu);
> +
> +        if (!policy || cpu != policy->cpu)
> +            continue;
> +
> +        guard(cpufreq_policy_write)(policy);
> +        refresh_frequency_limits(policy);
> +    }
Yes, IMHO, something like this is needed.

[    1.169158] cpufreq_notifier_max(): current=[kworker/u26:0 46] policy->related_cpus=[]												(1)
[    1.169209] init_cpu_capacity_callback(): current=[kworker/u26:0 46] policy->related_cpus=[0,3-5]
[    1.169992] cpufreq_update_pressure(): current=[kworker/u26:0 46] policy->related_cpus=[0,3-5] policy->max=700000 pressure=102 max_capacity=578 capped_freq=700000 max_freq=850000
[    1.170203] cpufreq_update_pressure(): current=[kworker/2:2 67] policy->related_cpus=[0,3-5] policy->max=700000 pressure=102 max_capacity=578 capped_freq=700000 max_freq=850000 	(2)
[    1.170835] cpufreq_notifier_max(): current=[kworker/u26:0 46] policy->related_cpus=[]												(1)
[    1.170872] init_cpu_capacity_callback(): current=[kworker/u26:0 46] policy->related_cpus=[1-2]
[    1.174516] cpufreq_update_pressure(): current=[kworker/u26:0 46] policy->related_cpus=[1-2] policy->max=800000 pressure=280 max_capacity=1024 capped_freq=800000 max_freq=1100000
[    1.175261] cpufreq_update_pressure(): current=[kworker/2:2 67] policy->related_cpus=[1-2] policy->max=800000 pressure=280 max_capacity=1024 capped_freq=800000 max_freq=1100000	(2)
[    1.187698] cpufreq_update_pressure(): current=[kworker/2:0 28] policy->related_cpus=[0,3-5] policy->max=700000 pressure=79 max_capacity=446 capped_freq=700000 max_freq=850000	(3)
[    1.187847] cpufreq_update_pressure(): current=[kworker/2:0 28] policy->related_cpus=[1-2] policy->max=800000 pressure=280 max_capacity=1024 capped_freq=800000 max_freq=1100000	(3)

The work scheduled in (1) also still operates on raw capacity (2).

(3) shows your extension in parsing_done_workfn() work function which
    gets scheduled when all CPUs are initialised, so
    topology_normalize_cpu_scale() had been called.

Not sure whether we can call cpufreq_update_limits(cpu) there instead
(maybe extended with a 'only do this for policy->cpu'?). So we won't
have to expose cpufreq internals in /drivers/base/arch_topology.c.