Re: [PATCH] sched/fair: Only apply cpufreq pressure where frequency is invariant

[K Prateek Nayak]

On 9/7/2026 1:37 PM, K Prateek Nayak wrote:
> So, I've been trying to understand these bits and looking at
> cpufreq_policy_init_qos(), the "policy->cpuinfo.max_freq" should be the
> frequency including the boost range but I see cpufreq_update_pressure()
> and it says:
> 
>     max_freq = arch_scale_freq_ref(cpu);
>     if (!max_freq)
>         max_freq = policy->cpuinfo.max_freq;
> 
>     capped_freq = policy->max;
> 
>     /*
>      * Handle properly the boost frequencies, which should simply clean
>      * the cpufreq pressure value.
>      */
>     if (max_freq <= capped_freq) {
>         ...
>     }
> 
> 
> Looking at this, I feel "policy->cpuinfo.max_freq" should not include
> the boost frequency, or x86 should implement a arch_scale_freq_ref()
> to know when boost is enabled vs disabled.
> 
> If cpufreq_update_pressure() indeed has to disregard boost frequency,
> and anything above P0 is not considered as pressure, we can simply
> do:
> 
> diff --git a/drivers/cpufreq/cpufreq.c b/drivers/cpufreq/cpufreq.c
> index b898b6544069..068e6d6e15a1 100644
> --- a/drivers/cpufreq/cpufreq.c
> +++ b/drivers/cpufreq/cpufreq.c
> @@ -2586,8 +2586,11 @@ 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;
> +	if (!max_freq) {
> +		max_freq = __resolve_freq(policy, policy->cpuinfo.max_freq,
> +					  policy->max, policy->min,

My bad, that should have been other way around and use the cpuinfo
fields to prevent capping based on policy limits. Updated diff:

diff --git a/drivers/cpufreq/cpufreq.c b/drivers/cpufreq/cpufreq.c
index b898b6544069..97f4a3ba5107 100644
--- a/drivers/cpufreq/cpufreq.c
+++ b/drivers/cpufreq/cpufreq.c
@@ -2586,8 +2586,11 @@ 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;
+	if (!max_freq) {
+		max_freq = __resolve_freq(policy, policy->cpuinfo.max_freq,
+					  policy->cpuinfo.min_freq, policy->cpuinfo.max_freq,
+					  CPUFREQ_RELATION_H);
+	}
 
 	capped_freq = policy->max;
 
---

> +					  CPUFREQ_RELATION_H);
> +	}
>  
>  	capped_freq = policy->max;
>  
> ---
> 
> __resolve_freq() will cap "policy->cpuinfo.max_freq" based on the freq_table
> entries if it exists (acpi-cpufreq), or otherwise return
> "policy->cpuinfo.max_freq" as is for drivers that uses CPPC based scaling
> (amd-pstate, intel_pstate).
> 
> Thoughts? 
> 

-- 
Thanks and Regards,
Prateek