Re: [PATCH v2] cpufreq: cppc: Clamp default minimum limit to lowest_nonlinear_perf

[Jie Zhan]

On 2/13/2026 6:06 PM, Pengjie Zhang wrote:
> The ACPI spec defines 'lowest_nonlinear_perf' as the threshold for
> linear performance scaling. Performance levels below this threshold
> are typically inefficient and should not be used by default.
> 
> Currently, the QoS minimum request is initialized to 0. This defaults
I'm more curious on the original commit that overrides the policy->min set
by driver, which is:
521223d8b3ec ("cpufreq: Fix initialization of min and max frequency QoS requests")

The changelog says:
"The min and max frequency QoS requests in the cpufreq core are initialized
to whatever the current min and max frequency values are at the init time,
but if any of these values change later (for example, cpuinfo.max_freq is
updated by the driver), these initial request values will be limiting the
CPU frequency unnecessarily unless they are changed by user space via
sysfs."

So, instead of doing what the patch did, what about calling
freq_qos_update_request(policy->max_freq_req, xxx) when cpuinfo.max_freq is
updated?

Jie

> the performance floor to the absolute "Lowest Performance" state
> instead of "lowest_nonlinear_perf", allowing the CPU to operate in
> an inefficient range unnecessarily.
> 
> Signed-off-by: Pengjie Zhang <zhangpengjie2@xxxxxxxxxx>
> ---
> Changes in v2:
>   - Renamed the patch subject to better reflect the logic change.
>   - Updated the commit log to clarify ACPI spec details.
> Link to v1:https://lore.kernel.org/all/20260116094555.2978887-1-zhangpengjie2@xxxxxxxxxx/
> ---
>  drivers/cpufreq/cppc_cpufreq.c | 18 ++++++++++++++++--
>  1 file changed, 16 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/cpufreq/cppc_cpufreq.c b/drivers/cpufreq/cppc_cpufreq.c
> index 7e8042efedd1..4a3031d9fcf4 100644
> --- a/drivers/cpufreq/cppc_cpufreq.c
> +++ b/drivers/cpufreq/cppc_cpufreq.c
> @@ -333,9 +333,23 @@ static unsigned int cppc_cpufreq_fast_switch(struct cpufreq_policy *policy,
>  	return target_freq;
>  }
>  
> -static int cppc_verify_policy(struct cpufreq_policy_data *policy)
> +static int cppc_verify_policy(struct cpufreq_policy_data *policy_data)
>  {
> -	cpufreq_verify_within_cpu_limits(policy);
> +	if (policy_data->min == FREQ_QOS_MIN_DEFAULT_VALUE) {
> +		struct cpufreq_policy *policy __free(put_cpufreq_policy) =
> +					      cpufreq_cpu_get(policy_data->cpu);
> +		struct cppc_cpudata *cpu_data;
> +
> +		if (!policy)
> +			return -EINVAL;
> +
> +		cpu_data = policy->driver_data;
> +		policy_data->min = cppc_perf_to_khz(&cpu_data->perf_caps,
> +			cpu_data->perf_caps.lowest_nonlinear_perf);
> +	}
> +
> +	cpufreq_verify_within_cpu_limits(policy_data);
> +
>  	return 0;
>  }
>