linux-kernel - Re: [PATCH v2 1/5] arch_topology: Introduce thermal pressure update function

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Date:   Thu, 28 Oct 2021 11:14:59 +0530
From:   Viresh Kumar <viresh.kumar@...aro.org>
To:     Lukasz Luba <lukasz.luba@....com>
Cc:     linux-kernel@...r.kernel.org, linux-pm@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org,
        linux-arm-msm@...r.kernel.org, sudeep.holla@....com,
        will@...nel.org, catalin.marinas@....com, linux@...linux.org.uk,
        gregkh@...uxfoundation.org, rafael@...nel.org, amitk@...nel.org,
        daniel.lezcano@...aro.org, amit.kachhap@...il.com,
        thara.gopinath@...aro.org, bjorn.andersson@...aro.org,
        agross@...nel.org
Subject: Re: [PATCH v2 1/5] arch_topology: Introduce thermal pressure update
 function

On 15-10-21, 15:45, Lukasz Luba wrote:
> +/**
> + * topology_thermal_pressure_update() - Update thermal pressure for CPUs
> + * @cpus	: The related CPUs for which capacity has been reduced
> + * @capped_freq	: The maximum allowed frequency that CPUs can run at

Maybe replace tabs with spaces here ?

> + *
> + * Update the value of thermal pressure for all @cpus in the mask. The
> + * cpumask should include all (online+offline) affected CPUs, to avoid
> + * operating on stale data when hot-plug is used for some CPUs. The
> + * @capped_freq must be less or equal to the max possible frequency and
> + * reflects the currently allowed max CPUs frequency due to thermal capping.
> + * The @capped_freq must be provided in kHz.
> + */
> +void topology_thermal_pressure_update(const struct cpumask *cpus,
> +				      unsigned long capped_freq)
> +{
> +	unsigned long max_capacity, capacity;
> +	int cpu;
> +
> +	if (!cpus)

I will drop this and let the kernel crash :)

> +		return;
> +
> +	cpu = cpumask_first(cpus);
> +	max_capacity = arch_scale_cpu_capacity(cpu);
> +
> +	/* Convert to MHz scale which is used in 'freq_factor' */
> +	capped_freq /= 1000;

We should make sure capped_freq > freq_factor and WARN if not. This will also
get rid of similar checks at the users.

> +
> +	capacity = mult_frac(capped_freq, max_capacity,
> +			     per_cpu(freq_factor, cpu));
> +
> +	arch_set_thermal_pressure(cpus, max_capacity - capacity);
> +}
> +EXPORT_SYMBOL_GPL(topology_thermal_pressure_update);

-- 
viresh