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

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Message-ID: <3e1807d3-82cd-7ade-d361-e1982a4848a9@arm.com>
Date:   Thu, 28 Oct 2021 08:19:05 +0100
From:   Lukasz Luba <lukasz.luba@....com>
To:     Viresh Kumar <viresh.kumar@...aro.org>
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 10/28/21 6:44 AM, Viresh Kumar wrote:
> 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 ?

Sure

> 
>> + *
>> + * 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 :)

OK :)

> 
>> +		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.

OK, I'll change that.

Thank you for the review.

Regards,
Lukasz