linux-kernel - Re: [PATCH V2 1/3] Calculate Thermal Pressure

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Date:   Wed, 24 Apr 2019 18:38:02 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Thara Gopinath <thara.gopinath@...aro.org>
Cc:     mingo@...hat.com, rui.zhang@...el.com,
        linux-kernel@...r.kernel.org, amit.kachhap@...il.com,
        viresh.kumar@...aro.org, javi.merino@...nel.org,
        edubezval@...il.com, daniel.lezcano@...aro.org,
        vincent.guittot@...aro.org, nicolas.dechesne@...aro.org,
        bjorn.andersson@...aro.org, dietmar.eggemann@....com
Subject: Re: [PATCH V2 1/3] Calculate Thermal Pressure

On Tue, Apr 16, 2019 at 03:38:39PM -0400, Thara Gopinath wrote:

> +static void thermal_pressure_update(struct thermal_pressure *cpu_thermal,
> +				    unsigned long cap_max_freq,
> +				    unsigned long max_freq, bool change_scale)
> +{
> +	unsigned long flags = 0;
> +
> +	calculate_thermal_pressure(cpu_thermal);
> +	if (change_scale)
> +		cpu_thermal->raw_scale =
> +			(cap_max_freq << SCHED_CAPACITY_SHIFT) / max_freq;

That needs {} per coding style.

> +
> +	mod_timer(&cpu_thermal->timer, jiffies +
> +				usecs_to_jiffies(TICK_USEC));
> +
> +	spin_unlock_irqrestore(&cpu_thermal->lock, flags);

This is busted has heck, @flags should be the result of irqsave(.flags).

> +}
> +
> +/**
> + * Function for the tick update of the thermal pressure.
> + * The thermal pressure update is aborted if already an update is
> + * happening.
> + */
> +static void thermal_pressure_timeout(struct timer_list *timer)
> +{
> +	struct thermal_pressure *cpu_thermal = from_timer(cpu_thermal, timer,
> +							  timer);

If you split after the = the result is so very much easier to read.

> +	unsigned long flags = 0;
> +
> +	if (!cpu_thermal)
> +		return;
> +
> +	if (!spin_trylock_irqsave(&cpu_thermal->lock, flags))
> +		return;
> +
> +	thermal_pressure_update(cpu_thermal, 0, 0, 0);
> +}
> +
> +/**
> + * Function to update thermal pressure from cooling device
> + * or any framework responsible for capping cpu maximum
> + * capacity.

Would be useful to know how wide @cpus is, typically. Is that the power
culster?

> + */
> +void sched_update_thermal_pressure(struct cpumask *cpus,
> +				   unsigned long cap_max_freq,
> +				   unsigned long max_freq)
> +{
> +	int cpu;
> +	unsigned long flags = 0;
> +	struct thermal_pressure *cpu_thermal;

You got them in exactly the wrong order here.

> +
> +	for_each_cpu(cpu, cpus) {
> +		cpu_thermal = per_cpu(thermal_pressure_cpu, cpu);
> +		if (!cpu_thermal)
> +			return;
> +		spin_lock_irqsave(&cpu_thermal->lock, flags);
> +		thermal_pressure_update(cpu_thermal, cap_max_freq, max_freq, 1);
> +	}
> +}

That's just horrible style. Move the unlock out of
thermal_pressure_update() such that lock and unlock are in the same
function.