linux-kernel - Re: [RFC PATCH v6 6/9] thermal: cpu_cooling: implement the power cooling device API

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Date:	Wed, 28 Jan 2015 01:23:33 -0400
From:	Eduardo Valentin <edubezval@...il.com>
To:	Javi Merino <javi.merino@....com>
Cc:	linux-pm@...r.kernel.org, linux-kernel@...r.kernel.org,
	punit.agrawal@....com, broonie@...nel.org,
	Zhang Rui <rui.zhang@...el.com>
Subject: Re: [RFC PATCH v6 6/9] thermal: cpu_cooling: implement the power
 cooling device API


Hello Javi,

On Fri, Dec 05, 2014 at 07:04:17PM +0000, Javi Merino wrote:
> Add a basic power model to the cpu cooling device to implement the
> power cooling device API.  The power model uses the current frequency,
> current load and OPPs for the power calculations.  The cpus must have
> registered their OPPs using the OPP library.
> 
> Cc: Zhang Rui <rui.zhang@...el.com>
> Cc: Eduardo Valentin <edubezval@...il.com>
> Signed-off-by: Punit Agrawal <punit.agrawal@....com>
> Signed-off-by: Javi Merino <javi.merino@....com>

<big cut>

> +
> +/**
> + * get_load() - get load for a cpu since last updated
> + * @cpufreq_device:	&struct cpufreq_cooling_device for this cpu
> + * @cpu:	cpu number
> + *
> + * Return: The average load of cpu @cpu in percentage since this
> + * function was last called.
> + */
> +static u32 get_load(struct cpufreq_cooling_device *cpufreq_device, int cpu)
> +{
> +	u32 load;
> +	u64 now, now_idle, delta_time, delta_idle;
> +
> +	now_idle = get_cpu_idle_time(cpu, &now, 0);
> +	delta_idle = now_idle - cpufreq_device->time_in_idle[cpu];
> +	delta_time = now - cpufreq_device->time_in_idle_timestamp[cpu];
> +
> +	if (delta_time <= delta_idle)
> +		load = 0;
> +	else
> +		load = div64_u64(100 * (delta_time - delta_idle), delta_time);
> +
> +	cpufreq_device->time_in_idle[cpu] = now_idle;
> +	cpufreq_device->time_in_idle_timestamp[cpu] = now;
> +
> +	return load;
> +}

<cut>

>  
> +/**
> + * cpufreq_get_actual_power() - get the current power
> + * @cdev:	&thermal_cooling_device pointer
> + *
> + * Return the current power consumption of the cpus in milliwatts.
> + */
> +static u32 cpufreq_get_actual_power(struct thermal_cooling_device *cdev)
> +{
> +	unsigned long freq;
> +	int cpu;
> +	u32 static_power, dynamic_power, total_load = 0;
> +	struct cpufreq_cooling_device *cpufreq_device = cdev->devdata;
> +
> +	freq = cpufreq_quick_get(cpumask_any(&cpufreq_device->allowed_cpus));
> +
> +	for_each_cpu(cpu, &cpufreq_device->allowed_cpus) {
> +		u32 load;
> +
> +		if (cpu_online(cpu))
> +			load = get_load(cpufreq_device, cpu);
> +		else
> +			load = 0;
> +
> +		total_load += load;
> +	}
> +
> +	cpufreq_device->last_load = total_load;
> +
> +	static_power = get_static_power(cpufreq_device, freq);
> +	dynamic_power = get_dynamic_power(cpufreq_device, freq);
> +
> +	return static_power + dynamic_power;
> +}

With respect to load computation vs. frequency usage vs. power
estimation, while getting actual power for a given interval T. What if
in interval T, we have used, say, 3 different cpu frequencies, and the
load on the first was 50%, on the second 80%, and on the last frequency,
the load was 60%, what should be the right load value for computing the
actual power? 

I mean, we are using the total idle time for a given interval, but 1 -
idle not always seams to reflect actual load on different opps, if opps
change over time within T time interval window.

BR,


BR,

Eduardo Valentin

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