linux-kernel - Re: [PATCH v3 5/5] powercap/drivers/dtpm: Scale the power with the load

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Message-ID: <d2a57633-074a-f0c3-25dc-7ebdf8455d2f@arm.com>
Date:   Wed, 10 Mar 2021 11:22:10 +0000
From:   Lukasz Luba <lukasz.luba@....com>
To:     Daniel Lezcano <daniel.lezcano@...aro.org>
Cc:     rafael@...nel.org, linux-kernel@...r.kernel.org,
        linux-pm@...r.kernel.org
Subject: Re: [PATCH v3 5/5] powercap/drivers/dtpm: Scale the power with the
 load



On 3/10/21 11:02 AM, Daniel Lezcano wrote:
> Currently the power consumption is based on the current OPP power
> assuming the entire performance domain is fully loaded.
> 
> That gives very gross power estimation and we can do much better by
> using the load to scale the power consumption.
> 
> Use the utilization to normalize and scale the power usage over the
> max possible power.
> 
> Tested on a rock960 with 2 big CPUS, the power consumption estimation
> conforms with the expected one.
> 
> Before this change:
> 
> ~$ ~/dhrystone -t 1 -l 10000&
> ~$ cat /sys/devices/virtual/powercap/dtpm/dtpm:0/dtpm:0:1/constraint_0_max_power_uw
> 2260000
> 
> After this change:
> 
> ~$ ~/dhrystone -t 1 -l 10000&
> ~$ cat /sys/devices/virtual/powercap/dtpm/dtpm:0/dtpm:0:1/constraint_0_max_power_uw
> 1130000
> 
> ~$ ~/dhrystone -t 2 -l 10000&
> ~$ cat /sys/devices/virtual/powercap/dtpm/dtpm:0/dtpm:0:1/constraint_0_max_power_uw
> 2260000
> 
> Signed-off-by: Daniel Lezcano <daniel.lezcano@...aro.org>
> ---
> 
> V3:
>    - Fixed uninitialized 'cpu' in scaled_power_uw()
> V2:
>    - Replaced cpumask by em_span_cpus
>    - Changed 'util' metrics variable types
>    - Optimized utilization scaling power computation
>    - Renamed parameter name for scale_pd_power_uw()
> ---
>   drivers/powercap/dtpm_cpu.c | 46 +++++++++++++++++++++++++++++++------
>   1 file changed, 39 insertions(+), 7 deletions(-)
> 
> diff --git a/drivers/powercap/dtpm_cpu.c b/drivers/powercap/dtpm_cpu.c
> index ac7f2e7e262f..47854923d958 100644
> --- a/drivers/powercap/dtpm_cpu.c
> +++ b/drivers/powercap/dtpm_cpu.c
> @@ -68,27 +68,59 @@ static u64 set_pd_power_limit(struct dtpm *dtpm, u64 power_limit)
>   	return power_limit;
>   }
>   
> +static u64 scale_pd_power_uw(struct cpumask *pd_mask, u64 power)
> +{
> +	unsigned long max = 0, sum_util = 0;
> +	int cpu;
> +
> +	for_each_cpu_and(cpu, pd_mask, cpu_online_mask) {
> +
> +		/*
> +		 * The capacity is the same for all CPUs belonging to
> +		 * the same perf domain, so a single call to
> +		 * arch_scale_cpu_capacity() is enough. However, we
> +		 * need the CPU parameter to be initialized by the
> +		 * loop, so the call ends up in this block.
> +		 *
> +		 * We can initialize 'max' with a cpumask_first() call
> +		 * before the loop but the bits computation is not
> +		 * worth given the arch_scale_cpu_capacity() just
> +		 * returns a value where the resulting assembly code
> +		 * will be optimized by the compiler.
> +		 */
> +		max = arch_scale_cpu_capacity(cpu);
> +		sum_util += sched_cpu_util(cpu, max);
> +	}
> +
> +	/*
> +	 * In the improbable case where all the CPUs of the perf
> +	 * domain are offline, 'max' will be zero and will lead to an
> +	 * illegal operation with a zero division.
> +	 */
> +	return max ? (power * ((sum_util << 10) / max)) >> 10 : 0;
> +}
> +
>   static u64 get_pd_power_uw(struct dtpm *dtpm)
>   {
>   	struct dtpm_cpu *dtpm_cpu = to_dtpm_cpu(dtpm);
>   	struct em_perf_domain *pd;
> -	struct cpumask cpus;
> +	struct cpumask *pd_mask;
>   	unsigned long freq;
> -	int i, nr_cpus;
> +	int i;
>   
>   	pd = em_cpu_get(dtpm_cpu->cpu);
> -	freq = cpufreq_quick_get(dtpm_cpu->cpu);
>   
> -	cpumask_and(&cpus, cpu_online_mask, to_cpumask(pd->cpus));
> -	nr_cpus = cpumask_weight(&cpus);
> +	pd_mask = em_span_cpus(pd);
> +
> +	freq = cpufreq_quick_get(dtpm_cpu->cpu);
>   
>   	for (i = 0; i < pd->nr_perf_states; i++) {
>   
>   		if (pd->table[i].frequency < freq)
>   			continue;
>   
> -		return pd->table[i].power *
> -			MICROWATT_PER_MILLIWATT * nr_cpus;
> +		return scale_pd_power_uw(pd_mask, pd->table[i].power *
> +					 MICROWATT_PER_MILLIWATT);
>   	}
>   
>   	return 0;
> 

LGTM

Reviewed-by: Lukasz Luba <lukasz.luba@....com>