From: Daniel Lezcano <daniel.lezcano@linaro.org>
To: Lukasz Luba <lukasz.luba@arm.com>
Cc: rafael@kernel.org, linux-kernel@vger.kernel.org,
linux-pm@vger.kernel.org
Subject: Re: [PATCH 5/5] powercap/drivers/dtpm: Scale the power with the load
Date: Tue, 9 Mar 2021 20:03:50 +0100 [thread overview]
Message-ID: <e1dac038-2100-abdb-2ffe-d0d93952ca21@linaro.org> (raw)
In-Reply-To: <c30701f5-c1f8-cb5c-8791-f4068fb1bc14@arm.com>
Hi Lukasz,
thanks for your comments, one question below.
On 09/03/2021 11:01, Lukasz Luba wrote:
[ ... ]
>> +static u64 scale_pd_power_uw(struct cpumask *cpus, u64 power)
>
> renamed 'cpus' into 'pd_mask', see below
>
>> +{
>> + unsigned long max, util;
>> + int cpu, load = 0;
>
> IMHO 'int load' looks odd when used with 'util' and 'max'.
> I would put in the line above to have them all the same type and
> renamed to 'sum_util'.
>
>> +
>> + for_each_cpu(cpu, cpus) {
>
> I would avoid the temporary CPU mask in the get_pd_power_uw()
> with this modified loop:
>
> for_each_cpu_and(cpu, pd_mask, cpu_online_mask) {
>
>
>> + max = arch_scale_cpu_capacity(cpu);
>> + util = sched_cpu_util(cpu, max);
>> + load += ((util * 100) / max);
>
> Below you can find 3 optimizations. Since we are not in the hot
> path here, it's up to if you would like to use all/some of them
> or just ignore.
>
> 1st optimization.
> If we use 'load += (util << 10) / max' in the loop, then
> we could avoid div by 100 and use a right shift:
> (power * load) >> 10
>
> 2nd optimization.
> Since we use EM CPU mask, which span all CPUs with the same
> arch_scale_cpu_capacity(), you can avoid N divs inside the loop
> and do it once, below the loop.
>
> 3rd optimization.
> If we just simply add all 'util' into 'sum_util' (no mul or div in
> the loop), then we might just have simple macro
>
> #define CALC_POWER_USAGE(power, sum_util, max) \
> (((power * (sum_util << 10)) / max) >> 10)
I don't understand the 'max' division, I was expecting here something
like: ((sum_util << 10) / sum_max) >> 10)
no ?
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next prev parent reply other threads:[~2021-03-09 19:04 UTC|newest]
Thread overview: 16+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-03-01 21:21 [PATCH 1/5] powercap/drivers/dtpm: Encapsulate even more the code Daniel Lezcano
2021-03-01 21:21 ` [PATCH 2/5] powercap/drivers/dtpm: Create a registering system Daniel Lezcano
2021-03-09 14:46 ` Lukasz Luba
2021-03-01 21:21 ` [PATCH 3/5] powercap/drivers/dtpm: Simplify the dtpm table Daniel Lezcano
2021-03-09 15:02 ` Lukasz Luba
2021-03-01 21:21 ` [PATCH 4/5] powercap/drivers/dtpm: Use container_of instead of a private data field Daniel Lezcano
2021-03-09 15:17 ` Lukasz Luba
2021-03-01 21:21 ` [PATCH 5/5] powercap/drivers/dtpm: Scale the power with the load Daniel Lezcano
2021-03-09 10:01 ` Lukasz Luba
2021-03-09 19:03 ` Daniel Lezcano [this message]
2021-03-09 20:44 ` Lukasz Luba
2021-03-09 19:22 ` Daniel Lezcano
2021-03-08 19:31 ` [PATCH 1/5] powercap/drivers/dtpm: Encapsulate even more the code Daniel Lezcano
2021-03-08 19:55 ` Lukasz Luba
2021-03-08 21:20 ` Daniel Lezcano
2021-03-09 14:02 ` Lukasz Luba
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