linux-kernel - Re: [PATCH v10 07/11] sched: get CPU's usage statistic

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Message-ID: <CAKfTPtAzqkSeys=BbXX-CJuVD2NAfQv7nLT0oi4SYKmwJM3vLQ@mail.gmail.com>
Date:	Fri, 27 Mar 2015 16:37:45 +0100
From:	Vincent Guittot <vincent.guittot@...aro.org>
To:	Xunlei Pang <pang.xunlei@...aro.org>
Cc:	Peter Zijlstra <peterz@...radead.org>,
	Ingo Molnar <mingo@...nel.org>,
	lkml <linux-kernel@...r.kernel.org>,
	Preeti U Murthy <preeti@...ux.vnet.ibm.com>,
	Morten Rasmussen <Morten.Rasmussen@....com>,
	Kamalesh Babulal <kamalesh@...ux.vnet.ibm.com>,
	Rik van Riel <riel@...hat.com>,
	Linaro Kernel Mailman List <linaro-kernel@...ts.linaro.org>,
	Mike Galbraith <efault@....de>,
	Dietmar Eggemann <dietmar.eggemann@....com>
Subject: Re: [PATCH v10 07/11] sched: get CPU's usage statistic

On 27 March 2015 at 16:12, Xunlei Pang <pang.xunlei@...aro.org> wrote:
> Hi Vincent,
>
> On 27 February 2015 at 23:54, Vincent Guittot
> <vincent.guittot@...aro.org> wrote:
>> Monitor the usage level of each group of each sched_domain level. The usage is
>> the portion of cpu_capacity_orig that is currently used on a CPU or group of
>> CPUs. We use the utilization_load_avg to evaluate the usage level of each
>> group.
>>
>> The utilization_load_avg only takes into account the running time of the CFS
>> tasks on a CPU with a maximum value of SCHED_LOAD_SCALE when the CPU is fully
>> utilized. Nevertheless, we must cap utilization_load_avg which can be temporaly
>> greater than SCHED_LOAD_SCALE after the migration of a task on this CPU and
>> until the metrics are stabilized.
>>
>> + * at 121% + CPU1 usage at 80%) whereas CPU1 has 20% of available capacity/
>> + */
>> +static int get_cpu_usage(int cpu)
>> +{
>> +       unsigned long usage = cpu_rq(cpu)->cfs.utilization_load_avg;
>> +       unsigned long capacity = capacity_orig_of(cpu);
>> +
>> +       if (usage >= SCHED_LOAD_SCALE)
>> +               return capacity;
>
> Can "capacity" be greater than SCHED_LOAD_SCALE?
> Why use SCHED_LOAD_SCALE instead of "capacity" in this judgement?

Yes, SCHED_LOAD_SCALE is the default value but the capacity can be in
the range [1536:512] for arm as an example

>
> -Xunlei
>
>> +
>> +       return (usage * capacity) >> SCHED_LOAD_SHIFT;
>> +}
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