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

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Message-ID: <CADcy93WuRMX_PWxSW1k8k0=ArMhvzLo=hX9KiMQbHPrSryeLCA@mail.gmail.com>
Date:	Fri, 27 Mar 2015 23:12:19 +0800
From:	Xunlei Pang <pang.xunlei@...aro.org>
To:	Vincent Guittot <vincent.guittot@...aro.org>
Cc:	Peter Zijlstra <peterz@...radead.org>,
	Ingo Molnar <mingo@...nel.org>,
	lkml <linux-kernel@...r.kernel.org>, preeti@...ux.vnet.ibm.com,
	Morten Rasmussen <Morten.Rasmussen@....com>,
	kamalesh@...ux.vnet.ibm.com, riel@...hat.com,
	Linaro Kernel Mailman List <linaro-kernel@...ts.linaro.org>,
	efault@....de, Dietmar Eggemann <dietmar.eggemann@....com>
Subject: Re: [PATCH v10 07/11] sched: get CPU's usage statistic

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?

-Xunlei

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