linux-kernel - Re: [PATCH v2 08/11] sched: get CPU's activity statistic

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Date:	Wed, 4 Jun 2014 14:09:18 +0100
From:	Morten Rasmussen <morten.rasmussen@....com>
To:	Vincent Guittot <vincent.guittot@...aro.org>
Cc:	Peter Zijlstra <peterz@...radead.org>,
	"mingo@...nel.org" <mingo@...nel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux@....linux.org.uk" <linux@....linux.org.uk>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	"preeti@...ux.vnet.ibm.com" <preeti@...ux.vnet.ibm.com>,
	"efault@....de" <efault@....de>,
	"nicolas.pitre@...aro.org" <nicolas.pitre@...aro.org>,
	"linaro-kernel@...ts.linaro.org" <linaro-kernel@...ts.linaro.org>,
	"daniel.lezcano@...aro.org" <daniel.lezcano@...aro.org>
Subject: Re: [PATCH v2 08/11] sched: get CPU's activity statistic

On Wed, Jun 04, 2014 at 12:52:46PM +0100, Vincent Guittot wrote:
> On 4 June 2014 13:23, Morten Rasmussen <morten.rasmussen@....com> wrote:
> > I get:
> >
> > A: 15/40 ms = 37.5%
> > B: 20/40 ms = 50%
> >
> > Schedule:
> >
> >    | 5 ms | 5 ms | 5 ms | 5 ms | 5 ms | 5 ms | 5 ms | 5 ms | 5 ms |
> > A:   run     rq     run  ----------- sleeping -------------  run
> > B:   rq      run    rq    run   ---- sleeping -------------  rq
> >
> >> and CPU runnable will be 60% too
> >
> > rq->avg.runnable_avg_sum should be 50%. You have two tasks running for
> > 20 ms every 40 ms.
> >
> > Right?
> 
> ok, i see the misunderstood.
> it's depends of what we mean by runnable. You take the % of time
> whereas i take the runnable_avg_sum/period

Right. There is a difference.

> 
> so A is on_rq 15/40 ms = 37.5% of the time which gives a
> runnable_avg_sum/runnable_avg_period of 47%
> B is on_rq  20/40 ms = 50% of the time which gives a
> runnable_avg_sum/runnable_avg_period of 60%
> and CPU has a task on its rq 20/40ms = 50% of the time which gives a
> runnable_avg_sum/runnable_avg_period of 60%

Yes, that seems about right.
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