linux-kernel - Re: [PATCH 05/16] sched: SCHED_DEADLINE policy implementation.

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Message-ID: <4F957723.2000000@gmail.com>
Date:	Mon, 23 Apr 2012 17:37:07 +0200
From:	Juri Lelli <juri.lelli@...il.com>
To:	Peter Zijlstra <peterz@...radead.org>
CC:	tglx@...utronix.de, mingo@...hat.com, rostedt@...dmis.org,
	cfriesen@...tel.com, oleg@...hat.com, fweisbec@...il.com,
	darren@...art.com, johan.eker@...csson.com, p.faure@...tech.ch,
	linux-kernel@...r.kernel.org, claudio@...dence.eu.com,
	michael@...rulasolutions.com, fchecconi@...il.com,
	tommaso.cucinotta@...up.it, nicola.manica@...i.unitn.it,
	luca.abeni@...tn.it, dhaval.giani@...il.com, hgu1972@...il.com,
	paulmck@...ux.vnet.ibm.com, raistlin@...ux.it,
	insop.song@...csson.com, liming.wang@...driver.com
Subject: Re: [PATCH 05/16] sched: SCHED_DEADLINE policy implementation.

On 04/23/2012 05:15 PM, Peter Zijlstra wrote:
> On Fri, 2012-04-06 at 09:14 +0200, Juri Lelli wrote:
>> +static
>> +int dl_runtime_exceeded(struct rq *rq, struct sched_dl_entity *dl_se)
>> +{
>> +       int dmiss = dl_time_before(dl_se->deadline, rq->clock);
>> +       int rorun = dl_se->runtime<= 0;
>> +
>> +       if (!rorun&&  !dmiss)
>> +               return 0;
>> +
>> +       /*
>> +        * If we are beyond our current deadline and we are still
>> +        * executing, then we have already used some of the runtime of
>> +        * the next instance. Thus, if we do not account that, we are
>> +        * stealing bandwidth from the system at each deadline miss!
>> +        */
>> +       if (dmiss) {
>> +               dl_se->runtime = rorun ? dl_se->runtime : 0;
>> +               dl_se->runtime -= rq->clock - dl_se->deadline;
>> +       }
>
> So ideally this can't happen, but since we already leak time from the
> system through means of hardirq / kstop / context-switch-overhead /
> clock-jitter etc.. we avoid the error accumulating?
>

Yep, seems fair :-).
  
>> +
>> +       return 1;
>> +}
>
>

Thanks,

- Juri
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