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Date: Mon, 23 Apr 2012 17:37:07 +0200
From: Juri Lelli <juri.lelli@gmail.com>
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To: Peter Zijlstra <peterz@infradead.org>
CC: tglx@linutronix.de, mingo@redhat.com, rostedt@goodmis.org,
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Subject: Re: [PATCH 05/16] sched: SCHED_DEADLINE policy implementation.
References: <1333696481-3433-1-git-send-email-juri.lelli@gmail.com>  <1333696481-3433-6-git-send-email-juri.lelli@gmail.com> <1335194148.28150.175.camel@twins>
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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