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

[Juri Lelli]

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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