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

[Peter Zijlstra]

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?

> +
> +       return 1;
> +} 


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