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SubjectRe: [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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