linux-kernel - Re: [PATCH 06/16] sched: SCHED

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Date:	Thu, 19 Apr 2012 15:44:16 +0200
From:	Juri Lelli <juri.lelli@...il.com>
To:	Steven Rostedt <rostedt@...dmis.org>
CC:	peterz@...radead.org, tglx@...utronix.de, mingo@...hat.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 06/16] sched: SCHED_DEADLINE push and pull logic

On 04/11/2012 06:14 PM, Steven Rostedt wrote:
> On Fri, 2012-04-06 at 09:14 +0200, Juri Lelli wrote:
>
>> +static int latest_cpu_find(struct cpumask *span,
>> +			   struct task_struct *task,
>> +			   struct cpumask *later_mask)
>>   {
>> +	const struct sched_dl_entity *dl_se =&task->dl;
>> +	int cpu, found = -1, best = 0;
>> +	u64 max_dl = 0;
>> +
>> +	for_each_cpu(cpu, span) {
>> +		struct rq *rq = cpu_rq(cpu);
>> +		struct dl_rq *dl_rq =&rq->dl;
>> +
>> +		if (cpumask_test_cpu(cpu,&task->cpus_allowed)&&
>> +		    (!dl_rq->dl_nr_running || dl_time_before(dl_se->deadline,
>> +		     dl_rq->earliest_dl.curr))) {
>> +			if (later_mask)
>> +				cpumask_set_cpu(cpu, later_mask);
>> +			if (!best&&  !dl_rq->dl_nr_running) {
>
> I hate to say this (and I also have yet to look at the patches after
> this) but we should really take into account the RT tasks. It would suck
> to preempt a normal RT task when a non RT task is running on another
> CPU.

Well, this changes in 15/16, but your point remains, and I see it :-).
We are currently reworking the push/pull mechanism (15/16 will most probably
change as well) to speed it up. I agree that it would be nice to take into
accont RT tasks as well, so we'll surely think about it.
   
>> +				best = 1;
>> +				found = cpu;
>> +			} else if (!best&&
>> +				   dl_time_before(max_dl,
>> +						  dl_rq->earliest_dl.curr)) {
>> +				max_dl = dl_rq->earliest_dl.curr;
>> +				found = cpu;
>> +			}
>> +		} else if (later_mask)
>> +			cpumask_clear_cpu(cpu, later_mask);
>> +	}
>> +
>> +	return found;
>> +}
>
>

Thanks,

- Juri
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