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

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Date:	Thu, 12 Apr 2012 20:56:04 +0800
From:	Hillf Danton <dhillf@...il.com>
To:	Steven Rostedt <rostedt@...dmis.org>
Cc:	Juri Lelli <juri.lelli@...il.com>, peterz@...radead.org,
	tglx@...utronix.de, mingo@...hat.com, cfriesen@...tel.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, fcheccon@...per.es
Subject: Re: [PATCH 06/16] sched: SCHED_DEADLINE push and pull logic

On Thu, Apr 12, 2012 at 8:51 PM, Steven Rostedt <rostedt@...dmis.org> wrote:
> On Thu, 2012-04-12 at 20:28 +0800, Hillf Danton wrote:
>> On Wed, Apr 11, 2012 at 10:10 PM, Steven Rostedt <rostedt@...dmis.org> wrote:
>> > On Fri, 2012-04-06 at 21:39 +0800, Hillf Danton wrote:
>> >
>> >> > +static void inc_dl_migration(struct sched_dl_entity *dl_se, struct dl_rq *dl_rq)
>> >> > +{
>> >> > +       dl_rq = &rq_of_dl_rq(dl_rq)->dl;
>> >> > +
>> >> > +       dl_rq->dl_nr_total++;
>> >> > +       if (dl_se->nr_cpus_allowed > 1)
>> >> > +               dl_rq->dl_nr_migratory++;
>> >> > +
>> >> > +       update_dl_migration(dl_rq);
>> >>
>> >>       if (dl_se->nr_cpus_allowed > 1) {
>> >>               dl_rq->dl_nr_migratory++;
>> >>               /* No change in migratory, no update of migration */
>> >
>> > This is not true. As dl_nr_total changed. If there was only one dl task
>> > queued that can migrate, and then another dl task is queued but this
>> > task can not migrate, the update_dl_migration still needs to be called.
>> > As dl_nr_migratory would be 1, but now dl_nr_total > 1. This means we
>> > are now overloaded.
>> >
>
> You're speaking in riddles.
>
>>       if (2 == dl_nr_migratory + dl_nr_total)
>>               rq was not overloaded;
>>
>>       after enqueuing a deadline task that is not migratory,
>
> Now rq would be overloaded because:
>
>        dl_nr_migratory + dl_nr_total == 3
>

Which is the current task, and where?

>
>>
>>       if (current task is not preempted)
>>               rq remains not overloaded;
>
> s/not//
>
>>
>>       else if (current task is not pushed out) {
>>               if (rq is not overloaded)
>>                       maintenance of overloaded is __corrupted__;
>>       }
>>
>> btw, same behavior in RTS?
>
> I still don't understand what you are saying.
>
> I can see your scenario happening with the change you are suggesting
> though.
>
> -- Steve
>
>
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