linux-kernel - Re: [PATCH RFC] sched/deadline: Use the revised wakeup rule for suspending constrained dl tasks

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Date:   Thu, 11 May 2017 19:08:22 +0200
From:   Daniel Bristot de Oliveira <bristot@...hat.com>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     Ingo Molnar <mingo@...hat.com>, Xunlei Pang <xpang@...hat.com>,
        Juri Lelli <juri.lelli@....com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Luca Abeni <luca.abeni@...tannapisa.it>,
        Tommaso Cucinotta <tommaso.cucinotta@...up.it>,
        Romulo Silva de Oliveira <romulo.deoliveira@...c.br>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH RFC] sched/deadline: Use the revised wakeup rule for
 suspending constrained dl tasks

On 05/04/2017 04:26 PM, Peter Zijlstra wrote:
> On Thu, May 04, 2017 at 04:17:21PM +0200, Peter Zijlstra wrote:
>> We use two difference CBS rules:
>>
>>  1) the original CBS rule for implicit deadline tasks;
>>  2) the revised CBS rule for constrained deadline tasks.
>>> @@ -500,6 +550,14 @@ static void update_dl_entity(struct sched_dl_entity *dl_se,
>>>  
>>>  	if (dl_time_before(dl_se->deadline, rq_clock(rq)) ||
>>>  	    dl_entity_overflow(dl_se, pi_se, rq_clock(rq))) {
>>> +
>>> +		if (unlikely(dl_is_constrained(dl_se) &&
>>> +		    !dl_time_before(dl_se->deadline, rq_clock(rq)) &&
>>> +		    !dl_se->dl_boosted)){
>>> +			update_dl_revised_wakeup(dl_se, rq);
>>> +			return;
>>> +		}
>>> +
>>>  		dl_se->deadline = rq_clock(rq) + pi_se->dl_deadline;
>>>  		dl_se->runtime = pi_se->dl_runtime;
>>>  	}
> That comment above does not match the code. We can still use the
> original CBS rule for constrained tasks.
> 
> We only use the revised CBS rule when the constrained task hasn't missed
> its deadline yet.

Correct. I will improve the explanation.

Thank you very much for all comments :-)

-- Daniel