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Subject: Re: [PATCH RFC] sched/deadline: Use the revised wakeup rule for
 suspending constrained dl tasks
To: Peter Zijlstra <peterz@infradead.org>
Cc: Ingo Molnar <mingo@redhat.com>, Xunlei Pang <xpang@redhat.com>,
        Juri Lelli <juri.lelli@arm.com>, Steven Rostedt <rostedt@goodmis.org>,
        Luca Abeni <luca.abeni@santannapisa.it>,
        Tommaso Cucinotta <tommaso.cucinotta@sssup.it>,
        Romulo Silva de Oliveira <romulo.deoliveira@ufsc.br>,
        linux-kernel@vger.kernel.org
References: <5c6933890ea6daa3b4edb4983b0c6f094ad3903d.1493045834.git.bristot@redhat.com>
 <20170504141721.5f6tlayqwyq4cxnw@hirez.programming.kicks-ass.net>
 <20170504142632.fdnwfqxcas7d3t7x@hirez.programming.kicks-ass.net>
From: Daniel Bristot de Oliveira <bristot@redhat.com>
Message-ID: <94f331e7-913e-04c8-c065-765d39c851f7@redhat.com>
Date: Thu, 11 May 2017 19:08:22 +0200
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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