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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>
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 <20170504142329.wanerqq5nsmu3blr@hirez.programming.kicks-ass.net>
From: Daniel Bristot de Oliveira <bristot@redhat.com>
Message-ID: <9eb70e53-0d8a-94e8-7da4-b577aaafd56e@redhat.com>
Date: Thu, 11 May 2017 19:07:01 +0200
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On 05/04/2017 04:23 PM, Peter Zijlstra wrote:
> On Thu, May 04, 2017 at 04:17:21PM +0200, Peter Zijlstra wrote:
>> On Mon, Apr 24, 2017 at 05:18:35PM +0200, Daniel Bristot de Oliveira wrote:
>>> +static void
>>> +update_dl_revised_wakeup(struct sched_dl_entity *dl_se, struct rq *rq)
>>> +{
>>> +	u64 density = div64_u64(dl_se->dl_runtime << 20, dl_se->dl_deadline);
>>> +	u64 laxity = dl_se->deadline - rq_clock(rq);
>>> +
>>> +	BUG_ON(laxity < 0);
>> Compiler will make that go away, by virtue of laxity being unsigned.
> Also, so we want that to BUG (or even WARN) in a soft RT setting.
> Remember, GEDF does not guarantee we make our deadlines.

The point is that, a task with laxity < 0 should be throttled before
this point by:

df8eac8cafce ("sched/deadline: Throttle a constrained deadline task
activated after the deadline")

Arrive here with (laxity < 0) meas that we skipped that check.

>> We use two difference CBS rules:
> _different_, clearly I cannot type anymore either ;-)

ops... :-)

-- Daniel