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

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Date:   Thu, 4 May 2017 16:23:29 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Daniel Bristot de Oliveira <bristot@...hat.com>
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 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.


> We use two difference CBS rules:

_different_, clearly I cannot type anymore either ;-)