From mboxrd@z Thu Jan  1 00:00:00 1970
Return-Path: <linux-kernel-owner@vger.kernel.org>
Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand
        id S1751420AbdBOOQz (ORCPT <rfc822;w@1wt.eu>);
        Wed, 15 Feb 2017 09:16:55 -0500
Received: from foss.arm.com ([217.140.101.70]:56100 "EHLO foss.arm.com"
        rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP
        id S1750791AbdBOOQy (ORCPT <rfc822;linux-kernel@vger.kernel.org>);
        Wed, 15 Feb 2017 09:16:54 -0500
Date: Wed, 15 Feb 2017 14:16:51 +0000
From: Juri Lelli <juri.lelli@arm.com>
To: Daniel Bristot de Oliveira <bristot@redhat.com>
Cc: Luca Abeni <luca.abeni@santannapisa.it>,
        Steven Rostedt <rostedt@goodmis.org>, linux-kernel@vger.kernel.org,
        Ingo Molnar <mingo@redhat.com>, Peter Zijlstra <peterz@infradead.org>,
        Tommaso Cucinotta <tommaso.cucinotta@sssup.it>,
        Mike Galbraith <efault@gmx.de>,
        Romulo Silva de Oliveira <romulo.deoliveira@ufsc.br>
Subject: Re: [PATCH 3/2] sched/deadline: Use deadline instead of period when
 calculating overflow
Message-ID: <20170215141651.GF1368@e106622-lin>
References: <cover.1487003778.git.bristot@redhat.com>
 <20170214142848.4e62a91f@gandalf.local.home>
 <20170214234926.6b415428@sweethome>
 <20170214191417.4dd96145@gandalf.local.home>
 <20170215084003.4d123e5b@luca>
 <20170215102919.GA1368@e106622-lin>
 <20170215133136.664c1bfe@luca>
 <20170215125925.GD1368@e106622-lin>
 <0b3af651-ad0d-e74b-ea02-f8706ad13bbb@redhat.com>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <0b3af651-ad0d-e74b-ea02-f8706ad13bbb@redhat.com>
User-Agent: Mutt/1.5.21 (2010-09-15)
Sender: linux-kernel-owner@vger.kernel.org
List-ID: <linux-kernel.vger.kernel.org>
X-Mailing-List: linux-kernel@vger.kernel.org

On 15/02/17 14:33, Daniel Bristot de Oliveira wrote:
> On 02/15/2017 01:59 PM, Juri Lelli wrote:
> > Actually, another thing that we noticed, talking on IRC with Peter, is
> > that we seem to be replenishing differently on different occasions:
> 
> When a task is awakened (not by the replenishment timer), it is not
> possible to know if the absolute deadline var stores the absolute
> deadline of activation which took place in the instant
> (current time) - dl_period.
> 
> Therefore, assuming the next deadline is one dl_deadline away from now
> is correct.
> 
> IOW: that is a sporadic activation - the task is activated after at
> least minimum inter-arrival time between activation/replenishment:
> 
> >  - on wakeup (if overflowing) we do
> > 
> >    dl_se->deadline = rq_clock(rq) + pi_se->dl_deadline;
> >    dl_se->runtime = pi_se->dl_runtime;
> 
> 
> In the replenishment timer, it is known that the absolute deadline
> instant of the previous activation is in the deadline var. So
> putting the absolute deadline one dl_period away is correct [1].
> 
> Another point is that this case avoids creating time drift due
> to latencies. For instance, in the case of a 1 ms delay of the timer
> (interrupts disabled?), the wakeup replenishment would push the
> absolute a relative deadline + 1 ms away from the previous deadline.
> 
> IOW: the replenishment timer makes the periodic case - a fixed time
> offset from the previous activation/replenishment.
> 
> >  - when the replenishment timer fires (un-thottle and with runtime < 0)
> > 
> >    dl_se->deadline += pi_se->dl_period;
> >    dl_se->runtime += pi_se->dl_runtime;
> 
> So I think it is correct. Am I missing something?
> 

Nope, you are right, no problems here.

Thanks,

- Juri