linux-kernel - Re: [PATCH 05/16] sched: SCHED_DEADLINE policy implementation.

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Message-ID: <4F95C8AF.2040606@sssup.it>
Date:	Mon, 23 Apr 2012 22:25:03 +0100
From:	Tommaso Cucinotta <tommaso.cucinotta@...up.it>
To:	Juri Lelli <juri.lelli@...il.com>
CC:	Peter Zijlstra <peterz@...radead.org>, tglx@...utronix.de,
	mingo@...hat.com, rostedt@...dmis.org, cfriesen@...tel.com,
	oleg@...hat.com, fweisbec@...il.com, darren@...art.com,
	johan.eker@...csson.com, p.faure@...tech.ch,
	linux-kernel@...r.kernel.org, claudio@...dence.eu.com,
	michael@...rulasolutions.com, fchecconi@...il.com,
	nicola.manica@...i.unitn.it, luca.abeni@...tn.it,
	dhaval.giani@...il.com, hgu1972@...il.com,
	paulmck@...ux.vnet.ibm.com, raistlin@...ux.it,
	insop.song@...csson.com, liming.wang@...driver.com
Subject: Re: [PATCH 05/16] sched: SCHED_DEADLINE policy implementation.

Il 23/04/2012 11:37, Juri Lelli ha scritto:
> On 04/23/2012 12:31 PM, Peter Zijlstra wrote:
>> On Fri, 2012-04-06 at 09:14 +0200, Juri Lelli wrote:
>>> +       dl_se->deadline = rq->clock + dl_se->dl_deadline;
>>
>> You might want to use rq->clock_task, this clock excludes times spend in
>> hardirq context and steal-time (when paravirt).
>>
>> Then again, it might not want to use that.. but its something you might
>> want to consider and make explicit by means of a comment.
>
> Yes, I planned a consistency check for the use of clock/clock_task
> throughout the code, but it seems I then forgot it.
> Planned for the next iteration :-).

unless I'm mistaken, there are 3 repetitions of this block in 05/16:

+		dl_se->deadline = rq->clock + dl_se->dl_deadline;
+		dl_se->runtime = dl_se->dl_runtime;


perhaps enclosing them into a function (e.g., reset_from_now() or 
similar) may help to keep consistency...

Another thing: I cannot get the real difference between rq->clock and 
rq->task_clock.
If task_clock is a kind of CLOCK_MONOTONIC thing that increases only 
when the task (or any task) is scheduled, then you don't want to use 
that here.
Here you need to set the new ->deadline to an absolute time, so I guess 
the regular rq->clock is what you need, isn't it ?

Hope I didn't say too much nonsense.

     T.

-- 
Tommaso Cucinotta, Computer Engineering PhD, Researcher
ReTiS Lab, Scuola Superiore Sant'Anna, Pisa, Italy
Tel +39 050 882 024, Fax +39 050 882 003
http://retis.sssup.it/people/tommaso

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