linux-kernel - Re: [PATCH] sched/deadline: Add sched

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Message-ID: <52E6568F.9040802@unitn.it>
Date:	Mon, 27 Jan 2014 13:52:31 +0100
From:	Luca Abeni <luca.abeni@...tn.it>
To:	Henrik Austad <henrik@...tad.us>
CC:	Juri Lelli <juri.lelli@...il.com>, peterz@...radead.org,
	tglx@...utronix.de, mingo@...hat.com, rostedt@...dmis.org,
	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,
	tommaso.cucinotta@...up.it, nicola.manica@...i.unitn.it,
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	paulmck@...ux.vnet.ibm.com, raistlin@...ux.it,
	insop.song@...il.com, liming.wang@...driver.com, jkacur@...hat.com,
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	bruce.ashfield@...driver.com, linux-doc@...r.kernel.org,
	rob@...dley.net
Subject: Re: [PATCH] sched/deadline: Add sched_dl documentation

On 01/27/2014 01:40 PM, Henrik Austad wrote:
[...]
>>> Current runtime: time spent running _this_ period? or is _remaining_
>>> runtime this period? I get the feeling it's the latter.
>>>
>>> So, roughly, it is the ration
>>>
>>>        remaining_runtime / relative_time_to_deadline
>>>
>>> which needs to be greater than the assigned CPU bandwidth, and if so, the
>>> budget should be replensihed?
>>>
>>> Shouldn't there be something about not refilling the budget before a new
>>> period has started?
>> Uh... Maybe the description above can be improved :)
>> Do you think that using "remaining runtime" instead of "current runtime"
>> would help? If yes, I'll make this change.
>
> Yes, in my vocabularly, "remaining" != "current" :), so changing to
> 'remaining runtime' would be nice.
Ok; I'll make this change.


>> Also, I see that some of your questions are answered by some items below...
>
> Yes, but I left the comments to indicate that the order was a bit
> confusing.
>
>> Do you think that changing the order of the items in the presentation would
>> improve the readability? If you suggest a better ordering, I'll try to
>> rewrite the algorithm's description according to it.
>
> Could be, at least the ratio-caclulation was a bit confusing until I'd read
> the entire section.
>
> My preferred order (I've just cut'n'pased from the original email here)
>
> +  - The state of the task is described by a "scheduling deadline", and
> +    a "current runtime". These two parameters are initially set to 0;
BTW, maybe some of the confusion can be avoided by explaining what the
"remaining runtime" is here... Something like:
- The state of the task is described by a "scheduling deadline", and
   a "current runtime" (representing the amount of execution time that
   the task can use before the scheduling deadline). These two parameters
   are initially set to 0;

Can something like this help? If yes, I'll update the document.


[...]
> +  - When a SCHED_DEADLINE task wakes up (becomes ready for execution),
> +    the scheduler checks if
> +
> +                    current runtime                runtime
> +         ---------------------------------- > ----------------
> +         scheduling deadline - current time         period
> +
> +    then, if the scheduling deadline is smaller than the current time, or
> +    this condition is verified, the scheduling deadline and the
> +    current budget are re-initialised as
> +
> +         scheduling deadline = current time + deadline
> +         current runtime = runtime
> +
> +    otherwise, the scheduling deadline and the current runtime are
> +    left unchanged;
> +
>
> Emphasis on -my- preferred order. :)
Ok; let's see what other people think, and then we decide the items'
order.


> Either way, I'm quite happy with this documentation-update, this is just
> nitpick :)
Ok, good.


			Thanks,
				Luca

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