Re: [PATCH] sched/deadline: Add sched_dl documentation

[Luca Abeni]

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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