Re: [RFCv6 PATCH 09/10] sched: deadline: use deadline bandwidth in scale_rt_capacity

[Luca Abeni]

On 12/15/2015 01:23 PM, Peter Zijlstra wrote:
> On Tue, Dec 15, 2015 at 09:50:14AM +0100, Luca Abeni wrote:
> > Strictly speaking, the active utilisation must be updated when a task
> > wakes up and when a task sleeps/terminates (but when a task sleeps/terminates
> > you cannot decrease the active utilisation immediately: you have to wait
> > some time because the task might already have used part of its "future
> > utilisation").
> > The active utilisation must not be updated when a task is throttled: a
> > task is throttled when its current runtime is 0, so it already used all
> > of its utilisation for the current period (think about two tasks with
> > runtime=50ms and period 100ms: they consume 100% of the time on a CPU,
> > and when the first task consumed all of its runtime, you cannot decrease
> > the active utilisation).
>
> Hehe, this reminds me of the lag tracking in EEVDF/WF2Q/BFQ etc., that
> had similar issues.
Yes, I remember EEVDF and similar algorithms also needed to keep track of
the current lag (and to reset it at a later time respect to the "task is
blocking" event). I do not remember the exact details, but I "borrowed" the
"0-lag time" name from one of those papers :)


				Luca

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