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

From: Luca Abeni
Date: Tue Dec 15 2015 - 08:22:04 EST

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
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 :)


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