linux-kernel - Re: [RFCv6 PATCH 09/10] sched: deadline: use deadline bandwidth in scale_rt

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Date:	Tue, 15 Dec 2015 14:21:56 +0100
From:	Luca Abeni <luca.abeni@...tn.it>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	Vincent Guittot <vincent.guittot@...aro.org>,
	Steve Muckle <steve.muckle@...aro.org>,
	Ingo Molnar <mingo@...hat.com>,
	linux-kernel <linux-kernel@...r.kernel.org>,
	"linux-pm@...r.kernel.org" <linux-pm@...r.kernel.org>,
	Morten Rasmussen <morten.rasmussen@....com>,
	Dietmar Eggemann <dietmar.eggemann@....com>,
	Juri Lelli <Juri.Lelli@....com>,
	Patrick Bellasi <patrick.bellasi@....com>,
	Michael Turquette <mturquette@...libre.com>
Subject: Re: [RFCv6 PATCH 09/10] sched: deadline: use deadline bandwidth in
 scale_rt_capacity

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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