Subject: Re: [RFCv6 PATCH 09/10] sched: deadline: use deadline bandwidth in
 scale_rt_capacity
To: Peter Zijlstra <peterz@infradead.org>
References: <1449641971-20827-1-git-send-email-smuckle@linaro.org>
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 <20151214221231.39b5bc4e@luca-1225C>
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Cc: Vincent Guittot <vincent.guittot@linaro.org>,
        Steve Muckle <steve.muckle@linaro.org>, Ingo Molnar <mingo@redhat.com>,
        linux-kernel <linux-kernel@vger.kernel.org>,
        "linux-pm@vger.kernel.org" <linux-pm@vger.kernel.org>,
        Morten Rasmussen <morten.rasmussen@arm.com>,
        Dietmar Eggemann <dietmar.eggemann@arm.com>,
        Juri Lelli <Juri.Lelli@arm.com>,
        Patrick Bellasi <patrick.bellasi@arm.com>,
        Michael Turquette <mturquette@baylibre.com>
From: Luca Abeni <luca.abeni@unitn.it>
Message-ID: <567013F4.8010301@unitn.it>
Date: Tue, 15 Dec 2015 14:21:56 +0100
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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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