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    SubjectRe: [PATCH 1/3] Added runqueue clock normalized with cpufreq
    On Fri, 2010-12-17 at 19:56 +0100, Dario Faggioli wrote:
    > On Fri, 2010-12-17 at 15:29 +0100, Peter Zijlstra wrote:
    > > Solving the CPUfreq problem involves writing a SCHED_DEADLINE aware
    > > CPUfreq governor. The governor must know about the constraints placed on
    > > the system by the task-set. You simply cannot lower the frequency when
    > > your system is at u=1.
    > >
    > We already did the very same thing (for another EU Project called
    > FRESCOR), although it was done in an userspace sort of daemon. It was
    > also able to consider other "high level" parameters like some estimation
    > of the QoS of each application and of the global QoS of the system.
    > However, converting the basic mechanism into a CPUfreq governor should
    > be easily doable... The only problem is finding the time for that! ;-P

    Ah, I think Harald will solve that for you,.. :)

    > > The simple solution would be to slow down the runtime accounting of
    > > SCHED_DEADLINE tasks by freq/max_freq. So instead of having:
    > >
    > > dl_se->runtime -= delta;
    > >
    > > you do something like:
    > >
    > > dl_se->runtime -= (freq * delta) / max_freq;
    > >
    > > Which auto-magically grows the actual bandwidth, and since the deadlines
    > > are wall-time already it all works out nicely. It also keeps the
    > > overhead inside SCHED_DEADLINE.
    > >
    > And, at least for the meantime, this seems a very very nice solution.
    > The only thing I don't like is that division which would end up in being
    > performed at each tick/update_curr_dl(), but we can try to find out a
    > way to mitigate this, what do you think Harald?

    A simple mult and shift-right should do. You can either pre-compute for
    a platform, or compute the inv multiplier in the cpufreq notifier thing.

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      Last update: 2010-12-17 20:05    [W:0.021 / U:1.484 seconds]
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