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    SubjectRe: [PATCH 0/3] cpufreq: Replace timers with utilization update callbacks
    On 01/03/16 14:58, Peter Zijlstra wrote:
    > On Fri, Feb 12, 2016 at 03:48:54PM +0100, Vincent Guittot wrote:
    >
    > > Another point to take into account is that the RT tasks will "steal"
    > > the compute capacity that has been requested by the cfs tasks.
    > >
    > > Let takes the example of a CPU with 3 OPP on which run 2 rt tasks A
    > > and B and 1 cfs task C.
    >
    > > Let assume that the real time constraint of RT task A is too agressive
    > > for the lowest OPP0 and that the change of the frequency of the core
    > > is too slow compare to this constraint but the real time constraint of
    > > RT task B can be handle whatever the OPP. System don't have other
    > > choice than setting the cpufreq min freq to OPP1 to be sure that
    > > constraint of task A will be covered at anytime.
    >
    > > Then, we still have 2
    > > possible OPPs. The CFS task asks for compute capacity that fits in
    > > OPP1 but a part of this capacity will be stolen by RT tasks. If we
    > > monitor the load of RT tasks and request capacity for these RT tasks
    > > according to their current utilization, we can decide to switch to
    > > highest OPP2 to ensure that task C will have enough remaining
    > > capacity. A lot of embedded platform faces such kind of use cases
    >
    > Still doesn't make sense. How would you know the constraint of RT task
    > A, and that it cannot be satisfied by OPP0 ? The only information you
    > have in the task model is a static priority.
    >

    But, can't we have the problem Vincent describes if we s/RT/DL/ ?

    Thanks,

    - Juri

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