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    Subject[RFD PATCH 0/5] SCHED_DEADLINE freq/cpu invariance and OPP selection
    Date
    Hi,

    this is a very exploratory set implementing frequency/cpu invariance and OPP
    selection for SCHED_DEADLINE. The set has been slightly tested on a Juno
    platform. While the actual implementation is very premature, I'm posting this
    early to facilitate discussion at OSPM-summit [1].

    Results of the testing, highlighting why these features are useful are
    available here:

    - without the set
    https://gist.github.com/a6e3ee99cec32e00cc537b53cd3d54d2

    - with the set
    https://gist.github.com/1f7d485fc3ce9234fe627dcb53b2935c

    The set is based on tip/sched/core as of today (bc4278987e38) plus a couple of
    schedutil fixes coming from linux-pm/linux-next and Luca's "CPU reclaiming for
    SCHED_DEADLINE" v5 [2].

    Patches high level description:

    o [01-02]/05 add the necessary links to start accounting DEADLINE contribution
    to OPP selection
    o 03/05 it's an hack to make possible (on ARM) to change frequency for
    DEADLINE tasks (that would possibly delay the SCHED_FIFO worker
    kthread); suggestions on how to do this properly are very welcome
    o 04/05 it's a schedutil change that copes with the fact that DEADLINE
    doesn't require periodic OPP selection triggering point
    o 05/05 implements frequency/cpu invariance for tasks' reservation
    parameters*; which basically means that we implement GRUB-PA [3]

    Please have a look. Feedback on how we want to shape this is the sole purpose
    of this posting.

    In case you would like to test this out:

    git://linux-arm.org/linux-jl.git upstream/deadline/freq-rfd

    Best,

    - Juri

    [1] http://retis.sssup.it/ospm-summit/index.html
    [2] https://marc.info/?l=linux-kernel&m=149029880524038
    [3] C. Scordino, G. Lipari, A Resource Reservation Algorithm for Power-Aware
    Scheduling of Periodic and Aperiodic Real-Time Tasks, IEEE Transactions
    on Computers, December 2006.

    * Notice that this currently breaks !CONFIG_SMP, as arch_scale_{freq,cpu}
    _capacity and SCHED_CAPACITY_SCALE are only defined on CONFIG_SMP. Fixing
    this particular issue is straightforward, but we should probably look into
    making frequency scaling (and PELT averages) available on !CONFIG_SMP as well
    (so that schedutil can work on such configurations for example). Since this is
    only an RFD and since a proper rework might be non trivial, I decided to leave
    it out of scope for the time being.

    Juri Lelli (5):
    sched/cpufreq_schedutil: make use of DEADLINE utilization signal
    sched/deadline: move cpu frequency selection triggering points
    sched/cpufreq_schedutil: make worker kthread be SCHED_DEADLINE
    sched/cpufreq_schedutil: always consider all CPUs when deciding next
    freq
    sched/deadline: make bandwidth enforcement scale-invariant

    include/linux/sched.h | 1 +
    include/linux/sched/cpufreq.h | 2 --
    include/uapi/linux/sched.h | 1 +
    kernel/sched/core.c | 19 +++++++++++++++++--
    kernel/sched/cpufreq_schedutil.c | 37 ++++++++++++++++++++++---------------
    kernel/sched/deadline.c | 40 +++++++++++++++++++++++++++++++++-------
    kernel/sched/fair.c | 2 --
    kernel/sched/sched.h | 10 +++++++++-
    8 files changed, 83 insertions(+), 29 deletions(-)

    --
    2.10.0

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