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    Subject[PATCH 0/3] Create sched_select_cpu() and use it in workqueues
    In order to save power, it would be useful to schedule work onto non-IDLE cpus
    instead of waking up an IDLE one.

    To achieve this, we need scheduler to guide kernel frameworks (like: timers &
    workqueues) on which is the most preferred CPU that must be used for these

    This patchset is about implementing this concept.

    The first patch adds sched_select_cpu() routine which returns the preferred cpu
    which is non-idle. It accepts max level of sched domain, upto which we can
    choose a CPU from. It can accept following options: SD_SIBLING, SD_MC, SD_BOOK,
    SD_CPU or SD_NUMA.

    Second and Third patch are about adapting this change in workqueue framework.

    Earlier discussions over this concept were done at last LPC:


    Test case 1:
    - Performed on TC2 with ubuntu-devel
    - Boot TC2 and run
    $ trace-cmd record -e workqueue_execute_start

    This will trace only the points, where the work actually runs.

    Do, this for 150 seconds.

    Domain 0: CPU 0-1
    Domain 1: CPU 2-4

    Base Kernel: Without my modifications:

    CPU No. of works run by CPU
    ----- -----------------------
    CPU0: 7
    CPU1: 445
    CPU2: 444
    CPU3: 315
    CPU4: 226

    With my modifications:

    CPU No. of works run by CPU
    ---- -----------------------
    CPU0: 31
    CPU2: 797
    CPU3: 274
    CPU4: 86

    Test case 2:
    I have created a small module, which does following:
    - Create one work for each CPU (using queue_work_on(), so must schedule on that
    - Above work, will queue "n" works for each cpu with queue_work(). These works
    are tracked within the module and results are printed at the end.

    This gave similar results, with n ranging from 10 to 1000.

    Viresh Kumar (3):
    sched: Create sched_select_cpu() to give preferred CPU for power
    workqueue: create __flush_delayed_work to avoid duplicating code
    workqueue: Schedule work on non-idle cpu instead of current one

    arch/arm/Kconfig | 11 +++++++
    include/linux/sched.h | 11 +++++++
    kernel/sched/core.c | 88 +++++++++++++++++++++++++++++++++++++++------------
    kernel/workqueue.c | 36 ++++++++++++++-------
    4 files changed, 115 insertions(+), 31 deletions(-)


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