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    SubjectRe: [PATCH v7 0/8] Tunable sched_mc_power_savings=n
    * Mike Galbraith <> [2009-01-07 09:59:15]:

    > I have a couple questions if you don't mind.
    > In wake_idle() there's an odd looking check for kthreads. Why does it
    > matter if a kbuild task wakes kernel or userland helper thread?

    Only user space tasks/threads should be biased at wakeup and
    consolidated for the following reasons:

    * kernel threads generally perform housekeeping tasks and its rate of
    execution and cpu utilisation is far less than that of user task in
    an under utilised system.
    * Biasing at wakeup help consolidate bursty user space tasks. Long
    running user space tasks will be consolidated by load balancer.
    kthreads are not bursty, they are generally very short running.

    > I also don't see why sched_mc overrides domain tunings. You can turn
    > NEWIDLE off and sched_mc remains as set, so it's a one-way override. If
    > NEWIDLE is a requirement for sched_mc > 0, it seems only logical to set
    > sched_mc to 0 if the user explicitly disables NEWIDLE.

    SD_BALANCE_NEWIDLE is required for sched_mc=2 and power savings while
    not mandated for sched_mc=0. We can remove NEWIDLE balance at
    sched_mc=0 if that helps baseline performance. Ingo had identified
    that removing NEWIDLE balance help performance in certain benchmarks.

    I do not get what you have mentioned by NEWIDLE off? Is there
    a separate user space control to independently set or reset
    SD_BALANCE_NEWIDLE at a give sched_domain level?

    Thanks for the detailed review.


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