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    SubjectRe: [PATCH v3 4/6] sched/rt: fast switch to maximum frequency when RT tasks are scheduled
    Hi,

    On 30/11/17 11:47, Patrick Bellasi wrote:
    > Currently schedutil updates are triggered for the RT class using a single
    > call place, which is part of the rt::update_curr_rt() used in:
    >
    > - dequeue_task_rt:
    > but it does not make sense to set the schedutil's SCHED_CPUFREQ_RT in
    > case the next task should not be an RT one
    >
    > - put_prev_task_rt:
    > likewise, we set the SCHED_CPUFREQ_RT flag without knowing if required
    > by the next task
    >
    > - pick_next_task_rt:
    > likewise, the schedutil's SCHED_CPUFREQ_RT is set in case the prev task
    > was RT, while we don't yet know if the next will be RT
    >
    > - task_tick_rt:
    > that's the only really useful call, which can ramp up the frequency in
    > case a RT task started its execution without a chance to order a
    > frequency switch (e.g. because of the schedutil ratelimit)
    >
    > Apart from the last call in task_tick_rt, the others are at least useless.
    > Thus, although being a simple solution, not all the call sites of that
    > update_curr_rt() are interesting to trigger a frequency switch as well as
    > some of the most interesting points are not covered by that call.
    > For example, a task set to RT has to wait the next tick to get the
    > frequency boost.
    >
    > This patch fixes these issues by placing explicitly the schedutils
    > update calls in the only sensible places, which are:
    > - when an RT task wakes up and it's enqueued in a CPU
    > - when we actually pick a RT task for execution
    > - at each tick time
    > - when a task is set to be RT
    >
    > Signed-off-by: Patrick Bellasi <patrick.bellasi@arm.com>
    > Reviewed-by: Dietmar Eggemann <dietmar.eggemann@arm.com>

    Reviewed-by: Juri Lelli <juri.lelli@redhat.com>

    Best,

    Juri

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