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    Subject[patch 13/18] sched: migrate throttled tasks on HOTPLUG
    Throttled tasks are invisisble to cpu-offline since they are not eligible for
    selection by pick_next_task(). The regular 'escape' path for a thread that is
    blocked at offline is via ttwu->select_task_rq, however this will not handle a
    throttled group since there are no individual thread wakeups on an unthrottle.

    Resolve this by unthrottling offline cpus so that threads can be migrated.

    Signed-off-by: Paul Turner <pjt@google.com>
    Reviewed-by: Hidetoshi Seto <seto.hidetoshi@jp.fujitsu.com>

    ---
    kernel/sched.c | 27 +++++++++++++++++++++++++++
    1 file changed, 27 insertions(+)

    Index: tip/kernel/sched.c
    ===================================================================
    --- tip.orig/kernel/sched.c
    +++ tip/kernel/sched.c
    @@ -6271,6 +6271,30 @@ static void calc_global_load_remove(stru
    rq->calc_load_active = 0;
    }

    +#ifdef CONFIG_CFS_BANDWIDTH
    +static void unthrottle_offline_cfs_rqs(struct rq *rq)
    +{
    + struct cfs_rq *cfs_rq;
    +
    + for_each_leaf_cfs_rq(rq, cfs_rq) {
    + struct cfs_bandwidth *cfs_b = tg_cfs_bandwidth(cfs_rq->tg);
    +
    + if (!cfs_rq->runtime_enabled)
    + continue;
    +
    + /*
    + * clock_task is not advancing so we just need to make sure
    + * there's some valid quota amount
    + */
    + cfs_rq->runtime_remaining = cfs_b->quota;
    + if (cfs_rq_throttled(cfs_rq))
    + unthrottle_cfs_rq(cfs_rq);
    + }
    +}
    +#else
    +static void unthrottle_offline_cfs_rqs(struct rq *rq) {}
    +#endif
    +
    /*
    * Migrate all tasks from the rq, sleeping tasks will be migrated by
    * try_to_wake_up()->select_task_rq().
    @@ -6296,6 +6320,9 @@ static void migrate_tasks(unsigned int d
    */
    rq->stop = NULL;

    + /* Ensure any throttled groups are reachable by pick_next_task */
    + unthrottle_offline_cfs_rqs(rq);
    +
    for ( ; ; ) {
    /*
    * There's this thread running, bail when that's the only



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