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    Subject[RFC][PATCH 13/13] sched/fair: Add trivial fair server


    Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
    ---
    kernel/sched/core.c | 6 +++++-
    kernel/sched/deadline.c | 2 ++
    kernel/sched/fair.c | 29 +++++++++++++++++++++++++++++
    kernel/sched/sched.h | 6 +++++-
    4 files changed, 41 insertions(+), 2 deletions(-)

    --- a/kernel/sched/core.c
    +++ b/kernel/sched/core.c
    @@ -6501,6 +6504,7 @@ void __init sched_init(void)
    #endif /* CONFIG_SMP */
    hrtick_rq_init(rq);
    atomic_set(&rq->nr_iowait, 0);
    + fair_server_init(rq);
    }

    set_load_weight(&init_task, false);
    --- a/kernel/sched/fair.c
    +++ b/kernel/sched/fair.c
    @@ -5239,6 +5239,9 @@ enqueue_task_fair(struct rq *rq, struct
    */
    util_est_enqueue(&rq->cfs, p);

    + if (!rq->cfs.h_nr_running)
    + dl_server_start(&rq->fair_server);
    +
    /*
    * If in_iowait is set, the code below may not trigger any cpufreq
    * utilization updates, so do it here explicitly with the IOWAIT flag
    @@ -5374,6 +5377,9 @@ static void dequeue_task_fair(struct rq
    if (!se)
    sub_nr_running(rq, 1);

    + if (!rq->cfs.h_nr_running)
    + dl_server_stop(&rq->fair_server);
    +
    util_est_dequeue(&rq->cfs, p, task_sleep);
    hrtick_update(rq);
    }
    @@ -6903,6 +6909,29 @@ done: __maybe_unused;
    return NULL;
    }

    +static bool fair_server_has_tasks(struct sched_dl_entity *dl_se)
    +{
    + return !!dl_se->rq->cfs.nr_running;
    +}
    +
    +static struct task_struct *fair_server_pick(struct sched_dl_entity *dl_se)
    +{
    + return pick_next_task_fair(dl_se->rq, NULL, NULL);
    +}
    +
    +void fair_server_init(struct rq *rq)
    +{
    + struct sched_dl_entity *dl_se = &rq->fair_server;
    +
    + init_dl_entity(dl_se);
    +
    + dl_se->dl_runtime = TICK_NSEC;
    + dl_se->dl_deadline = 20 * TICK_NSEC;
    + dl_se->dl_period = 20 * TICK_NSEC;
    +
    + dl_server_init(dl_se, rq, fair_server_has_tasks, fair_server_pick);
    +}
    +
    /*
    * Account for a descheduled task:
    */
    --- a/kernel/sched/sched.h
    +++ b/kernel/sched/sched.h
    @@ -345,6 +345,8 @@ extern void dl_server_init(struct sched_
    dl_server_has_tasks_f has_tasks,
    dl_server_pick_f pick);

    +extern void fair_server_init(struct rq *);
    +
    #ifdef CONFIG_CGROUP_SCHED

    #include <linux/cgroup.h>
    @@ -905,6 +907,8 @@ struct rq {
    struct rt_rq rt;
    struct dl_rq dl;

    + struct sched_dl_entity fair_server;
    +
    #ifdef CONFIG_FAIR_GROUP_SCHED
    /* list of leaf cfs_rq on this CPU: */
    struct list_head leaf_cfs_rq_list;
    @@ -968,7 +972,7 @@ struct rq {

    /* This is used to determine avg_idle's max value */
    u64 max_idle_balance_cost;
    -#endif
    +#endif /* CONFIG_SMP */

    #ifdef CONFIG_IRQ_TIME_ACCOUNTING
    u64 prev_irq_time;

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