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    Subject[PATCH 3/3] sched: add avg-overlap support to RT tasks
    Date
    We have the notion of tracking process-coupling (a.k.a. buddy-wake) via
    the p->se.last_wake / p->se.avg_overlap facilities, but it is only used
    for cfs to cfs interactions. There is no reason why an rt to cfs
    interaction cannot share in establishing a relationhip in a similar
    manner.

    Because PREEMPT_RT runs many kernel threads as FIFO priority, we often
    times have heavy interaction between RT threads waking CFS applications.
    This patch offers a substantial boost (50-60%+) in perfomance under those
    circumstances.

    Signed-off-by: Gregory Haskins <ghaskins@novell.com>
    ---

    kernel/sched.c | 14 ++++++++++++++
    kernel/sched_fair.c | 21 ++-------------------
    2 files changed, 16 insertions(+), 19 deletions(-)

    diff --git a/kernel/sched.c b/kernel/sched.c
    index 0b9f90e..af9a68b 100644
    --- a/kernel/sched.c
    +++ b/kernel/sched.c
    @@ -1544,6 +1544,12 @@ static void set_load_weight(struct task_struct *p)
    p->se.load.inv_weight = prio_to_wmult[p->static_prio - MAX_RT_PRIO];
    }

    +static void update_avg(u64 *avg, u64 sample)
    +{
    + s64 diff = sample - *avg;
    + *avg += diff >> 3;
    +}
    +
    static void enqueue_task(struct rq *rq, struct task_struct *p, int wakeup)
    {
    sched_info_queued(p);
    @@ -1553,6 +1559,12 @@ static void enqueue_task(struct rq *rq, struct task_struct *p, int wakeup)

    static void dequeue_task(struct rq *rq, struct task_struct *p, int sleep)
    {
    + if (sleep && p->se.last_wakeup) {
    + update_avg(&p->se.avg_overlap,
    + p->se.sum_exec_runtime - p->se.last_wakeup);
    + p->se.last_wakeup = 0;
    + }
    +
    p->sched_class->dequeue_task(rq, p, sleep);
    p->se.on_rq = 0;
    }
    @@ -2157,6 +2169,8 @@ out_running:
    p->sched_class->task_wake_up(rq, p);
    #endif
    out:
    + current->se.last_wakeup = current->se.sum_exec_runtime;
    +
    task_rq_unlock(rq, &flags);

    return success;
    diff --git a/kernel/sched_fair.c b/kernel/sched_fair.c
    index 8e77d67..3c06027 100644
    --- a/kernel/sched_fair.c
    +++ b/kernel/sched_fair.c
    @@ -639,21 +639,6 @@ enqueue_entity(struct cfs_rq *cfs_rq, struct sched_entity *se, int wakeup)
    __enqueue_entity(cfs_rq, se);
    }

    -static void update_avg(u64 *avg, u64 sample)
    -{
    - s64 diff = sample - *avg;
    - *avg += diff >> 3;
    -}
    -
    -static void update_avg_stats(struct cfs_rq *cfs_rq, struct sched_entity *se)
    -{
    - if (!se->last_wakeup)
    - return;
    -
    - update_avg(&se->avg_overlap, se->sum_exec_runtime - se->last_wakeup);
    - se->last_wakeup = 0;
    -}
    -
    static void
    dequeue_entity(struct cfs_rq *cfs_rq, struct sched_entity *se, int sleep)
    {
    @@ -664,7 +649,6 @@ dequeue_entity(struct cfs_rq *cfs_rq, struct sched_entity *se, int sleep)

    update_stats_dequeue(cfs_rq, se);
    if (sleep) {
    - update_avg_stats(cfs_rq, se);
    #ifdef CONFIG_SCHEDSTATS
    if (entity_is_task(se)) {
    struct task_struct *tsk = task_of(se);
    @@ -1016,9 +1000,9 @@ wake_affine(struct rq *rq, struct sched_domain *this_sd, struct rq *this_rq,
    * a reasonable amount of time then attract this newly
    * woken task:
    */
    - if (sync && balanced && curr->sched_class == &fair_sched_class) {
    + if (sync && balanced) {
    if (curr->se.avg_overlap < sysctl_sched_migration_cost &&
    - p->se.avg_overlap < sysctl_sched_migration_cost)
    + p->se.avg_overlap < sysctl_sched_migration_cost)
    return 1;
    }

    @@ -1177,7 +1161,6 @@ static void check_preempt_wakeup(struct rq *rq, struct task_struct *p)
    return;
    }

    - se->last_wakeup = se->sum_exec_runtime;
    if (unlikely(se == pse))
    return;



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