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    SubjectRe: [patch 2/12] sched: remove avg_wakeup
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    sched: remove avg_wakeup.

    Testing the load which led to this heuristic (nfs4 kbuild) shows that it has
    outlived it's usefullness. With intervening load balancing changes, I cannot
    see any difference with/without, so recover there fastpath cycles.

    Signed-off-by: Mike Galbraith <efault@gmx.de>
    Cc: Ingo Molnar <mingo@elte.hu>
    Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
    LKML-Reference: <new-submission>

    ---
    include/linux/sched.h | 3 ---
    kernel/sched.c | 26 ++++----------------------
    kernel/sched_debug.c | 1 -
    kernel/sched_fair.c | 31 -------------------------------
    kernel/sched_features.h | 6 ------
    5 files changed, 4 insertions(+), 63 deletions(-)

    Index: linux-2.6/include/linux/sched.h
    ===================================================================
    --- linux-2.6.orig/include/linux/sched.h
    +++ linux-2.6/include/linux/sched.h
    @@ -1105,9 +1105,6 @@ struct sched_entity {

    u64 nr_migrations;

    - u64 start_runtime;
    - u64 avg_wakeup;
    -
    #ifdef CONFIG_SCHEDSTATS
    u64 wait_start;
    u64 wait_max;
    Index: linux-2.6/kernel/sched.c
    ===================================================================
    --- linux-2.6.orig/kernel/sched.c
    +++ linux-2.6/kernel/sched.c
    @@ -1880,9 +1880,6 @@ static void update_avg(u64 *avg, u64 sam
    static void
    enqueue_task(struct rq *rq, struct task_struct *p, int wakeup, bool head)
    {
    - if (wakeup)
    - p->se.start_runtime = p->se.sum_exec_runtime;
    -
    sched_info_queued(p);
    p->sched_class->enqueue_task(rq, p, wakeup, head);
    p->se.on_rq = 1;
    @@ -1890,17 +1887,11 @@ enqueue_task(struct rq *rq, struct task_

    static void dequeue_task(struct rq *rq, struct task_struct *p, int sleep)
    {
    - if (sleep) {
    - if (p->se.last_wakeup) {
    - update_avg(&p->se.avg_overlap,
    - p->se.sum_exec_runtime - p->se.last_wakeup);
    - p->se.last_wakeup = 0;
    - } else {
    - update_avg(&p->se.avg_wakeup,
    - sysctl_sched_wakeup_granularity);
    - }
    + 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;
    }
    -
    sched_info_dequeued(p);
    p->sched_class->dequeue_task(rq, p, sleep);
    p->se.on_rq = 0;
    @@ -2466,13 +2457,6 @@ out_activate:
    */
    if (!in_interrupt()) {
    struct sched_entity *se = &current->se;
    - u64 sample = se->sum_exec_runtime;
    -
    - if (se->last_wakeup)
    - sample -= se->last_wakeup;
    - else
    - sample -= se->start_runtime;
    - update_avg(&se->avg_wakeup, sample);

    se->last_wakeup = se->sum_exec_runtime;
    }
    @@ -2540,8 +2524,6 @@ static void __sched_fork(struct task_str
    p->se.nr_migrations = 0;
    p->se.last_wakeup = 0;
    p->se.avg_overlap = 0;
    - p->se.start_runtime = 0;
    - p->se.avg_wakeup = sysctl_sched_wakeup_granularity;

    #ifdef CONFIG_SCHEDSTATS
    p->se.wait_start = 0;
    Index: linux-2.6/kernel/sched_debug.c
    ===================================================================
    --- linux-2.6.orig/kernel/sched_debug.c
    +++ linux-2.6/kernel/sched_debug.c
    @@ -408,7 +408,6 @@ void proc_sched_show_task(struct task_st
    PN(se.vruntime);
    PN(se.sum_exec_runtime);
    PN(se.avg_overlap);
    - PN(se.avg_wakeup);

    nr_switches = p->nvcsw + p->nivcsw;

    Index: linux-2.6/kernel/sched_fair.c
    ===================================================================
    --- linux-2.6.orig/kernel/sched_fair.c
    +++ linux-2.6/kernel/sched_fair.c
    @@ -1591,42 +1591,11 @@ static int select_task_rq_fair(struct ta
    }
    #endif /* CONFIG_SMP */

    -/*
    - * Adaptive granularity
    - *
    - * se->avg_wakeup gives the average time a task runs until it does a wakeup,
    - * with the limit of wakeup_gran -- when it never does a wakeup.
    - *
    - * So the smaller avg_wakeup is the faster we want this task to preempt,
    - * but we don't want to treat the preemptee unfairly and therefore allow it
    - * to run for at least the amount of time we'd like to run.
    - *
    - * NOTE: we use 2*avg_wakeup to increase the probability of actually doing one
    - *
    - * NOTE: we use *nr_running to scale with load, this nicely matches the
    - * degrading latency on load.
    - */
    -static unsigned long
    -adaptive_gran(struct sched_entity *curr, struct sched_entity *se)
    -{
    - u64 this_run = curr->sum_exec_runtime - curr->prev_sum_exec_runtime;
    - u64 expected_wakeup = 2*se->avg_wakeup * cfs_rq_of(se)->nr_running;
    - u64 gran = 0;
    -
    - if (this_run < expected_wakeup)
    - gran = expected_wakeup - this_run;
    -
    - return min_t(s64, gran, sysctl_sched_wakeup_granularity);
    -}
    -
    static unsigned long
    wakeup_gran(struct sched_entity *curr, struct sched_entity *se)
    {
    unsigned long gran = sysctl_sched_wakeup_granularity;

    - if (cfs_rq_of(curr)->curr && sched_feat(ADAPTIVE_GRAN))
    - gran = adaptive_gran(curr, se);
    -
    /*
    * Since its curr running now, convert the gran from real-time
    * to virtual-time in his units.
    Index: linux-2.6/kernel/sched_features.h
    ===================================================================
    --- linux-2.6.orig/kernel/sched_features.h
    +++ linux-2.6/kernel/sched_features.h
    @@ -31,12 +31,6 @@ SCHED_FEAT(START_DEBIT, 1)
    SCHED_FEAT(WAKEUP_PREEMPT, 1)

    /*
    - * Compute wakeup_gran based on task behaviour, clipped to
    - * [0, sched_wakeup_gran_ns]
    - */
    -SCHED_FEAT(ADAPTIVE_GRAN, 1)
    -
    -/*
    * When converting the wakeup granularity to virtual time, do it such
    * that heavier tasks preempting a lighter task have an edge.
    */



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