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    Subject[RFC][PATCH 05/18] sched: Provide p->on_rq
    Provide a generic p->on_rq because the p->se.on_rq semantics are
    unfavourable for lockless wakeups but needed for sched_fair.

    In particular, p->on_rq is only cleared when we actually dequeue the
    task in schedule() and not on any random dequeue as done by things
    like __migrate_task() and __sched_setscheduler().

    This also allows us to remove p->se usage from !sched_fair code.

    Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
    ---
    include/linux/sched.h | 1 +
    kernel/sched.c | 36 ++++++++++++++++++------------------
    kernel/sched_debug.c | 2 +-
    kernel/sched_rt.c | 10 +++++-----
    kernel/sched_stoptask.c | 2 +-
    5 files changed, 26 insertions(+), 25 deletions(-)

    Index: linux-2.6/include/linux/sched.h
    ===================================================================
    --- linux-2.6.orig/include/linux/sched.h
    +++ linux-2.6/include/linux/sched.h
    @@ -1200,6 +1200,7 @@ struct task_struct {
    #ifdef CONFIG_SMP
    int on_cpu;
    #endif
    + int on_rq;

    int prio, static_prio, normal_prio;
    unsigned int rt_priority;
    Index: linux-2.6/kernel/sched.c
    ===================================================================
    --- linux-2.6.orig/kernel/sched.c
    +++ linux-2.6/kernel/sched.c
    @@ -1759,7 +1759,6 @@ static void enqueue_task(struct rq *rq,
    update_rq_clock(rq);
    sched_info_queued(p);
    p->sched_class->enqueue_task(rq, p, flags);
    - p->se.on_rq = 1;
    }

    static void dequeue_task(struct rq *rq, struct task_struct *p, int flags)
    @@ -1767,7 +1766,6 @@ static void dequeue_task(struct rq *rq,
    update_rq_clock(rq);
    sched_info_dequeued(p);
    p->sched_class->dequeue_task(rq, p, flags);
    - p->se.on_rq = 0;
    }

    /*
    @@ -1780,6 +1778,7 @@ static void activate_task(struct rq *rq,

    enqueue_task(rq, p, flags);
    inc_nr_running(rq);
    + p->on_rq = 1;
    }

    /*
    @@ -2070,7 +2069,7 @@ static void check_preempt_curr(struct rq
    * A queue event has occurred, and we're going to schedule. In
    * this case, we can save a useless back to back clock update.
    */
    - if (rq->curr->se.on_rq && test_tsk_need_resched(rq->curr))
    + if (rq->curr->on_rq && test_tsk_need_resched(rq->curr))
    rq->skip_clock_update = 1;
    }

    @@ -2145,7 +2144,7 @@ static bool migrate_task(struct task_str
    * If the task is not on a runqueue (and not running), then
    * the next wake-up will properly place the task.
    */
    - return p->se.on_rq || task_running(rq, p);
    + return p->on_rq || task_running(rq, p);
    }

    /*
    @@ -2205,7 +2204,7 @@ unsigned long wait_task_inactive(struct
    rq = task_rq_lock(p, &flags);
    trace_sched_wait_task(p);
    running = task_running(rq, p);
    - on_rq = p->se.on_rq;
    + on_rq = p->on_rq;
    ncsw = 0;
    if (!match_state || p->state == match_state)
    ncsw = p->nvcsw | LONG_MIN; /* sets MSB */
    @@ -2457,7 +2456,7 @@ static int try_to_wake_up(struct task_st

    cpu = task_cpu(p);

    - if (p->se.on_rq)
    + if (p->on_rq)
    goto out_running;

    orig_cpu = cpu;
    @@ -2534,7 +2533,7 @@ static void try_to_wake_up_local(struct
    if (!(p->state & TASK_NORMAL))
    return;

    - if (!p->se.on_rq)
    + if (!p->on_rq)
    activate_task(rq, p, ENQUEUE_WAKEUP);

    ttwu_post_activation(p, rq, 0);
    @@ -2571,18 +2570,20 @@ int wake_up_state(struct task_struct *p,
    */
    static void __sched_fork(struct task_struct *p)
    {
    + p->on_rq = 0;
    +
    + p->se.on_rq = 0;
    p->se.exec_start = 0;
    p->se.sum_exec_runtime = 0;
    p->se.prev_sum_exec_runtime = 0;
    p->se.nr_migrations = 0;
    + INIT_LIST_HEAD(&p->se.group_node);

    #ifdef CONFIG_SCHEDSTATS
    memset(&p->se.statistics, 0, sizeof(p->se.statistics));
    #endif

    INIT_LIST_HEAD(&p->rt.run_list);
    - p->se.on_rq = 0;
    - INIT_LIST_HEAD(&p->se.group_node);

    #ifdef CONFIG_PREEMPT_NOTIFIERS
    INIT_HLIST_HEAD(&p->preempt_notifiers);
    @@ -3904,7 +3905,7 @@ static inline void schedule_debug(struct

    static void put_prev_task(struct rq *rq, struct task_struct *prev)
    {
    - if (prev->se.on_rq)
    + if (prev->on_rq)
    update_rq_clock(rq);
    prev->sched_class->put_prev_task(rq, prev);
    }
    @@ -3983,6 +3984,7 @@ asmlinkage void __sched schedule(void)
    try_to_wake_up_local(to_wakeup);
    }
    deactivate_task(rq, prev, DEQUEUE_SLEEP);
    + prev->on_rq = 0;
    }
    switch_count = &prev->nvcsw;
    }
    @@ -4546,7 +4548,7 @@ void rt_mutex_setprio(struct task_struct
    trace_sched_pi_setprio(p, prio);
    oldprio = p->prio;
    prev_class = p->sched_class;
    - on_rq = p->se.on_rq;
    + on_rq = p->on_rq;
    running = task_current(rq, p);
    if (on_rq)
    dequeue_task(rq, p, 0);
    @@ -4595,7 +4597,7 @@ void set_user_nice(struct task_struct *p
    p->static_prio = NICE_TO_PRIO(nice);
    goto out_unlock;
    }
    - on_rq = p->se.on_rq;
    + on_rq = p->on_rq;
    if (on_rq)
    dequeue_task(rq, p, 0);

    @@ -4729,8 +4731,6 @@ static struct task_struct *find_process_
    static void
    __setscheduler(struct rq *rq, struct task_struct *p, int policy, int prio)
    {
    - BUG_ON(p->se.on_rq);
    -
    p->policy = policy;
    p->rt_priority = prio;
    p->normal_prio = normal_prio(p);
    @@ -4878,7 +4878,7 @@ static int __sched_setscheduler(struct t
    raw_spin_unlock_irqrestore(&p->pi_lock, flags);
    goto recheck;
    }
    - on_rq = p->se.on_rq;
    + on_rq = p->on_rq;
    running = task_current(rq, p);
    if (on_rq)
    deactivate_task(rq, p, 0);
    @@ -5737,7 +5737,7 @@ static int __migrate_task(struct task_st
    * If we're not on a rq, the next wake-up will ensure we're
    * placed properly.
    */
    - if (p->se.on_rq) {
    + if (p->on_rq) {
    deactivate_task(rq_src, p, 0);
    set_task_cpu(p, dest_cpu);
    activate_task(rq_dest, p, 0);
    @@ -8106,7 +8106,7 @@ static void normalize_task(struct rq *rq
    {
    int on_rq;

    - on_rq = p->se.on_rq;
    + on_rq = p->on_rq;
    if (on_rq)
    deactivate_task(rq, p, 0);
    __setscheduler(rq, p, SCHED_NORMAL, 0);
    @@ -8449,7 +8449,7 @@ void sched_move_task(struct task_struct
    rq = task_rq_lock(tsk, &flags);

    running = task_current(rq, tsk);
    - on_rq = tsk->se.on_rq;
    + on_rq = tsk->on_rq;

    if (on_rq)
    dequeue_task(rq, tsk, 0);
    Index: linux-2.6/kernel/sched_debug.c
    ===================================================================
    --- linux-2.6.orig/kernel/sched_debug.c
    +++ linux-2.6/kernel/sched_debug.c
    @@ -127,7 +127,7 @@ static void print_rq(struct seq_file *m,
    read_lock_irqsave(&tasklist_lock, flags);

    do_each_thread(g, p) {
    - if (!p->se.on_rq || task_cpu(p) != rq_cpu)
    + if (!p->on_rq || task_cpu(p) != rq_cpu)
    continue;

    print_task(m, rq, p);
    Index: linux-2.6/kernel/sched_rt.c
    ===================================================================
    --- linux-2.6.orig/kernel/sched_rt.c
    +++ linux-2.6/kernel/sched_rt.c
    @@ -1132,7 +1132,7 @@ static void put_prev_task_rt(struct rq *
    * The previous task needs to be made eligible for pushing
    * if it is still active
    */
    - if (p->se.on_rq && p->rt.nr_cpus_allowed > 1)
    + if (p->on_rq && p->rt.nr_cpus_allowed > 1)
    enqueue_pushable_task(rq, p);
    }

    @@ -1283,7 +1283,7 @@ static struct rq *find_lock_lowest_rq(st
    !cpumask_test_cpu(lowest_rq->cpu,
    &task->cpus_allowed) ||
    task_running(rq, task) ||
    - !task->se.on_rq)) {
    + !task->on_rq)) {

    raw_spin_unlock(&lowest_rq->lock);
    lowest_rq = NULL;
    @@ -1317,7 +1317,7 @@ static struct task_struct *pick_next_pus
    BUG_ON(task_current(rq, p));
    BUG_ON(p->rt.nr_cpus_allowed <= 1);

    - BUG_ON(!p->se.on_rq);
    + BUG_ON(!p->on_rq);
    BUG_ON(!rt_task(p));

    return p;
    @@ -1463,7 +1463,7 @@ static int pull_rt_task(struct rq *this_
    */
    if (p && (p->prio < this_rq->rt.highest_prio.curr)) {
    WARN_ON(p == src_rq->curr);
    - WARN_ON(!p->se.on_rq);
    + WARN_ON(!p->on_rq);

    /*
    * There's a chance that p is higher in priority
    @@ -1534,7 +1534,7 @@ static void set_cpus_allowed_rt(struct t
    * Update the migration status of the RQ if we have an RT task
    * which is running AND changing its weight value.
    */
    - if (p->se.on_rq && (weight != p->rt.nr_cpus_allowed)) {
    + if (p->on_rq && (weight != p->rt.nr_cpus_allowed)) {
    struct rq *rq = task_rq(p);

    if (!task_current(rq, p)) {
    Index: linux-2.6/kernel/sched_stoptask.c
    ===================================================================
    --- linux-2.6.orig/kernel/sched_stoptask.c
    +++ linux-2.6/kernel/sched_stoptask.c
    @@ -26,7 +26,7 @@ static struct task_struct *pick_next_tas
    {
    struct task_struct *stop = rq->stop;

    - if (stop && stop->se.on_rq)
    + if (stop && stop->on_rq)
    return stop;

    return NULL;



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