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    SubjectRe: [sched-devel, patch-rfc] rework #2 of "prioritize non-migratable tasks over migratable ones"
    2008/7/1 Dmitry Adamushko <dmitry.adamushko@gmail.com>:
    >
    > Finally, this new version compiles and boots (applied a minor compilation fix).
    > Functionality is not yet fully tested though.
    >
    > It's on top of today's tip tree.
    >
    > Any objections to this approach?

    [ ping ]

    Gregory or anyone else, any feedback on this one?

    TIA,


    >
    > ---
    > From: Dmitry Adamushko <dmitry.adamushko@gmail.com>
    > Subject: prioritize non-migratable tasks over migratable ones in a generic way
    >
    > (1) handle in a generic way all cases when a newly woken-up task is
    > not migratable (not just a corner case when "rt_se->nr_cpus_allowed ==
    > 1")
    >
    > (2) if current is to be preempted, then make sure "p" will be picked
    > up by pick_next_task_rt().
    > i.e. move task's group at the head of its list as well.
    >
    > currently, it's not a case for the group-scheduling case as described
    > here: http://www.ussg.iu.edu/hypermail/linux/kernel/0807.0/0134.html
    >
    >
    > Signed-off-by: Dmitry Adamushko <dmitry.adamushko@gmail.com>
    >
    > ---
    > diff --git a/kernel/sched_rt.c b/kernel/sched_rt.c
    > index 7c96147..7bc73e8 100644
    > --- a/kernel/sched_rt.c
    > +++ b/kernel/sched_rt.c
    > @@ -599,11 +599,7 @@ static void __enqueue_rt_entity(struct sched_rt_entity *rt_se)
    > if (group_rq && (rt_rq_throttled(group_rq) || !group_rq->rt_nr_running))
    > return;
    >
    > - if (rt_se->nr_cpus_allowed == 1)
    > - list_add(&rt_se->run_list, queue);
    > - else
    > - list_add_tail(&rt_se->run_list, queue);
    > -
    > + list_add_tail(&rt_se->run_list, queue);
    > __set_bit(rt_se_prio(rt_se), array->bitmap);
    >
    > inc_rt_tasks(rt_se, rt_rq);
    > @@ -689,31 +685,33 @@ static void dequeue_task_rt(struct rq *rq, struct task_struct *p, int sleep)
    > * followed by enqueue.
    > */
    > static
    > -void requeue_rt_entity(struct rt_rq *rt_rq, struct sched_rt_entity *rt_se)
    > +void requeue_rt_entity(struct rt_rq *rt_rq, struct sched_rt_entity *rt_se, int head)
    > {
    > - struct rt_prio_array *array = &rt_rq->active;
    > -
    > if (on_rt_rq(rt_se)) {
    > - list_del_init(&rt_se->run_list);
    > - list_add_tail(&rt_se->run_list,
    > - array->queue + rt_se_prio(rt_se));
    > + struct rt_prio_array *array = &rt_rq->active;
    > + struct list_head *queue = array->queue + rt_se_prio(rt_se);
    > +
    > + if (head)
    > + list_move(&rt_se->run_list, queue);
    > + else
    > + list_move_tail(&rt_se->run_list, queue);
    > }
    > }
    >
    > -static void requeue_task_rt(struct rq *rq, struct task_struct *p)
    > +static void requeue_task_rt(struct rq *rq, struct task_struct *p, int head)
    > {
    > struct sched_rt_entity *rt_se = &p->rt;
    > struct rt_rq *rt_rq;
    >
    > for_each_sched_rt_entity(rt_se) {
    > rt_rq = rt_rq_of_se(rt_se);
    > - requeue_rt_entity(rt_rq, rt_se);
    > + requeue_rt_entity(rt_rq, rt_se, head);
    > }
    > }
    >
    > static void yield_task_rt(struct rq *rq)
    > {
    > - requeue_task_rt(rq, rq->curr);
    > + requeue_task_rt(rq, rq->curr, 0);
    > }
    >
    > #ifdef CONFIG_SMP
    > @@ -753,6 +751,30 @@ static int select_task_rq_rt(struct task_struct *p, int sync)
    > */
    > return task_cpu(p);
    > }
    > +
    > +static void check_preempt_equal_prio(struct rq *rq, struct task_struct *p)
    > +{
    > + cpumask_t mask;
    > +
    > + if (rq->curr->rt.nr_cpus_allowed == 1)
    > + return;
    > +
    > + if (p->rt.nr_cpus_allowed != 1
    > + && cpupri_find(&rq->rd->cpupri, p, &mask))
    > + return;
    > +
    > + if (!cpupri_find(&rq->rd->cpupri, rq->curr, &mask))
    > + return;
    > +
    > + /*
    > + * There appears to be other cpus that can accept
    > + * current and none to run 'p', so lets reschedule
    > + * to try and push current away:
    > + */
    > + requeue_task_rt(rq, p, 1);
    > + resched_task(rq->curr);
    > +}
    > +
    > #endif /* CONFIG_SMP */
    >
    > /*
    > @@ -778,18 +800,8 @@ static void check_preempt_curr_rt(struct rq *rq, struct task_struct *p)
    > * to move current somewhere else, making room for our non-migratable
    > * task.
    > */
    > - if((p->prio == rq->curr->prio)
    > - && p->rt.nr_cpus_allowed == 1
    > - && rq->curr->rt.nr_cpus_allowed != 1) {
    > - cpumask_t mask;
    > -
    > - if (cpupri_find(&rq->rd->cpupri, rq->curr, &mask))
    > - /*
    > - * There appears to be other cpus that can accept
    > - * current, so lets reschedule to try and push it away
    > - */
    > - resched_task(rq->curr);
    > - }
    > + if (p->prio == rq->curr->prio && !need_resched())
    > + check_preempt_equal_prio(rq, p);
    > #endif
    > }
    >
    > @@ -1415,7 +1427,7 @@ static void task_tick_rt(struct rq *rq, struct task_struct *p, int queued)
    > * on the queue:
    > */
    > if (p->rt.run_list.prev != p->rt.run_list.next) {
    > - requeue_task_rt(rq, p);
    > + requeue_task_rt(rq, p, 0);
    > set_tsk_need_resched(p);
    > }
    > }
    >
    > ---
    >
    >
    > --Dmitry
    >
    >
    >

    --
    Best regards,
    Dmitry Adamushko


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