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Date: Tue, 15 Jul 2008 07:05:55 -0600
From: "Gregory Haskins" <ghaskins@...ell.com>
To: "Dmitry Adamushko" <dmitry.adamushko@...il.com>
Cc: "Peter Zijlstra" <a.p.zijlstra@...llo.nl>,
"Ingo Molnar" <mingo@...e.hu>,
"Steven Rostedt" <rostedt@...dmis.org>,
"Thomas Gleixner" <tglx@...utronix.de>,
"Linux Kernel" <linux-kernel@...r.kernel.org>
Subject: Re: [sched-devel, patch-rfc] rework #2 of "prioritize
non-migratable tasks over migratable ones"
>>> On Mon, Jul 14, 2008 at 10:50 AM, in message
<b647ffbd0807140750r54e5139aj7b25a28ef7ca247e@...l.gmail.com>, "Dmitry
Adamushko" <dmitry.adamushko@...il.com> wrote:
> 2008/7/1 Dmitry Adamushko <dmitry.adamushko@...il.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?
Hi Dmitry,
A brief inspection of the patch looks good. I am still not convinced we need to worry
about this condition anymore, however. The fact that we cannot guarantee that the
migratable task will start running seems that it violates *something*, even if it is not
technically called out in posix. :)
But if we are going to solve that problem, this seems like a decent way to do it.
Regards,
-Greg
>
> TIA,
>
>
>>
>> ---
>> From: Dmitry Adamushko <dmitry.adamushko@...il.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@...il.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
>>
>>
>>
--
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