linux-kernel - Re: [PATCH 1/4] sched/rt: Sum number of all children tasks in hierarhy at rt_nr

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Date:	Tue, 18 Mar 2014 16:38:29 +0530
From:	Preeti Murthy <preeti.lkml@...il.com>
To:	tkhai@...dex.ru
Cc:	LKML <linux-kernel@...r.kernel.org>,
	Peter Zijlstra <peterz@...radead.org>,
	Ingo Molnar <mingo@...nel.org>,
	Preeti U Murthy <preeti@...ux.vnet.ibm.com>
Subject: Re: [PATCH 1/4] sched/rt: Sum number of all children tasks in
 hierarhy at rt_nr_running

On Sat, Mar 15, 2014 at 3:44 AM, Kirill Tkhai <tkhai@...dex.ru> wrote:
> {inc,dec}_rt_tasks used to count entities which are directly queued
> on rt_rq. If an entity was not a task (i.e., it is some queue), its
> children were not counted.

Its always the case that a task is queued right, never a sched entity?
When a task is queued, the nr_running of every rt_rq in the hierarchy
of sched entities which are parents of this task is incremented by 1.
Similar is with dequeue of a sched_entity. If the sched_entity has
just 1 task on it, then its dequeued from its parent queue and its number
decremented for every rq in the hierarchy. But you would
never dequeue a sched_entity if it has more than 1 task in it. The
granularity of enqueue and dequeue of sched_entities is one task
at a time. You can extend this to enqueue and dequeue of a sched_entity
only if it has just one task in its queue.

Regards
Preeti U Murthy


>
> There is no problem here, but now we want to count number of all tasks
> which are actually queued under the rt_rq in all the hierarhy (except
> throttled rt queues).
>
> Empty queues are not able to be queued and all of the places, which
> use rt_nr_running, just compare it with zero, so we do not break
> anything here.
>
> Signed-off-by: Kirill Tkhai <tkhai@...dex.ru>
> CC: Peter Zijlstra <peterz@...radead.org>
> CC: Ingo Molnar <mingo@...nel.org>
> ---
>  kernel/sched/rt.c |   15 +++++++++++++--
>  1 file changed, 13 insertions(+), 2 deletions(-)
>
> diff --git a/kernel/sched/rt.c b/kernel/sched/rt.c
> index d8cdf16..e4def13 100644
> --- a/kernel/sched/rt.c
> +++ b/kernel/sched/rt.c
> @@ -1045,12 +1045,23 @@ void dec_rt_group(struct sched_rt_entity *rt_se, struct rt_rq *rt_rq) {}
>  #endif /* CONFIG_RT_GROUP_SCHED */
>
>  static inline
> +unsigned int rt_se_nr_running(struct sched_rt_entity *rt_se)
> +{
> +       struct rt_rq *group_rq = group_rt_rq(rt_se);
> +
> +       if (group_rq)
> +               return group_rq->rt_nr_running;
> +       else
> +               return 1;
> +}
> +
> +static inline
>  void inc_rt_tasks(struct sched_rt_entity *rt_se, struct rt_rq *rt_rq)
>  {
>         int prio = rt_se_prio(rt_se);
>
>         WARN_ON(!rt_prio(prio));
> -       rt_rq->rt_nr_running++;
> +       rt_rq->rt_nr_running += rt_se_nr_running(rt_se);
>
>         inc_rt_prio(rt_rq, prio);
>         inc_rt_migration(rt_se, rt_rq);
> @@ -1062,7 +1073,7 @@ void dec_rt_tasks(struct sched_rt_entity *rt_se, struct rt_rq *rt_rq)
>  {
>         WARN_ON(!rt_prio(rt_se_prio(rt_se)));
>         WARN_ON(!rt_rq->rt_nr_running);
> -       rt_rq->rt_nr_running--;
> +       rt_rq->rt_nr_running -= rt_se_nr_running(rt_se);
>
>         dec_rt_prio(rt_rq, rt_se_prio(rt_se));
>         dec_rt_migration(rt_se, rt_rq);
>
>
>
>
> --
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