Re: [PATCH RFC v5 3/4] Revert "sched/rt: Substract number of tasks of throttled queues from rq->nr_running"

[Qais Yousef <qyousef@layalina.io>]

On 11/3/26 18:51, Kayra Cizmeci wrote:

> So, as I was saying above I gave this a run. Did some tests:
> 
> In my base a RT task can only get a CPU's %95.5, with the series %99.9.
> Even when rt_throttled is 1, task doesn't stop running. I opened
> CONFIG_RT_GROUP_SCHED and set cpu.rt_runtime_us to 950000. cgroup v1.
> 
> 
> And AFAICT from the code and my tests, nr_running is handled
> differently/wrong with this patch.
> 
> When there is a RT group while throttling is enabled, with 2 tasks when
> the group throttles nr_running should be 0. Since, there is nothing to
> run. (If the group is alone in the rq tho :>) But with the patch series,
> it stays 2. I think it's because dec_rt_tasks() does not call
> sub_nr_running() in the group_rt_rq() case of se.
> 
> 
> Or am I missing something :-)?

This is an RFC as I was looking for potential historical context why it had to
be done this way. I did call out in the cover letter that I am not sure about
the implementation of inc/dec_rt_tasks() and was looking for advise too.

I might have just missed that we have rt_task_is_entity(), does things get
better with the below? Otherwise I'll just need to find the time to figure out
the code and test it properly. Thanks!

--->8---

diff --git a/kernel/sched/rt.c b/kernel/sched/rt.c
index 96d37a1ccc2a8..520273086134d 100644
--- a/kernel/sched/rt.c
+++ b/kernel/sched/rt.c
@@ -1132,7 +1132,7 @@ void inc_rt_tasks(struct sched_rt_entity *rt_se, struct
rt_rq *rt_rq)
        inc_rt_prio(rt_rq, prio);
        inc_rt_group(rt_se, rt_rq);

-       if (!group_rt_rq(rt_se)) {
+       if (rt_entity_is_task(rt_se)) {
                struct rq *rq = rq_of_rt_rq(rt_rq);

                add_nr_running(rq, 1);
@@ -1151,7 +1151,7 @@ void dec_rt_tasks(struct sched_rt_entity *rt_se, struct
rt_rq *rt_rq)
        dec_rt_prio(rt_rq, rt_se_prio(rt_se));
        dec_rt_group(rt_se, rt_rq);

-       if (!group_rt_rq(rt_se)) {
+       if (rt_entity_is_task(rt_se)) {
                struct rq *rq = rq_of_rt_rq(rt_rq);

                sub_nr_running(rq, 1);