Messages in this thread | | | Subject | Re: [PATCH v2 6/6] sched/rt: Remove unnecessary assignment in inc/dec_rt_migration | From | Dietmar Eggemann <> | Date | Mon, 24 Feb 2020 13:03:23 +0000 |
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On 24.02.20 12:31, Qais Yousef wrote: > On 02/24/20 00:16, Dietmar Eggemann wrote: >> On 23.02.20 19:40, Qais Yousef wrote:
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>>> - rt_rq = &rq_of_rt_rq(rt_rq)->rt; >> >> IMHO, this is here to get the root rt_rq from any rt_rq (task_groups). >> Looks like that e.g rt_nr_total is only maintained on root rt_rq's. >> >> Similar to CFS' &rq_of(cfs_rq)->cfs (cfs_rq_util_change()) to get root >> cfs_rq. >> >> Not sure where CONFIG_RT_GROUP_SCHED=y is used but it's part of the rt >> class implementation. > > Ah I see. That was obvious.. How about the below comment? > > This code is executed only if rt_entity_is_task(), I don't think this grantees > that the rt_rq isn't for a group?
No, an rt task can run in this taskgroup (e.g. "/tg/tg1"), i.e. in tg1->rt_rq[cpu].
The taskgroup skeleton rt_se of e.g. "/tg/tg1/tg11" would also run in tg1->rt_rq[cpu] but for those rt_se's we bail out of [inc/dec]_rt_migration.
> > I need to go and unravel the layers maybe. > > Thanks! > > -- > Qais Yousef > > -->8-- > > diff --git a/kernel/sched/rt.c b/kernel/sched/rt.c > index b35e49cdafcc..f929867215c4 100644 > --- a/kernel/sched/rt.c > +++ b/kernel/sched/rt.c > @@ -343,6 +343,8 @@ static void inc_rt_migration(struct sched_rt_entity *rt_se, struct rt_rq *rt_rq) > return; > > p = rt_task_of(rt_se); > + > + /* get the root rt_rq if this is the rt_rq of a group */
Not sure if a comment like this will help since:
(a) the definition of rq_of_rt_rq() for the !CONFIG_RT_GROUP_SCHED case
(b) rt_rq might already be the root rt_rq in case the task runs in "/"
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