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From: Dietmar Eggemann <dietmar.eggemann@arm.com>
To: Qais Yousef <qais.yousef@arm.com>
Cc: Ingo Molnar <mingo@kernel.org>,
	Peter Zijlstra <peterz@infradead.org>,
	Steven Rostedt <rostedt@goodmis.org>,
	Pavan Kondeti <pkondeti@codeaurora.org>,
	Juri Lelli <juri.lelli@redhat.com>,
	Vincent Guittot <vincent.guittot@linaro.org>,
	Ben Segall <bsegall@google.com>, Mel Gorman <mgorman@suse.de>,
	linux-kernel@vger.kernel.org
Subject: Re: [PATCH v2 6/6] sched/rt: Remove unnecessary assignment in inc/dec_rt_migration
Date: Mon, 24 Feb 2020 13:03:23 +0000	[thread overview]
Message-ID: <90e4af9c-b4e3-00bf-ebe6-5d4fe6f892aa@arm.com> (raw)
In-Reply-To: <20200224123123.gbox3tcqcist7bbg@e107158-lin.cambridge.arm.com>

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:

[...]

>>> -	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 "/"

[...]

  reply	other threads:[~2020-02-24 13:03 UTC|newest]

Thread overview: 21+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-02-23 18:39 [PATCH v2 0/6] RT Capacity Awareness Fixes & Improvements Qais Yousef
2020-02-23 18:39 ` [PATCH v2 1/6] sched/rt: cpupri_find: implement fallback mechanism for !fit case Qais Yousef
2020-02-23 18:39 ` [PATCH v2 2/6] sched/rt: Re-instate old behavior in select_task_rq_rt Qais Yousef
2020-02-25 15:21   ` Dietmar Eggemann
2020-02-26 11:34     ` Qais Yousef
2020-02-23 18:39 ` [PATCH v2 3/6] sched/rt: Optimize cpupri_find on non-heterogenous systems Qais Yousef
2020-02-23 18:39 ` [PATCH v2 4/6] sched/rt: allow pulling unfitting task Qais Yousef
2020-02-23 18:40 ` [PATCH v2 5/6] sched/rt: Better manage pushing unfit tasks on wakeup Qais Yousef
2020-02-24  6:10   ` Pavan Kondeti
2020-02-24 12:11     ` Qais Yousef
2020-02-24 16:04       ` Pavan Kondeti
2020-02-24 17:41         ` Qais Yousef
2020-02-25  3:55           ` Pavan Kondeti
2020-02-26 16:02             ` Qais Yousef
2020-02-27  3:36               ` Pavan Kondeti
2020-02-27 10:29                 ` Qais Yousef
2020-02-23 18:40 ` [PATCH v2 6/6] sched/rt: Remove unnecessary assignment in inc/dec_rt_migration Qais Yousef
2020-02-23 23:16   ` Dietmar Eggemann
2020-02-24 12:31     ` Qais Yousef
2020-02-24 13:03       ` Dietmar Eggemann [this message]
2020-02-24 13:47         ` Qais Yousef

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