linux-kernel - Re: [PATCH 1/2] sched/deadline: add per rq tracking of admitted bandwidth

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Date:	Thu, 11 Feb 2016 13:22:54 +0100
From:	luca abeni <luca.abeni@...tn.it>
To:	Juri Lelli <juri.lelli@....com>
Cc:	Steven Rostedt <rostedt@...dmis.org>, linux-kernel@...r.kernel.org,
	peterz@...radead.org, mingo@...hat.com, vincent.guittot@...aro.org,
	wanpeng.li@...mail.com
Subject: Re: [PATCH 1/2] sched/deadline: add per rq tracking of admitted
 bandwidth

Hi Juri,

On Thu, 11 Feb 2016 12:12:57 +0000
Juri Lelli <juri.lelli@....com> wrote:
[...]
> I think we still have (at least) two problems:
> 
>  - select_task_rq_dl, if we select a different target
>  - select_task_rq might make use of select_fallback_rq, if
> cpus_allowed changed after the task went to sleep
> 
> Second case is what creates the problem here, as we don't update
> task_rq(p) and fallback_cpu ac_bw. I was thinking we might do so,
> maybe adding fallback_cpu in task_struct, from migrate_task_rq_dl()
> (it has to be added yes), but I fear that we should hold both rq
> locks :/.
> 
> Luca, did you already face this problem (if I got it right) and
> thought of a way to fix it? I'll go back and stare a bit more at
> those paths.
In my patch I took care of the first case (modifying
select_task_rq_dl() to move the utilization from the "old rq" to the
"new rq"), but I never managed to trigger select_fallback_rq() in my
tests, so I overlooked that case.


				Luca