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

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Date:	Thu, 11 Feb 2016 12:27:54 +0000
From:	Juri Lelli <juri.lelli@....com>
To:	luca abeni <luca.abeni@...tn.it>
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

On 11/02/16 13:22, Luca Abeni wrote:
> 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.
> 

Right, I was thinking to do the same. And you did that after grabbing
both locks, right?