linux-kernel - Re: [PATCH v3] sched/deadline: do not try to push tasks if pinned task switches to dl

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Date:	Wed, 30 Mar 2016 15:59:19 +0800
From:	Wanpeng Li <kernellwp@...il.com>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	Steven Rostedt <rostedt@...dmis.org>,
	Juri Lelli <juri.lelli@....com>,
	Wanpeng Li <wanpeng.li@...ux.intel.com>,
	Ingo Molnar <mingo@...hat.com>,
	Kirill V Tkhai <tkhai@...dex.ru>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v3] sched/deadline: do not try to push tasks if pinned
 task switches to dl

2016-03-30 14:44 GMT+08:00 Peter Zijlstra <peterz@...radead.org>:
> On Tue, Mar 29, 2016 at 06:47:22PM -0400, Steven Rostedt wrote:
>> I'm looking at some old changes for sched-deadline, and I stumbled
>> across this. As I'm working on sched deadline tests, I've discovered
>> that they can't have cpu affinity. They are limited to their sched
>> domains. That is, sched deadline tasks have whatever affinity that the

root domain I think.

>> domain they happen to be in has.
>>
>> Is there a condition where rq != task_rq(p) and p->nr_cpus_allowed > 1
>> isn't true?
>
> When holding rq->lock, no. I suppose the patch was just to mirror rt and
> someone 'forgot' about the extra constraints on dl tasks.
>

sched_class::switched_from() methods can drop rq->lock before your
great balance_callback patchset. :-)

Regards,
Wanpeng Li