linux-kernel - Re: [PATCH] sched/rt: Fix rq's cpupri leak while enqueue/dequeue child RT entities

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Message-Id: <122071387281778@web18h.yandex.ru>
Date:	Tue, 17 Dec 2013 16:02:58 +0400
From:	Kirill Tkhai <tkhai@...dex.ru>
To:	Peter Zijlstra <peterz@...radead.org>,
	Ingo Molnar <mingo@...nel.org>
Cc:	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Steven Rostedt <rostedt@...dmis.org>,
	"stable@...r.kernel.org" <stable@...r.kernel.org>
Subject: Re: [PATCH] sched/rt: Fix rq's cpupri leak while enqueue/dequeue child RT entities



13.12.2013, 19:42, "Peter Zijlstra" <peterz@...radead.org>:
> On Wed, Nov 27, 2013 at 07:59:13PM +0400, Kirill Tkhai wrote:
>
>>  This patch touches RT group scheduling case.
>>
>>  Functions inc_rt_prio_smp() and dec_rt_prio_smp() change (global) rq's priority,
>>  while rt_rq passed to them may be not the top-level rt_rq. This is wrong, because
>>  changing of priority on a child level does not guarantee that the priority is
>>  the highest all over the rq. So, this leak makes RT balancing unusable.
>>
>>  The short example: the task having the highest priority among all rq's RT tasks
>>  (no one other task has the same priority) are waking on a throttle rt_rq.
>>  The rq's cpupri is set to the task's priority equivalent, but real
>>  rq->rt.highest_prio.curr is less.
>>
>>  The patch below fixes the problem.
>>
>>  It looks like all version have this bug, so I CC'ed stable mailing list.
>
> Yeah, I think this is right.
>
> cpupri stuff should indeed only be changed for the top level group.

Ingo, are you going to apply this patch? Or will you give any comments?
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