linux-kernel - Re: Another SCHED_DEADLINE bug (with bisection and possible fix)

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Date:	Wed, 07 Jan 2015 14:14:11 +0100
From:	Luca Abeni <luca.abeni@...tn.it>
To:	tkhai@...dex.ru
CC:	Peter Zijlstra <peterz@...radead.org>,
	Ingo Molnar <mingo@...hat.com>,
	Juri Lelli <juri.lelli@...il.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: Another SCHED_DEADLINE bug (with bisection and possible fix)

On 01/07/2015 02:04 PM, Kirill Tkhai wrote:
[...]
>>> and further enqueue_task() places it on the dl_rq.
>> I was under the impression that no further enqueue_task() will happen (since
>> the task is throttled, it is not on runqueue, so __sched_setscheduler() will
>> not dequeue/enqueue it).
>> But I am probably missing something else :)
>
> We have two concept of "on runqueue". The first one is rq->on_rq. It means
> that a task is "queued". The second is on_dl_rq(dl_se).
>
> When task is not "queued", it's always not on dl_rq.
>
> When task is "queued" it may be in two states:
> 1)on_dl_rq() -- this means the task is not throttled;
> 2)!on_dl_rq() -- is task as throttled.
>
> So when we are discussing about a throttled task, the task is "queued". If
> you clear dl_throttled, __sched_setscheduler() places it back it the both
> meaning: on_rq and on_dl_rq, and the task becomes available for picking
> in __schedule().
Ah, I see. Thanks for explaining! Now, everything is more clear and I agree
with you.

[...]
> Does my patch help you? It helps me, but anyway I need your confirmation.
I am just back from vacations, and I had no time to test it yet... I hope to
test it before the end of the week, and I'll let you know (but now I am convinced
that it should help).



			Thanks again,
				Luca

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