linux-kernel - Re: [BUGFIX][PATCH] Fix sched rt group scheduling when hierachy is enabled

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Date:	Fri, 4 Mar 2011 14:29:08 +0530
From:	Balbir Singh <balbir@...ux.vnet.ibm.com>
To:	Yong Zhang <yong.zhang0@...il.com>
Cc:	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Ingo Molnar <mingo@...e.hu>,
	Peter Zijlstra <pzijlstr@...hat.com>,
	Srivatsa Vaddagiri <vatsa@...ux.vnet.ibm.com>,
	Bharata B Rao <bharata.rao@...ibm.com>
Subject: Re: [BUGFIX][PATCH] Fix sched rt group scheduling when hierachy is enabled

>>>  deactivate_task(b); /* A.throttled == 1 && A.rt_nr_running == 0 */
>>>    do_sched_rt_period_timer(); /* A.run_time == 0 && A.throttled == 0*/
>>
>> Note at some point rt_time becomes 0 and if enqueue is not set, the
>
> If the group should be add back, it will be at the first
> do_sched_rt_period_timer() which decreases run_time;
>

As long as idle is 0, the period will continue to run, if it has
rt_nr_running or rt_time, the timer will run.

>> next do_sched_rt_period_timer() is a NOP and does not enqueue back the
>> group
>
> Otherwise it will be added back when a task is attching to it.
>
> I still can't see how a unthrottled group which has task attched stay
> unqueued.

The other way of looking at the first change is

Can we have rt_time as 0, rt_nr_running >=1, rt_throttled !=0 and
still not have the rt_rq enqueued?

If this is not the case, we don't lose much, a quick check for
rt_nr_running and on_rt_q

Balbir
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