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

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Date:	Thu, 3 Mar 2011 20:59:29 +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

On Thu, Mar 3, 2011 at 7:35 PM, Yong Zhang <yong.zhang0@...il.com> wrote:
> On Thu, Mar 03, 2011 at 05:04:35PM +0530, Balbir Singh wrote:
>> Fix hierarchical scheduling in sched rt group
>>
>> From: Balbir Singh <balbir@...ux.vnet.ibm.com>
>>
>> The current sched rt code is broken when it comes to hierarchical
>> scheduling, this patch fixes two problems
>>
>> 1. It adds redundant enqueuing (harmless) when it finds a queue
>>    has tasks enqueued, but it has no run time and it is not
>>    throttled.
>
> You say redundant here, so in fact we don't need it, right?
>

No, not really :) It is required, it is a backup check to see if we
have queued tasks, rt_time of 0 and the runqueue is not throttled, why
should it be dequeued?

>> 2. The most important change is in sched_rt_rq_enqueue/dequeue.
>>    The code just picks the rt_rq belonging to the current cpu
>>    on which the period timer runs, the patch fixes it, so that
>>    the correct rt_se is enqueued/dequeued.
>
> Ah, this is true. It is also needed for stable-2.6.33+
>

Yep, we'll need backports to stable versions

Balbir
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