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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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