linux-kernel - Re: [stable] scheduler nice 19 versus 'idle' behavior / static low-priority scheduling

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Date:	Mon, 9 Feb 2009 07:51:44 -0800
From:	Greg KH <greg@...ah.com>
To:	Brian Rogers <brian@...w.org>
Cc:	Mike Galbraith <efault@....de>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Jan Engelhardt <jengelh@...ozas.de>,
	Ingo Molnar <mingo@...e.hu>,
	Nathanael Hoyle <nhoyle@...letech.com>,
	stable <stable@...nel.org>
Subject: Re: [stable] scheduler nice 19 versus 'idle' behavior / static
	low-priority scheduling

On Mon, Feb 09, 2009 at 07:19:36AM -0800, Brian Rogers wrote:
> Greg KH wrote:
>> On Sat, Jan 31, 2009 at 10:08:13AM +0100, Mike Galbraith wrote:
>>   
>>> On Sat, 2009-01-31 at 06:38 +0100, Mike Galbraith wrote:
>>>     
>>>> On Fri, 2009-01-30 at 14:12 -0800, Brian Rogers wrote:
>>>>       
>>>>> Mike Galbraith wrote:
>>>>>         
>>>>>> On Fri, 2009-01-30 at 02:59 -0500, Nathanael Hoyle wrote:
>>>>>>             
>>>>>>> I am running foldingathome under it at the moment, and it seems to be
>>>>>>> improving the situation somewhat, but I still need/want to test with
>>>>>>> Mike's referenced patches.
>>>>>>>                 
>>>>>> You will most definitely encounter evilness running SCHED_IDLE tasks 
>>>>>> in
>>>>>> a kernel without the SCHED_IDLE fixes.
>>>>>>             
>>>>> Speaking of SCHED_IDLE fixes, is 
>>>>> 6bc912b71b6f33b041cfde93ca3f019cbaa852bc going to be put into the next 
>>>>> stable 2.6.28 release? Without it on 2.6.28.2, I can still produce 
>>>>> minutes-long freezes with BOINC or other idle processes.
>>>>>
>>>>> With the above commit on top of 2.6.28.2 and also 
>>>>> cce7ade803699463ecc62a065ca522004f7ccb3d, the problem is solved, though 
>>>>> I assume cce7ad isn't actually required to fix that, and I can test 
>>>>> that if desired.
>>>>>         
>>>> I think they both should go to stable, but dunno if they're headed that
>>>> direction or not.
>>>>
>>>> One way to find out, CCs added.
>>>>       
>>> For those who may want to run SCHED_IDLE tasks in .27, I've integrated
>>> and lightly tested the fixes required to do so.  One additional commit
>>> was needed to get SCHED_IDLE vs nice 19 working right, namely f9c0b09.
>>> Without that, SCHED_IDLE tasks received more CPU than nice 19 tasks.
>>>
>>> Since .27 is in long-term maintenance, I'd integrate into stable, but
>>> that's not my decision.  Anyone who applies the below to their stable
>>> kernel gets to keep all the pieces should something break ;-)
>>>     
>>
>> I'm going to hold off and not do this, as it seems too risky.
>>
>> But thanks for the pointers, perhaps someone else will want to do this
>> for their distro kernels if they have problems with this.
>>   
>
> Is this statement meant to apply to both 2.6.27 and 2.6.28, or just 2.6.27?

Both.
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