linux-kernel - Re: [PATCH 2/2] RT: remove "paranoid" limit in push_rt

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Date:	Fri, 03 Oct 2008 13:27:34 -0400
From:	Gregory Haskins <ghaskins@...ell.com>
To:	Gilles Carry <Gilles.Carry@...l.net>,
	Gregory Haskins <ghaskins@...ell.com>,
	linux-rt-users@...r.kernel.org, linux-kernel@...r.kernel.org,
	rostedt@...dmis.org, dvhltc@...ibm.com, dino@...ibm.com
Subject: Re: [PATCH 2/2] RT: remove "paranoid" limit in push_rt_task

Chirag Jog wrote:
> * Gilles Carry <Gilles.Carry@...l.net> [2008-10-03 15:46:59]:
>
>   
>> Sorry Greg,
>>
>> Neither PPC64 nor Intel64 make it with this patch.
>> At boot time, it stops at the BUG_ON you added:
>> 0xc00000000004eca4 is in push_rt_task (kernel/sched_rt.c:1102)
>>     
> I am also confirming this issue gilles reported.
>
> Although, i have a question:
> When we enable group scheduling (CONFIG_RT_GROUP_SCHED),
> all the problems disappear.
> After skimming through the rt scheduler code, I don't feel group 
> scheduling alters the behavior of push/pull strategies in any way.
>
> So I am wonder whether enabling group scheduling
> actually solves the problem or just makes it tough 
> to recreate?
>   
Hi Chirag,


The issue that Gilles pointed me at is a race condition.  I do not
suspect GROUP_SCHED itself has anything to do with the problem other
than it changes the timing.  HTH!

-Greg




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