Message-ID: <48E65606.6040409@novell.com>
Date: Fri, 03 Oct 2008 13:27:34 -0400
From: Gregory Haskins <ghaskins@novell.com>
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To: Gilles Carry <Gilles.Carry@bull.net>,
       Gregory Haskins <ghaskins@novell.com>, linux-rt-users@vger.kernel.org,
       linux-kernel@vger.kernel.org, rostedt@goodmis.org, dvhltc@us.ibm.com,
       dino@in.ibm.com
Subject: Re: [PATCH 2/2] RT: remove "paranoid" limit in push_rt_task
References: <20081003123745.17387.61782.stgit@dev.haskins.net> <20081003124305.17387.90233.stgit@dev.haskins.net> <48E62253.1090000@bull.net> <20081003154501.GB5032@linux.vnet.ibm.com>
In-Reply-To: <20081003154501.GB5032@linux.vnet.ibm.com>
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Chirag Jog wrote:
> * Gilles Carry <Gilles.Carry@bull.net> [2008-10-03 15:46:59]:
>
>  =20
>> 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)
>>    =20
> 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=20
> 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=20
> to recreate?
>  =20
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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