linux-kernel - Re: [PATCH] sched: Don't allow priority switch to realtime when the task doesn't belong to init_task_group and when CONFIG_RT_GROUP

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Message-ID: <20081124170535.GE5451@linux.vnet.ibm.com>
Date:	Mon, 24 Nov 2008 22:35:35 +0530
From:	Srivatsa Vaddagiri <vatsa@...ibm.com>
To:	Peter Zijlstra <a.p.zijlstra@...llo.nl>
Cc:	bharata@...ux.vnet.ibm.com, linux-kernel@...r.kernel.org,
	Ingo Molnar <mingo@...e.hu>,
	Dhaval Giani <dhaval@...ux.vnet.ibm.com>
Subject: Re: [PATCH] sched: Don't allow priority switch to realtime when
	the task doesn't belong to init_task_group and when
	CONFIG_RT_GROUP_SCHED isn't set

On Mon, Nov 24, 2008 at 09:32:06AM +0100, Peter Zijlstra wrote:
> >  And may be as Ingo
> > suggested they should be moved to init_task_group.
> 
> Bzzt, wrong! They should not be moved to any group, they cannot be moved
> to any group, as they are group invariant.

Though what you say makes sense, the confusion arises from existing
cgroup<->scheduler interface, which can end up showing the above
single-set of RT-tasks to be split into multiple sets.

RT Tasks -> {RT0, RT1}

can be shown as:

	/a/tasks {RT0, ...}
	/b/tasks {RT1, ...}

Does this cause any problems? Perhaps no, just seems odd ..

Fixing this oddity of representing single RT-tasks set as multiple is not a 
cgroup issue IMHO.

P.S :- If eventually RT_GROUP_SCHED will be merged with FAIR_GROUP_SCHED, then 
it may make sense for us to just ignore this oddity for timebeing and look 
forward to the options being merged.

- vatsa
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