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: <1227552397.4259.504.camel@twins>
Date:	Mon, 24 Nov 2008 19:46:37 +0100
From:	Peter Zijlstra <a.p.zijlstra@...llo.nl>
To:	vatsa@...ibm.com
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, 2008-11-24 at 22:35 +0530, Srivatsa Vaddagiri wrote:
> 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.

I'm fine with just not showing RT tasks in cgroup:cpu/tasks.

> 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.

Right, that might take a bit of time still as RT_GROUP needs a deadline
scheduler to be complete.

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