linux-kernel - Re: [patch] Re: autogroup: sched

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Message-ID: <20110218110955.GA3124@siel.b>
Date:	Fri, 18 Feb 2011 12:09:55 +0100
From:	torbenh <torbenh@....de>
To:	Mike Galbraith <efault@....de>
Cc:	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Yong Zhang <yong.zhang0@...il.com>, bharata@...ux.vnet.ibm.com,
	Ingo Molnar <mingo@...e.hu>, linux-kernel@...r.kernel.org,
	tglx@...utronix.de
Subject: Re: [patch] Re: autogroup: sched_setscheduler() fails

On Tue, Feb 15, 2011 at 05:43:30PM +0100, Mike Galbraith wrote:
> On Tue, 2011-02-15 at 16:46 +0100, torbenh wrote:
> > On Mon, Jan 17, 2011 at 02:16:00PM +0100, Peter Zijlstra wrote:
> > > On Thu, 2011-01-13 at 04:54 +0100, Mike Galbraith wrote:
> > > > sched, autogroup: fix CONFIG_RT_GROUP_SCHED sched_setscheduler() failure.
> > > > 
> > > > If CONFIG_RT_GROUP_SCHED is set, __sched_setscheduler() fails due to autogroup
> > > > not allocating rt_runtime.  Free unused/unusable rt_se and rt_rq, redirect RT
> > > > tasks to the root task group, and tell __sched_setscheduler() that it's ok.
> > > > 
> > > > Signed-off-by: Mike Galbraith <efault@....de>
> > > > Reported-by: Bharata B Rao <bharata@...ux.vnet.ibm.com>
> > > 
> > > Thanks, applied!
> > 
> > while this behaviour is certeinly necessary, i think this is a hack.
> > it fixes the problem for autogroups.
> > But its not fixed for things which want to control the cfs shares via
> > normal cgroups.
> 
> You mean automated control ala systemd?  For a static set of groups, it
> works fine.  I was wondering how systemd would deal with it.

but i can not get the same behaviour as if CONFIG_RT_GROUP_SCHED was
off. iE N cgroups with different cpu.share values, but each with
rt_runtime_us=950000

if the rt_runtime_us was in a different subsystem, its my understanding
that i could leave rt_runtime_us alone, and have all tasks in the root
group in the rt_runtime subsystem.

> 
> > why isnt rt_runtime_us residing in a separate (new) subsystem ?
> 
> The allocation problem was shamelessly punted back to the user, where I
> think it truly belongs.

sure it belongs to the user. but what if user wants to have different
cpu.shares, but full rt_runtime_us for all tasks ?

i can not have 2 sibling cgroups, whose rt_runtime_us adds up to over
the rt_period ...



> 
> 	-Mike
> 
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-- 
torben Hohn
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