Date: Fri, 18 Feb 2011 14:40:50 +0100
From: torbenh <torbenh@gmx.de>
To: Mike Galbraith <efault@gmx.de>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>,
        Yong Zhang <yong.zhang0@gmail.com>, bharata@linux.vnet.ibm.com,
        Ingo Molnar <mingo@elte.hu>, linux-kernel@vger.kernel.org,
        tglx@linutronix.de
Subject: Re: [patch] Re: autogroup: sched_setscheduler() fails
Message-ID: <20110218134050.GF3124@siel.b>
Mail-Followup-To: Mike Galbraith <efault@gmx.de>,
	Peter Zijlstra <a.p.zijlstra@chello.nl>,
	Yong Zhang <yong.zhang0@gmail.com>, bharata@linux.vnet.ibm.com,
	Ingo Molnar <mingo@elte.hu>, linux-kernel@vger.kernel.org,
	tglx@linutronix.de
References: <20110111171046.GL4772@in.ibm.com>
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 <1294890890.8089.39.camel@marge.simson.net>
 <1295270160.30950.96.camel@laptop>
 <20110215154612.GI3055@siel.b>
 <1297788210.15382.51.camel@marge.simson.net>
 <20110218110955.GA3124@siel.b>
 <1298033412.8735.30.camel@marge.simson.net>
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On Fri, Feb 18, 2011 at 01:50:12PM +0100, Mike Galbraith wrote:
> On Fri, 2011-02-18 at 12:09 +0100, torbenh wrote:
> > 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@gmx.de>
> > > > > > Reported-by: Bharata B Rao <bharata@linux.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 CONFIG_RT_GROUP_SCHED was a noop, it wouldn't exist.
> 
> > 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.
>  
> Sounds like you just want to turn CONFIG_RT_GROUP_SCHED off.
> 
> > > 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 ?
> 
> Then the user doesn't want CONFIG_RT_GROUP_SCHED set.

many users dont configure their kernels themselves.
and this setting is not dynamic.

i guess its highly unlikely any normal user wants CONFIG_RT_GROUP_SCHED.
but maybe distros will turn it on. 

-- 
torben Hohn
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