linux-kernel - Re: [RFC][PATCH 13/22] sched: add resource limits for -deadline tasks

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Date:	Sat, 13 Nov 2010 00:32:21 +0100
From:	Peter Zijlstra <peterz@...radead.org>
To:	Raistlin <raistlin@...ux.it>
Cc:	Ingo Molnar <mingo@...e.hu>, Thomas Gleixner <tglx@...utronix.de>,
	Steven Rostedt <rostedt@...dmis.org>,
	Chris Friesen <cfriesen@...tel.com>, oleg@...hat.com,
	Frederic Weisbecker <fweisbec@...il.com>,
	Darren Hart <darren@...art.com>,
	Johan Eker <johan.eker@...csson.com>,
	"p.faure" <p.faure@...tech.ch>,
	linux-kernel <linux-kernel@...r.kernel.org>,
	Claudio Scordino <claudio@...dence.eu.com>,
	michael trimarchi <trimarchi@...is.sssup.it>,
	Fabio Checconi <fabio@...dalf.sssup.it>,
	Tommaso Cucinotta <cucinotta@...up.it>,
	Juri Lelli <juri.lelli@...il.com>,
	Nicola Manica <nicola.manica@...i.unitn.it>,
	Luca Abeni <luca.abeni@...tn.it>,
	Dhaval Giani <dhaval@...is.sssup.it>,
	Harald Gustafsson <hgu1972@...il.com>,
	paulmck <paulmck@...ux.vnet.ibm.com>
Subject: Re: [RFC][PATCH 13/22] sched: add resource limits for -deadline
 tasks

On Fri, 2010-11-12 at 22:30 +0100, Raistlin wrote:
> On Thu, 2010-11-11 at 20:57 +0100, Peter Zijlstra wrote:
> > > In fact, this patch:
> > >  - adds the resource limit RLIMIT_DLDLINE, which is the minimum value
> > >    a user task can use as its own deadline;
> > >  - adds the resource limit RLIMIT_DLRTIME, which is the maximum value
> > >    a user task can use as it own runtime.
> > > 
> >
> > We might also want to add an additional !SYS_CAP_ADMIN global bandwidth
> > cap much like the existing sysctl bandwidth cap.
> > 
> Mmm... I think we've never discussed much about that before, so here I
> am. I'm currently asking one to be root to set SCHED_DEADLINE as his
> policy. Normal users are allowed to do so, but just under the rlimits
> restrictions provided by this patch.
> 
> So, first of all, are we cool with this? Or do we want normal users to
> be able to give their tasks SCHED_DEADLINE policy by default? 

I think so, it would make it much more useful to people.

> Maybe we want that but up to a certain bandwidth?

Exactly.

>  Is this that you mean here,
> having two bandwidth limits, one of which !SYS_ADMINs could not cross?

Yep. A bandwidth cap for !SYS_CAP_ADMIN and a these two constraints
already introduced by this patch, a min period to avoid very fast timer
programming and a max runtime to avoid incurring large latencies on the
rest of the system.



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