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Subject: Re: [RFC][PATCH 13/22] sched: add resource limits for -deadline
 tasks
From: Peter Zijlstra <peterz@infradead.org>
To: Raistlin <raistlin@linux.it>
Cc: Ingo Molnar <mingo@elte.hu>, Thomas Gleixner <tglx@linutronix.de>,
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Date: Sat, 13 Nov 2010 00:32:21 +0100
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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.