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Date: Sun, 16 Oct 2016 21:40:59 +0200
From: Luca Abeni <luca.abeni@unitn.it>
To: Peter Zijlstra <peterz@infradead.org>
Cc: linux-kernel@vger.kernel.org,
        Tommaso Cucinotta <tommaso.cucinotta@sssup.it>,
        Juri Lelli <juri.lelli@gmail.com>,
        Thomas Gleixner <tglx@linutronix.de>,
        Andrea Parri <parri.andrea@gmail.com>,
        giuseppe lipari <giuseppe.lipari@lsv.ens-cachan.fr>,
        Claudio Scordino <claudio@evidence.eu.com>
Subject: Re: About group scheduling for SCHED_DEADLINE
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On Mon, 10 Oct 2016 13:08:18 +0200
Peter Zijlstra <peterz@infradead.org> wrote:

> On Mon, Oct 10, 2016 at 12:15:58PM +0200, Peter Zijlstra wrote:
> > However, I think there's a third alternative. I have memories of a
> > paper from UNC (I'd have to dig through the site to see if I can
> > still find it) where they argue that for a hierarchical (G-)FIFO
> > you should use minimal concurrency, that is run the minimal number
> > of (v)cpu servers.
> > 
> > This would mean we give a single CBS parameter and carve out the
> > minimal number (of max CBS) (v)cpu that fit in that.
> > 
> > I'm just not sure how the random affinity crap works out for that,
> > if we have the (v)cpu servers migratable in the G-EDF and migrate
> > to whatever is demanded by the task at runtime it might work, but
> > who knows.. Analysis would be needed I think.
> 
> Hurm,.. thinking slightly more on this, this ends up being a DL task
> with random affinity, which is problematic IIRC.
Yes, there currently is no existing schedulability analysis for
multi-processor EDF with random affinities (as far as I know), but I
think we can at least have a look at developing this kind of analysis.
Giuseppe, what do you think?



			Luca