linux-kernel - Re: About group scheduling for SCHED

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Message-ID: <20161016214059.65ac35b6@utopia>
Date:   Sun, 16 Oct 2016 21:40:59 +0200
From:   Luca Abeni <luca.abeni@...tn.it>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     linux-kernel@...r.kernel.org,
        Tommaso Cucinotta <tommaso.cucinotta@...up.it>,
        Juri Lelli <juri.lelli@...il.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Andrea Parri <parri.andrea@...il.com>,
        giuseppe lipari <giuseppe.lipari@....ens-cachan.fr>,
        Claudio Scordino <claudio@...dence.eu.com>
Subject: Re: About group scheduling for SCHED_DEADLINE

On Mon, 10 Oct 2016 13:08:18 +0200
Peter Zijlstra <peterz@...radead.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