linux-kernel - Re: About group scheduling for SCHED

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Date:   Mon, 10 Oct 2016 13:08:18 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Luca Abeni <luca.abeni@...tn.it>
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>
Subject: Re: About group scheduling for SCHED_DEADLINE

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.