linux-kernel - Re: [RFC PATCH 7/9] housekeeping: Use own boot option, independant from nohz

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Date:   Wed, 16 Aug 2017 20:00:44 +0200
From:   Mike Galbraith <efault@....de>
To:     Christopher Lameter <cl@...ux.com>
Cc:     "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
        Frederic Weisbecker <fweisbec@...il.com>,
        Luiz Capitulino <lcapitulino@...hat.com>,
        LKML <linux-kernel@...r.kernel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Chris Metcalf <cmetcalf@...lanox.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...nel.org>, Rik van Riel <riel@...hat.com>,
        Wanpeng Li <kernellwp@...il.com>
Subject: Re: [RFC PATCH 7/9] housekeeping: Use own boot option, independant
 from nohz

On Tue, 2017-08-15 at 11:26 -0500, Christopher Lameter wrote:
> On Tue, 15 Aug 2017, Mike Galbraith wrote:
> 
> > On Tue, 2017-08-15 at 10:52 -0500, Christopher Lameter wrote:
> > > On Tue, 15 Aug 2017, Paul E. McKenney wrote:
> > >
> > > > Don't the HPC guys just disable idle_balance(), or am I out of date again?
> > >
> > > Ummm.. Why does idle management matter when your goal is to keep all
> > > processor busy working at maximum throughput?
> >
> > If you _never_ idle, you never have to worry about it.  Is 100% CPU
> > until the end of time all there is to HPC?
> 
> Most of the time that is true for HPC loads. They may also go through a
> I/O throughput constrained processing phase or synchronization phase where
> idle activity occurs.

That synchronization is what I tend to get all hung up on pondering HPC
vs RT terminology.  Care and feeding of parallel pipelines has got to
be loaded to the gills with synchronization (intermediate math results
etc), rendering the sum event driven.

Doesn't matter, both acronyms reduce to latency intolerant.

	-Mike