linux-kernel - Re: [RFC] Restrict kernel spawning of threads to a specified set of cpus.

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Message-ID: <1378869632.5476.34.camel@marge.simpson.net>
Date:	Wed, 11 Sep 2013 05:20:32 +0200
From:	Mike Galbraith <bitbucket@...ine.de>
To:	Christoph Lameter <cl@...ux.com>
Cc:	Gilad Ben-Yossef <gilad@...yossef.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Mike Frysinger <vapier@...too.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
Subject: Re: [RFC] Restrict kernel spawning of threads to a specified set of
 cpus.

On Tue, 2013-09-10 at 21:10 +0000, Christoph Lameter wrote: 
> On Tue, 10 Sep 2013, Gilad Ben-Yossef wrote:
> 
> > On Tue, Sep 10, 2013 at 10:26 AM, Mike Galbraith <bitbucket@...ine.de> wrote:
> >
> > >
> > > Hammering on the wrong spot makes removing isolcpus take longer, and
> > > adds up to more hammering in the long run, no?  Hearing you mention
> > > isolcpus, I just thought I should mention that it wants to go away, so
> > > might not be the optimal spot for isolation related tinkering.
> >
> >
> > OK, so I'll bite - isolcpu currently has special magic to do its thing but AFAIK
> > part of the reason isolcpu works "better" (for some definition of
> > better, for some
> > work loads) is simply because it blocks migration earlier than you get with
> > cpusets.
> >
> > What if we  re-did the implementation of isolcpu as creating an
> > cpuset with migration off as early as possible in the boot process, prior to
> > spawning init?
> >
> > So basically, isolcpus becomes just a way to configure a cpuset early?
> 
> I surely wish we had the ability to use tickless without the need for
> things like cpusets etc.

Mind saying why?  To me, creating properties of exclusive sets of CPUs
that the interface which manages sets and their properties is not fully
aware of is a dainbramaged thing to do.  

-Mike

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