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

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Message-ID: <0000014109b5ec0e-ca64a736-ce4a-4be2-abf6-bbf2c1c15f80-000000@email.amazonses.com>
Date:	Tue, 10 Sep 2013 21:10:20 +0000
From:	Christoph Lameter <cl@...ux.com>
To:	Gilad Ben-Yossef <gilad@...yossef.com>
cc:	Mike Galbraith <bitbucket@...ine.de>,
	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, 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.

isolcpus is broken as far as I can tell. Lets lay it to rest and come up
with a sane way to configure these things. Autoconfig if possible.



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