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

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Date:	Wed, 11 Sep 2013 16:53:26 +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 Wed, 2013-09-11 at 14:21 +0000, Christoph Lameter wrote: 
> On Wed, 11 Sep 2013, Mike Galbraith wrote:
> 
> > 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.
> 
> cpusets is being replaced by cgropus. And the mechanism adds some
> significant latencies to core memory management processing path.

You don't have to use or even configure in all controllers.

> Also many folks in finance like to deal directly with the hardware
> (processor numbers, affinity masks etc). There are already numerous ways
> to specify these masks. Pretty well established. Digging down a cpuset
> hierachy is a bit tedious. Then these cpusets can also overlap which
> makes the whole setup difficult.

These kind of things have to be exclusive set attributes 'course,
overlapping nohz_tick/full/off just ain't gonna work very well.

I hacked it up for my rt kernel to turn the tick on/off, and disable rt
load balancing (cpupri adds jitter) on a per exclusive set basis.  The
cpuset bit is easy.  Connecting buttons to scheduler and whatnot can
make cute little "You'd better not EVER submit this" warts though :)

> If cpusets can be used on top then ok but I would like it not to be
> required to have that compiled in.

IMHO, it makes much more sense to unify set attributes in cpusets,
fixing up or griping about whatever annoys HPC boxen/folks.

But whatever, I only piped in to mention that isolcpus wants to die, and
I've done that, so I can pipe-down now.

-Mike


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