linux-kernel - Re: [PATCH 07/41] cpuset: Set up interface for nohz flag

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Message-ID: <1336574836.16079.17.camel@marge.simpson.net>
Date:	Wed, 09 May 2012 16:47:16 +0200
From:	Mike Galbraith <efault@....de>
To:	Christoph Lameter <cl@...ux.com>
Cc:	Peter Zijlstra <peterz@...radead.org>,
	Frederic Weisbecker <fweisbec@...il.com>,
	LKML <linux-kernel@...r.kernel.org>,
	linaro-sched-sig@...ts.linaro.org,
	Alessio Igor Bogani <abogani@...nel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Avi Kivity <avi@...hat.com>,
	Chris Metcalf <cmetcalf@...era.com>,
	Daniel Lezcano <daniel.lezcano@...aro.org>,
	Geoff Levand <geoff@...radead.org>,
	Gilad Ben Yossef <gilad@...yossef.com>,
	Hakan Akkan <hakanakkan@...il.com>,
	Ingo Molnar <mingo@...nel.org>, Kevin Hilman <khilman@...com>,
	Max Krasnyansky <maxk@...lcomm.com>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	Stephen Hemminger <shemminger@...tta.com>,
	Steven Rostedt <rostedt@...dmis.org>,
	Sven-Thorsten Dietrich <thebigcorporation@...il.com>,
	Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [PATCH 07/41] cpuset: Set up interface for nohz flag

On Wed, 2012-05-09 at 09:22 -0500, Christoph Lameter wrote: 
> On Wed, 9 May 2012, Mike Galbraith wrote:

> > > isolcpus are not part of load balancer domains.
> >
> > Yup, so if you have an application with an RT component, somewhat
> > sensitive, needs isolation from rest of a big box, but app also has
> > SCHED_OTHER components.  isolcpus is a pain, everything has to be static
> > and nailed to the floor.  Load just works when plugged into a cpuset.
> 
> Well you have low latency requirements. If you code for lowest latency
> then you have to consider cache sizes, cache sharing etc etc. This means
> you will have to nail down everything anyways. Cpusets would just be
> another thing that one has to worry about.
> 
> The loads definitely wont work right if just "plugged into a cpuset".

You're talking about serious RT/HPC.  I'm talking about apps/loads with
modest requirements, like "Please keep that evil nVidia (this that the
other) thing the _hell_ away from me, I cannot deal with it's futzing
around in the kernel for a _full second_ at a time".

-Mike

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