linux-kernel - Re: [PATCH 2/2] nohz: make nohz

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Date:	Sat, 04 Apr 2015 04:03:59 +0200
From:	Mike Galbraith <umgwanakikbuti@...il.com>
To:	Chris Metcalf <cmetcalf@...hip.com>
Cc:	"Peter Zijlstra (Intel)" <peterz@...radead.org>,
	Frederic Weisbecker <fweisbec@...il.com>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	"Rafael J. Wysocki" <rafael.j.wysocki@...el.com>,
	Martin Schwidefsky <schwidefsky@...ibm.com>,
	Ingo Molnar <mingo@...hat.com>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/2] nohz: make nohz_full imply isolcpus

On Fri, 2015-04-03 at 15:21 -0400, Chris Metcalf wrote:
> On 04/03/2015 02:08 PM, Mike Galbraith wrote:
> > On Fri, 2015-04-03 at 12:24 -0400,  cmetcalf@...hip.comwrote:
> > > From: Chris Metcalf <cmetcalf@...hip.com>
> > > 
> > > It's not clear that nohz_full is useful without isolcpus also
> > > set, since otherwise the scheduler has to run periodically to
> > > try to determine whether to steal work from other cores.
> > > 
> > > Signed-off-by: Chris Metcalf <cmetcalf@...hip.com>
> > Ack!  nohz_full= as currently defined makes zero sense when the cpu
> > set (which should be spelled cpuset) remains connected to the
> > scheduler.  Perturbation of tasks to PREVENT cpu domination is what
> > the scheduler does for a living.  Sprinkling microsecond savers all
> > over the kernel is pretty silly if you don't shut down the mother 
> > lode
> > of perturbation.
> 
> Sounds like a thumbs up for this patch, then?  :-)

Yup.  The other thumb turns in the up direction when folks start 
spelling cpuset properly ;-)  Static isolcpus was supposed to go away.

        -Mike
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