linux-kernel - Re: [v7 0/8] Reduce cross CPU IPI interference

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Message-ID: <20120201201336.GI2382@linux.vnet.ibm.com>
Date:	Wed, 1 Feb 2012 12:13:36 -0800
From:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
To:	Christoph Lameter <cl@...ux.com>
Cc:	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Gilad Ben-Yossef <gilad@...yossef.com>,
	linux-kernel@...r.kernel.org, Chris Metcalf <cmetcalf@...era.com>,
	Frederic Weisbecker <fweisbec@...il.com>, linux-mm@...ck.org,
	Pekka Enberg <penberg@...nel.org>,
	Matt Mackall <mpm@...enic.com>,
	Sasha Levin <levinsasha928@...il.com>,
	Rik van Riel <riel@...hat.com>,
	Andi Kleen <andi@...stfloor.org>, Mel Gorman <mel@....ul.ie>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Alexander Viro <viro@...iv.linux.org.uk>,
	Avi Kivity <avi@...hat.com>,
	Michal Nazarewicz <mina86@...a86.com>,
	Kosaki Motohiro <kosaki.motohiro@...il.com>,
	Milton Miller <miltonm@....com>
Subject: Re: [v7 0/8] Reduce cross CPU IPI interference

On Wed, Feb 01, 2012 at 02:06:07PM -0600, Christoph Lameter wrote:
> On Wed, 1 Feb 2012, Paul E. McKenney wrote:
> 
> > On Wed, Feb 01, 2012 at 06:35:22PM +0100, Peter Zijlstra wrote:
> > > On Sun, 2012-01-29 at 10:25 +0200, Gilad Ben-Yossef wrote:
> > > >
> > > > If this is of interest, I keep a list tracking global IPI and global
> > > > task schedulers sources in the core kernel here:
> > > > https://github.com/gby/linux/wiki.
> > >
> > > You can add synchronize_.*_expedited() to the list, it does its best to
> > > bash the entire machine in order to try and make RCU grace periods
> > > happen fast.
> >
> > I have duly added "Make synchronize_sched_expedited() avoid IPIing idle
> > CPUs" to http://kernel.org/pub/linux/kernel/people/paulmck/rcutodo.html.
> >
> > This should not be hard once I have built up some trust in the new
> > RCU idle-detection code.  It would also automatically apply to
> > Frederic's dyntick-idle userspace work.
> 
> Could we also apply the same approach to processors busy doing
> computational work? In that case the OS is also not needed. Interrupting
> these activities is impacting on performance and latency.

Yep, that is in fact what Frederic's dyntick-idle userspace work does.

							Thanx, Paul

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