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

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Message-ID: <20120202153437.GD2518@linux.vnet.ibm.com>
Date:	Thu, 2 Feb 2012 07:34:37 -0800
From:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
To:	Avi Kivity <avi@...hat.com>
Cc:	Christoph Lameter <cl@...ux.com>,
	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>,
	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 Thu, Feb 02, 2012 at 11:34:25AM +0200, Avi Kivity wrote:
> On 02/01/2012 10:13 PM, Paul E. McKenney wrote:
> > > 
> > > 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.
> 
> Running in a guest is a special case of running in userspace, so we'd
> need to extend this work to kvm as well.

As long as rcu_idle_enter() is called at the appropriate time, RCU will
happily ignore the CPU.  ;-)

							Thanx, Paul

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