Date: Thu, 2 Feb 2012 09:51:55 -0800
From: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>
To: Avi Kivity <avi@redhat.com>
Cc: Christoph Lameter <cl@linux.com>, Peter Zijlstra <a.p.zijlstra@chello.nl>,
        Gilad Ben-Yossef <gilad@benyossef.com>, linux-kernel@vger.kernel.org,
        Chris Metcalf <cmetcalf@tilera.com>,
        Frederic Weisbecker <fweisbec@gmail.com>, linux-mm@kvack.org,
        Pekka Enberg <penberg@kernel.org>, Matt Mackall <mpm@selenic.com>,
        Sasha Levin <levinsasha928@gmail.com>, Rik van Riel <riel@redhat.com>,
        Andi Kleen <andi@firstfloor.org>, Mel Gorman <mel@csn.ul.ie>,
        Andrew Morton <akpm@linux-foundation.org>,
        Alexander Viro <viro@zeniv.linux.org.uk>,
        Michal Nazarewicz <mina86@mina86.com>,
        Kosaki Motohiro <kosaki.motohiro@gmail.com>,
        Milton Miller <miltonm@bga.com>
Subject: Re: [v7 0/8] Reduce cross CPU IPI interference
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On Thu, Feb 02, 2012 at 07:23:39PM +0200, Avi Kivity wrote:
> On 02/02/2012 07:01 PM, Paul E. McKenney wrote:
> > > 
> > > It's not called (since the cpu is not idle).  Instead we call
> > > rcu_virt_note_context_switch().
> >
> > Frederic's work checks to see if there is only one runnable user task
> > on a given CPU.  If there is only one, then the scheduling-clock interrupt
> > is turned off for that CPU, and RCU is told to ignore it while it is
> > executing in user space.  Not sure whether this covers KVM guests.
> 
> Conceptually it's the same.  Maybe it needs adjustments, since kvm
> enters a guest in a different way than the kernel exits to userspace.
> 
> > In any case, this is not yet in mainline.
> 
> Let me know when it's in, and I'll have a look.

Could you please touch base with Frederic Weisbecker to make sure that
what he is doing works for you?

							Thanx, Paul

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