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

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Message-ID: <4F2E7311.8060808@redhat.com>
Date:	Sun, 05 Feb 2012 14:16:17 +0200
From:	Avi Kivity <avi@...hat.com>
To:	paulmck@...ux.vnet.ibm.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 02/02/2012 07:51 PM, Paul E. McKenney wrote:
> 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?
>

Looks like there are new rcu_user_enter() and rcu_user_exit() APIs which
we can use.  Hopefully they subsume rcu_virt_note_context_switch() so we
only need one set of APIs.

-- 
error compiling committee.c: too many arguments to function

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