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Date: Tue, 14 Feb 2012 15:18:03 +0200
From: Avi Kivity <avi@redhat.com>
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Subject: Re: [v7 0/8] Reduce cross CPU IPI interference
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To: Frederic Weisbecker <fweisbec@gmail.com>
Cc: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>, 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>, 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>

On 02/10/2012 03:39 AM, Frederic Weisbecker wrote:
> > 
> > As long as the code doesn't enter RCU read-side critical sections in
> > the time between rcu_idle_enter() and rcu_idle_exit(), this should
> > work fine.
>
> This should work fine yeah but further the correctness, I wonder if this
> is going to be a win.
>
> We use rcu_idle_enter() in idle to avoid to keep the tick for RCU. But
> what about falling into guest mode? I guess the tick is kept there
> so is it going to be a win in throughput or something to use rcu_idle_enter()?

We could disable the tick while in guest mode as well.  Interrupts in
guest mode are even more expensive than interrupts in user mode.

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

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