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

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Message-ID: <4F3A5F0B.2090309@redhat.com>
Date:	Tue, 14 Feb 2012 15:18:03 +0200
From:	Avi Kivity <avi@...hat.com>
To:	Frederic Weisbecker <fweisbec@...il.com>
CC:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	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>,
	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 02/10/2012 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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