Message-ID: <4F3A5F0B.2090309@redhat.com>
Date: Tue, 14 Feb 2012 15:18:03 +0200
From: Avi Kivity <avi@redhat.com>
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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>
Subject: Re: [v7 0/8] Reduce cross CPU IPI interference
References: <4F2AB66C.2030309@redhat.com> <20120202170134.GM2518@linux.vnet.ibm.com> <4F2AC69B.7000704@redhat.com> <20120202175155.GV2518@linux.vnet.ibm.com> <4F2E7311.8060808@redhat.com> <20120205165927.GH2467@linux.vnet.ibm.com> <20120209152155.GA22552@somewhere.redhat.com> <4F33EEB3.4080807@redhat.com> <20120209182216.GG22552@somewhere.redhat.com> <20120209234144.GC2458@linux.vnet.ibm.com> <20120210013911.GM22552@somewhere.redhat.com>
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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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