Date: Wed, 1 Feb 2012 12:13:36 -0800
From: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>
To: Christoph Lameter <cl@linux.com>
Cc: 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>, Avi Kivity <avi@redhat.com>,
        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 Wed, Feb 01, 2012 at 02:06:07PM -0600, Christoph Lameter wrote:
> On Wed, 1 Feb 2012, Paul E. McKenney wrote:
> 
> > On Wed, Feb 01, 2012 at 06:35:22PM +0100, Peter Zijlstra wrote:
> > > On Sun, 2012-01-29 at 10:25 +0200, Gilad Ben-Yossef wrote:
> > > >
> > > > If this is of interest, I keep a list tracking global IPI and global
> > > > task schedulers sources in the core kernel here:
> > > > https://github.com/gby/linux/wiki.
> > >
> > > You can add synchronize_.*_expedited() to the list, it does its best to
> > > bash the entire machine in order to try and make RCU grace periods
> > > happen fast.
> >
> > I have duly added "Make synchronize_sched_expedited() avoid IPIing idle
> > CPUs" to http://kernel.org/pub/linux/kernel/people/paulmck/rcutodo.html.
> >
> > This should not be hard once I have built up some trust in the new
> > RCU idle-detection code.  It would also automatically apply to
> > Frederic's dyntick-idle userspace work.
> 
> Could we also apply the same approach to processors busy doing
> computational work? In that case the OS is also not needed. Interrupting
> these activities is impacting on performance and latency.

Yep, that is in fact what Frederic's dyntick-idle userspace work does.

							Thanx, Paul

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