From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932622Ab2FHE2m (ORCPT ); Fri, 8 Jun 2012 00:28:42 -0400 Received: from e4.ny.us.ibm.com ([32.97.182.144]:53479 "EHLO e4.ny.us.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751550Ab2FHE1r (ORCPT ); Fri, 8 Jun 2012 00:27:47 -0400 Date: Thu, 7 Jun 2012 15:45:08 -0700 From: "Paul E. McKenney" To: Frederic Weisbecker Cc: Ingo Molnar , LKML , Alessio Igor Bogani , Andrew Morton , Avi Kivity , Chris Metcalf , Christoph Lameter , Daniel Lezcano , Geoff Levand , Gilad Ben Yossef , Hakan Akkan , Kevin Hilman , Max Krasnyansky , Peter Zijlstra , Stephen Hemminger , Steven Rostedt , Sven-Thorsten Dietrich , Thomas Gleixner Subject: Re: [PATCH 0/2] rcu: Extended quiescent state for adaptive nohz Message-ID: <20120607224508.GX19601@linux.vnet.ibm.com> Reply-To: paulmck@linux.vnet.ibm.com References: <1338811708-18819-1-git-send-email-fweisbec@gmail.com> <20120604181313.GL2490@linux.vnet.ibm.com> <20120604210709.GO2490@linux.vnet.ibm.com> <20120605103055.GA4553@somewhere.redhat.com> <20120605234640.GY2388@linux.vnet.ibm.com> <20120607142101.GI19842@somewhere.redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <20120607142101.GI19842@somewhere.redhat.com> User-Agent: Mutt/1.5.21 (2010-09-15) X-Content-Scanned: Fidelis XPS MAILER x-cbid: 12060804-3534-0000-0000-0000092937BD Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, Jun 07, 2012 at 04:21:09PM +0200, Frederic Weisbecker wrote: > On Tue, Jun 05, 2012 at 04:46:40PM -0700, Paul E. McKenney wrote: > > On Tue, Jun 05, 2012 at 12:31:00PM +0200, Frederic Weisbecker wrote: > > > On Mon, Jun 04, 2012 at 02:07:09PM -0700, Paul E. McKenney wrote: > > > > On Mon, Jun 04, 2012 at 09:06:22PM +0200, Frederic Weisbecker wrote: > > > > > 2012/6/4 Paul E. McKenney : > > > > > > On Mon, Jun 04, 2012 at 02:08:26PM +0200, fweisbec@gmail.com wrote: > > > > > >> From: Frederic Weisbecker > > > > > >> > > > > > >> Paul, Ingo, > > > > > >> > > > > > >> This is a rebase of the nohz cpusets RCU APIs on top of Paul's latest > > > > > >> -rcu (rcu/core) branch. > > > > > >> > > > > > >> I have only built tested it yet, I need to do a full rebase of my > > > > > >> tree to test it in practice. But I wanted to show you how it looks > > > > > >> like first. > > > > > >> > > > > > >> I also wonder if we can set that to a tree somewhere. Ingo suggested > > > > > >> to set up a tree on -tip to apply the uncontroversial part of nohz > > > > > >> cpusets patches and iterate from there. I think it would accelerate > > > > > >> everything if we start doing that. > > > > > > > > > > > > It would probably be best to put these two in the -rcu set in order to > > > > > > avoid conflicts with possible further RCU_FAST_NO_HZ work.  I could > > > > > > push this to -tip early, if that would help. > > > > > > > > > > But then these APIs are going to be upstream on 3.6 > > > > > Is that ok for you even if they don't have any upstream user? > > > > > We can ifdef it. > > > > > > > > I figured on maintaining a separate rcu/idle topic branch that I would > > > > merge locally for building and testing, but which I would not push > > > > to rcu/next. If Ingo agrees, I can push separately to -tip so that it > > > > does not go upstream until you are ready, at which point I would merge > > > > it into rcu/next. > > > > > > > > Seem reasonable, or would something else work better? > > > > > > Sounds very good! > > > > Here you go: > > > > git://git.kernel.org/pub/scm/linux/kernel/git/paulmck/linux-rcu.git rcu/idle > > Thanks! > > I can see you've implemented a version for TinyRCU. Nohz cpusets only work on > SMP right now because there must be at least one CPU running with the tick > to maintain the timekeeping. I'm pretty confident that one day we'll remove > the jiffies and we'll be able to do the whole timekeeping by using the TSC > or so. There is quite a way before we reach that though. In the meantime, would it make sense to slow the tick rate by a factor of 10 or so on that one CPU when nothing else is going on? Or does timekeeping absolutely require running the tick at full speed? Thanx, Paul