Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S935205Ab3DKR2O (ORCPT ); Thu, 11 Apr 2013 13:28:14 -0400 Received: from mail-qc0-f177.google.com ([209.85.216.177]:42875 "EHLO mail-qc0-f177.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753176Ab3DKR2N (ORCPT ); Thu, 11 Apr 2013 13:28:13 -0400 Date: Thu, 11 Apr 2013 19:28:05 +0200 From: Frederic Weisbecker To: "Paul E. McKenney" Cc: Christoph Lameter , Ingo Molnar , LKML , Andrew Morton , Chris Metcalf , Geoff Levand , Gilad Ben Yossef , Hakan Akkan , Kevin Hilman , Li Zhong , Namhyung Kim , Paul Gortmaker , Peter Zijlstra , Steven Rostedt , Thomas Gleixner Subject: Re: [PATCH 4/4] nohz: New option to force all CPUs in full dynticks range Message-ID: <20130411172803.GC17129@somewhere.redhat.com> References: <20130328074507.GC24433@gmail.com> <20130330091037.GA31743@gmail.com> <0000013dea26b171-8095c339-dc81-4459-a3ad-a8d69c803448-000000@email.amazonses.com> <20130411151956.GF15699@somewhere> <20130411153721.GA3742@linux.vnet.ibm.com> <20130411155349.GA16797@somewhere.redhat.com> <0000013df9f8d526-2783fba3-4dc9-44c6-8b02-2c321eb5b37b-000000@email.amazonses.com> <20130411170420.GA17129@somewhere.redhat.com> <20130411171153.GG29861@linux.vnet.ibm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20130411171153.GG29861@linux.vnet.ibm.com> User-Agent: Mutt/1.5.21 (2010-09-15) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1966 Lines: 46 On Thu, Apr 11, 2013 at 10:11:53AM -0700, Paul E. McKenney wrote: > On Thu, Apr 11, 2013 at 07:04:23PM +0200, Frederic Weisbecker wrote: > > On Thu, Apr 11, 2013 at 04:41:07PM +0000, Christoph Lameter wrote: > > > On Thu, 11 Apr 2013, Frederic Weisbecker wrote: > > > > > > > If there is no performance issue with that I'm all for it. > > > > > > Or have a > > > > > > CONFIG_LOWLATENCY > > > > > > that boots up a kernel with the proper configuration? > > > > It may be too general for a naming. But I don't mind just > > selecting CONFIG_RCU_NOCBS_ALL unconditionally. It's easily > > changed in the future if anybody complains. > > > > Btw, if CONFIG_RCU_NOCBS_ALL is set, the rcu_nocbs= parameter > > is ignored, right? If you want to keep that direction and not > > override the Kconfig choice, may be warn the user about that > > if the boot parameter is passed? > > Fair point. Let me think about how I should approach Thanx. An alternative is to treat the Kconfig choice as a default setting that gets overriden by rcu_nocbs= This would require to refactor the three way Kconfig layout you've set, but that aligns with what Ingo is suggesting me to do with the full dynticks range: having CONFIG_NO_HZ_EXTENDED_ALL that is overriden by nohz_extended= if any (beware though, "extended" will soon be renamed to "full", lets hope it's our last take ;) That unifies both behaviours and it looks more flexible to me. Of course that means selecting CONFIG_RCU_NOCBS_ALL won't be enough for me to ensure my nohz range is also nocb, I'm fine with the cpumask check on boot though. Anyway, that's just a suggestion, the most important is that the user is informed of what's happening and how to deal with it. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/