Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754118Ab3DOK14 (ORCPT ); Mon, 15 Apr 2013 06:27:56 -0400 Received: from mail-ea0-f182.google.com ([209.85.215.182]:52823 "EHLO mail-ea0-f182.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752467Ab3DOK1y (ORCPT ); Mon, 15 Apr 2013 06:27:54 -0400 Date: Mon, 15 Apr 2013 12:27:50 +0200 From: Ingo Molnar To: Christoph Lameter Cc: Frederic Weisbecker , "Paul E. McKenney" , 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: <20130415102750.GE18024@gmail.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> <0000013dfef98b2d-ed5980b1-86ff-47de-8aa1-fd7fdd02f034-000000@email.amazonses.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <0000013dfef98b2d-ed5980b1-86ff-47de-8aa1-fd7fdd02f034-000000@email.amazonses.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: 1925 Lines: 47 * Christoph Lameter wrote: > On Thu, 11 Apr 2013, Frederic Weisbecker wrote: > > > 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. > > > I like the general nature of that config option since it removes the need to > configure all the details. For an average user the current sets of options must > look pretty complicated. Yes. It's not just complicated but also fragile and time consuming: as new kernel options arrive you'd always have to be very careful with 'make oldconfig' and make sure you pick up the best options for latency. Instead what we want is generally a high level knob that documents user preference and then the kernel config language can do the rest. > > > Btw, if CONFIG_RCU_NOCBS_ALL isset, 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? > > Ok. But all these complicated things would go away if we had an option > CONFIG_LOWLATENCY and then everything would just follow the best setup > possible given the hardware. Would remove a lot of guesswork and a lot of > knobs. In that sense CONFIG_NO_HZ_FULL is such a flag as well, which, like CONFIG_PREEMPT_RT, tries to preconfigure the kernel correctly. But we have to be careful not to use a too highlevel flag for that. If the user meant 'low latency' to mean 'low latency IRQ execution' - then enabling CONFIG_NO_HZ_FULL might achieve the opposite, it adds overhead to the IRQ paths. Thanks, Ingo -- 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/