From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753611Ab0A0FVj (ORCPT ); Wed, 27 Jan 2010 00:21:39 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1750991Ab0A0FVh (ORCPT ); Wed, 27 Jan 2010 00:21:37 -0500 Received: from e9.ny.us.ibm.com ([32.97.182.139]:46493 "EHLO e9.ny.us.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750870Ab0A0FVh (ORCPT ); Wed, 27 Jan 2010 00:21:37 -0500 Date: Tue, 26 Jan 2010 21:21:33 -0800 From: "Paul E. McKenney" To: Mathieu Desnoyers Cc: Andi Kleen , linux-kernel@vger.kernel.org, mingo@elte.hu, laijs@cn.fujitsu.com, dipankar@in.ibm.com, akpm@linux-foundation.org, josh@joshtriplett.org, dvhltc@us.ibm.com, niv@us.ibm.com, tglx@linutronix.de, peterz@infradead.org, rostedt@goodmis.org, Valdis.Kletnieks@vt.edu, dhowells@redhat.com Subject: Re: [PATCH RFC tip/core/rcu] accelerate grace period if last non-dynticked CPU Message-ID: <20100127052133.GD6807@linux.vnet.ibm.com> Reply-To: paulmck@linux.vnet.ibm.com References: <20100125034816.GA14043@linux.vnet.ibm.com> <873a1sft9q.fsf@basil.nowhere.org> <20100126235516.GA15855@Krystal> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20100126235516.GA15855@Krystal> User-Agent: Mutt/1.5.15+20070412 (2007-04-11) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, Jan 26, 2010 at 06:55:16PM -0500, Mathieu Desnoyers wrote: > * Andi Kleen (andi@firstfloor.org) wrote: > > "Paul E. McKenney" writes: > > > > Kind of offtopic to the original patch, but I couldn't > > resist... > > > > > +config RCU_FAST_NO_HZ > > > + bool "Accelerate last non-dyntick-idle CPU's grace periods" > > > + depends on TREE_RCU && NO_HZ && SMP > > > > Having such a thing as a config option doesn't really make > > any sense to me. Who would want to recompile their kernel > > to enable/disable this? If anything it should be runtime, or better > > just unconditionally on. > > > > In general RCU could probably reduce its number of "weird" > > Kconfig options. > > > > While I think I have a better understanding of RCU than a lot > > of normal users I often have no clue what to set there when > > building a kernel. > > Maybe we could keep them under a CONFIG_DEBUG_RCU umbrella. Compiling > out parts of the rcu options can be useful for debugging purposes, but > I agree with you that end users should not be bothered with that much > options when some of them are "obviously" wanted. > > OTOH, I understand that Paul seems to want to introduce new RCU > features gradually, without hitting all kernel users with bugs in newer > features. That's a sane approach to keep things generally stable, but > maybe it is time to set some of the stabilized RCU options to default Y > and move their config to the debug menu. That is indeed a big part of the motivation. ;-) Thanx, Paul > Let's see what Paul has to say about this... > > Thanks, > > Mathieu > > > > > -Andi > > > > -- > > ak@linux.intel.com -- Speaking for myself only. > > -- > Mathieu Desnoyers > OpenPGP key fingerprint: 8CD5 52C3 8E3C 4140 715F BA06 3F25 A8FE 3BAE 9A68