From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754406AbZIFGZM (ORCPT ); Sun, 6 Sep 2009 02:25:12 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1754320AbZIFGZL (ORCPT ); Sun, 6 Sep 2009 02:25:11 -0400 Received: from atrey.karlin.mff.cuni.cz ([195.113.26.193]:54332 "EHLO atrey.karlin.mff.cuni.cz" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754303AbZIFGZK (ORCPT ); Sun, 6 Sep 2009 02:25:10 -0400 Date: Sun, 6 Sep 2009 08:24:41 +0200 From: Pavel Machek To: "Paul E. McKenney" Cc: Valdis.Kletnieks@vt.edu, Andrew Morton , linux-kernel@vger.kernel.org Subject: Re: RCU Kconfig help text Message-ID: <20090906062441.GD1431@ucw.cz> References: <12924.1252157230@turing-police.cc.vt.edu> <20090905200145.GB7181@linux.vnet.ibm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20090905200145.GB7181@linux.vnet.ibm.com> User-Agent: Mutt/1.5.18 (2008-05-17) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Sat 2009-09-05 13:01:46, Paul E. McKenney wrote: > On Sat, Sep 05, 2009 at 09:27:10AM -0400, Valdis.Kletnieks@vt.edu wrote: > > init/Kconfig says: > > > > "choice > > prompt "RCU Implementation" > > default TREE_RCU > > > > config TREE_RCU > > bool "Tree-based hierarchical RCU" > > help > > This option selects the RCU implementation that is > > designed for very large SMP system with hundreds or > > thousands of CPUs. It also scales down nicely to > > smaller systems. > > > > config TREE_PREEMPT_RCU > > bool "Preemptable tree-based hierarchical RCU" > > depends on PREEMPT > > help > > This option selects the RCU implementation that is > > designed for very large SMP systems with hundreds or > > thousands of CPUs, but for which real-time response > > is also required. > > > > endchoice" > > > > This leaves somebody who has a laptop wondering which choice is best for > > a system with only one or two cores that has CONFIG_PREEMPT defined. One > > choice says it scales down nicely, the other explicitly has a 'depends on > > PREEMPT' attached to it... > > > > (Yes, I realize in practice, the RCU sections on a laptop are probably usually > > so short they don't matter in practice. I finally concluded TREE_PREEMPT was > > apparently a rename of CONFIG_PREEMPT_RCU and went with that since that was > > working for me before...) > > Good point -- I will add the "It also scales down nicely to smaller > systems" to TREE_PREEMPT_RCU. > > For -really- small systems, TINY_RCU will hopefully be there at some > point, but it can only handle single-CPU systems. If so, call it 'UP_RCU' or 'UNIPROCESSOR_RCU'? Pavel -- (english) http://www.livejournal.com/~pavelmachek (cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html