From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753196AbZIEUBq (ORCPT ); Sat, 5 Sep 2009 16:01:46 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1753092AbZIEUBp (ORCPT ); Sat, 5 Sep 2009 16:01:45 -0400 Received: from e6.ny.us.ibm.com ([32.97.182.146]:36117 "EHLO e6.ny.us.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752897AbZIEUBo (ORCPT ); Sat, 5 Sep 2009 16:01:44 -0400 Date: Sat, 5 Sep 2009 13:01:46 -0700 From: "Paul E. McKenney" To: Valdis.Kletnieks@vt.edu Cc: Andrew Morton , linux-kernel@vger.kernel.org Subject: Re: RCU Kconfig help text Message-ID: <20090905200145.GB7181@linux.vnet.ibm.com> Reply-To: paulmck@linux.vnet.ibm.com References: <12924.1252157230@turing-police.cc.vt.edu> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <12924.1252157230@turing-police.cc.vt.edu> 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 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. Thanx, Paul