From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1757281Ab0HIWPa (ORCPT ); Mon, 9 Aug 2010 18:15:30 -0400 Received: from e2.ny.us.ibm.com ([32.97.182.142]:49295 "EHLO e2.ny.us.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1757189Ab0HIWPV (ORCPT ); Mon, 9 Aug 2010 18:15:21 -0400 From: "Paul E. McKenney" To: linux-kernel@vger.kernel.org Cc: mingo@elte.hu, laijs@cn.fujitsu.com, dipankar@in.ibm.com, akpm@linux-foundation.org, mathieu.desnoyers@polymtl.ca, 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, eric.dumazet@gmail.com, "Paul E. McKenney" Subject: [PATCH tip/core/rcu 07/10] rcu: Fix RCU_FANOUT help message Date: Mon, 9 Aug 2010 15:15:08 -0700 Message-Id: <1281392111-25060-7-git-send-email-paulmck@linux.vnet.ibm.com> X-Mailer: git-send-email 1.7.0.6 In-Reply-To: <20100809221447.GA24358@linux.vnet.ibm.com> References: <20100809221447.GA24358@linux.vnet.ibm.com> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Commit cf244dc01bf68 added a fourth level to the TREE_RCU hierarchy, but the RCU_FANOUT help message still said "cube root". This commit fixes this to "fourth root" and also emphasizes that production systems are well-served by the default. (Stress-testing RCU itself uses small RCU_FANOUT values in order to test large-system code paths on small(er) systems.) Located-by: John Kacur Signed-off-by: Paul E. McKenney --- init/Kconfig | 9 ++++++--- 1 files changed, 6 insertions(+), 3 deletions(-) diff --git a/init/Kconfig b/init/Kconfig index 9366954..7faa5d8 100644 --- a/init/Kconfig +++ b/init/Kconfig @@ -384,9 +384,12 @@ config RCU_FANOUT help This option controls the fanout of hierarchical implementations of RCU, allowing RCU to work efficiently on machines with - large numbers of CPUs. This value must be at least the cube - root of NR_CPUS, which allows NR_CPUS up to 32,768 for 32-bit - systems and up to 262,144 for 64-bit systems. + large numbers of CPUs. This value must be at least the fourth + root of NR_CPUS, which allows NR_CPUS to be insanely large. + The default value of RCU_FANOUT should be used for production + systems, but if you are stress-testing the RCU implementation + itself, small RCU_FANOUT values allow you to test large-system + code paths on small(er) systems. Select a specific number if testing RCU itself. Take the default if unsure. -- 1.7.0.6