From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755451AbbGEJeC (ORCPT ); Sun, 5 Jul 2015 05:34:02 -0400 Received: from e37.co.us.ibm.com ([32.97.110.158]:42308 "EHLO e37.co.us.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755184AbbGEJdv (ORCPT ); Sun, 5 Jul 2015 05:33:51 -0400 X-Helo: d03dlp02.boulder.ibm.com X-MailFrom: paulmck@linux.vnet.ibm.com X-RcptTo: linux-kernel@vger.kernel.org Date: Sat, 4 Jul 2015 21:20:22 -0700 From: "Paul E. McKenney" To: Jean Delvare Cc: LKML Subject: Re: config RCU_EQS_DEBUG Message-ID: <20150705042022.GH3717@linux.vnet.ibm.com> Reply-To: paulmck@linux.vnet.ibm.com References: <20150703100745.7993f403@endymion.delvare> <20150703160037.GV3717@linux.vnet.ibm.com> <20150704185310.616b087b@endymion.delvare> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20150704185310.616b087b@endymion.delvare> User-Agent: Mutt/1.5.21 (2010-09-15) X-TM-AS-MML: disable X-Content-Scanned: Fidelis XPS MAILER x-cbid: 15070504-0025-0000-0000-0000119701AF Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Sat, Jul 04, 2015 at 06:53:10PM +0200, Jean Delvare wrote: > Hi Paul, > > On Fri, 3 Jul 2015 09:00:37 -0700, Paul E. McKenney wrote: > > On Fri, Jul 03, 2015 at 10:07:45AM +0200, Jean Delvare wrote: > > > You just introduced a Linux kernel configuration option named > > > RCU_EQS_DEBUG. Its short description is "Use this when adding any sort > > > of NO_HZ support to your arch". > > > > > > I'm afraid this is a bad way to briefly explain what the option > > > actually does (which is what the short description is for.) A sentence > > > like "use this when adding any sort of NO_HZ support to your arch" > > > should go in the help text, not the short description. The short > > > description should be something like along the lines of "Enable > > > consistency checks for RCU", for example. > > > > > > Additionally I see some inconsistency in the fact that this option > > > defaults to n but the help text says "Say Y if you are unsure". BTW, > > > option RCU_CPU_STALL_INFO is equally inconsistent with a default y and > > > "say N if you are unsure" in the help text. > > > > I have the following queued, which should address your first point. > > Yes it does, thank you. If I were to nitpick I'd say that the option is > adding (or including) the asserts rather than providing them. > > > Would adding "default y" address your other point? > > It would make things consistent, but I have a serious doubt that this > is the right direction. An option which is described as being useful > "when adding any sort of NO_HZ support to a new architecture" really > does not seem to be one that should be enabled by default. You may > argue that it still depends on DEBUG_KERNEL but well, that option is > enabled in pretty much every distribution kernel these days. So I > believe that default n (no default actually) was correct, and what > needs to be removed is the statement "Say Y if you are unsure". If the > user is unsure, then certainly he/she is not working on NO_HZ support > for a new architecture and thus doesn't need to enable RCU_EQS_DEBUG. What would be ideal is if everyone enabled it except for those building systems requiring the fastest possible user-to-kernel switch times. Because it is not that hard to break this even if you don't believe that your are working on NO_HZ support. > > On RCU_CPU_STALL_INFO, I have a patch queued for v4.3 that eliminates > > this Kconfig option completely. > > That solves the problem nicely :-) Glad it works for you! ;-) Thanx, Paul > > rcu: Clarify CONFIG_RCU_EQS_DEBUG help text > > > > Reported-by: Geert Uytterhoeven > > Signed-off-by: Paul E. McKenney > > > > diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug > > index 6be521990d61..80efaade5e59 100644 > > --- a/lib/Kconfig.debug > > +++ b/lib/Kconfig.debug > > @@ -1360,7 +1360,7 @@ config RCU_TRACE > > Say N if you are unsure. > > > > config RCU_EQS_DEBUG > > - bool "Use this when adding any sort of NO_HZ support to your arch" > > + bool "Provide debugging asserts for adding NO_HZ support to an arch" > > depends on DEBUG_KERNEL > > help > > This option provides consistency checks in RCU's handling of > > > > -- > Jean Delvare > SUSE L3 Support >