From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753403Ab3AGRNL (ORCPT ); Mon, 7 Jan 2013 12:13:11 -0500 Received: from slow3-v.mail.gandi.net ([217.70.178.89]:44912 "EHLO slow3-v.mail.gandi.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751467Ab3AGRNJ (ORCPT ); Mon, 7 Jan 2013 12:13:09 -0500 X-Greylist: delayed 1206 seconds by postgrey-1.27 at vger.kernel.org; Mon, 07 Jan 2013 12:13:09 EST X-Policy: 217.70.183.197 is whitelisted X-Policy: 217.70.183.197 is whitelisted X-Originating-IP: 217.70.178.138 X-Originating-IP: 50.43.39.152 Date: Mon, 7 Jan 2013 08:50:23 -0800 From: Josh Triplett To: "Paul E. McKenney" Cc: linux-kernel@vger.kernel.org, mingo@elte.hu, laijs@cn.fujitsu.com, dipankar@in.ibm.com, akpm@linux-foundation.org, mathieu.desnoyers@polymtl.ca, niv@us.ibm.com, tglx@linutronix.de, peterz@infradead.org, rostedt@goodmis.org, Valdis.Kletnieks@vt.edu, dhowells@redhat.com, edumazet@google.com, darren@dvhart.com, fweisbec@gmail.com, sbw@mit.edu, patches@linaro.org, "Paul E. McKenney" Subject: Re: [PATCH tip/core/rcu 04/14] rcu: Provide compile-time control for no-CBs CPUs Message-ID: <20130107165023.GA12229@leaf> References: <20130105174844.GA14172@linux.vnet.ibm.com> <1357408144-15830-1-git-send-email-paulmck@linux.vnet.ibm.com> <1357408144-15830-4-git-send-email-paulmck@linux.vnet.ibm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1357408144-15830-4-git-send-email-paulmck@linux.vnet.ibm.com> User-Agent: Mutt/1.5.21 (2010-09-15) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Sat, Jan 05, 2013 at 09:48:54AM -0800, Paul E. McKenney wrote: > From: "Paul E. McKenney" > > Currently, the only way to specify no-CBs CPUs is via the rcu_nocbs > kernel command-line parameter. This is inconvenient in some cases, > particularly for randconfig testing, so this commit adds a new > RCU_NOCB_CPU_DEFAULT kernel configuration parameter. Setting this > new parameter to zero (the default) retains the old behavior, setting > it to one offloads callback processing from CPU 0 (along with any > other CPUs specified by the rcu_nocbs boot-time parameter), and setting > it to two offloads callback processing from all CPUs. > > Signed-off-by: Paul E. McKenney > Signed-off-by: Paul E. McKenney Comments below. > init/Kconfig | 13 +++++++++++++ > kernel/rcutree_plugin.h | 13 +++++++++++++ > 2 files changed, 26 insertions(+), 0 deletions(-) > > diff --git a/init/Kconfig b/init/Kconfig > index fc6a3ca..35dcedb 100644 > --- a/init/Kconfig > +++ b/init/Kconfig > @@ -676,6 +676,19 @@ config RCU_NOCB_CPU > Say Y here if you want to help to debug reduced OS jitter. > Say N here if you are unsure. > > +config RCU_NOCB_CPU_DEFAULT > + int "Offload RCU callback processing from compile-selected CPUs" > + depends on RCU_NOCB_CPU > + range 0 2 > + default 0 > + help > + Set this option to zero to only offload RCU callback processing > + from those CPUs specified by the boot-time rcu_nocbs kernel > + parameter. Set it to one to offload processing from CPU 0 > + in addition to any CPUs specified at boot time. Set it to > + two to offload processing from all CPUs, regardless of the > + setting of the boot-time rcu_nocbs kernel parameter. > + Rather than making users translate the meanings of 0, 1, and 2, this seems like something better done with a choice/endchoice; that would then offer a menu of options that can each have their own description. Take a look at the "Memory split" option in arch/x86/Kconfig for an example. > --- a/kernel/rcutree_plugin.h > +++ b/kernel/rcutree_plugin.h > @@ -86,6 +86,19 @@ static void __init rcu_bootup_announce_oddness(void) > if (nr_cpu_ids != NR_CPUS) > printk(KERN_INFO "\tRCU restricting CPUs from NR_CPUS=%d to nr_cpu_ids=%d.\n", NR_CPUS, nr_cpu_ids); > #ifdef CONFIG_RCU_NOCB_CPU > +#if CONFIG_RCU_NOCB_CPU_DEFAULT != 0 That would then make each of these conditionals self-documenting as well. - Josh Triplett