From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755836Ab3AGWJ6 (ORCPT ); Mon, 7 Jan 2013 17:09:58 -0500 Received: from e36.co.us.ibm.com ([32.97.110.154]:51554 "EHLO e36.co.us.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754563Ab3AGWJ5 (ORCPT ); Mon, 7 Jan 2013 17:09:57 -0500 Date: Mon, 7 Jan 2013 14:09:43 -0800 From: "Paul E. McKenney" To: Josh Triplett 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: <20130107220943.GY2525@linux.vnet.ibm.com> Reply-To: paulmck@linux.vnet.ibm.com 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> <20130107165023.GA12229@leaf> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20130107165023.GA12229@leaf> User-Agent: Mutt/1.5.21 (2010-09-15) X-Content-Scanned: Fidelis XPS MAILER x-cbid: 13010722-7606-0000-0000-000007396F3C Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, Jan 07, 2013 at 08:50:23AM -0800, Josh Triplett wrote: > 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. My first reaction was that this couldn't possibly handle the dependency on CONFIG_RCU_NOCB_CPU, but it actually does work, suppressing all the choices when CONFIG_RCU_NOCB_CPU=n. Cute! > > --- 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. Indeed, much better! Thank you! Thanx, Paul