From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752499Ab1KCNds (ORCPT ); Thu, 3 Nov 2011 09:33:48 -0400 Received: from e3.ny.us.ibm.com ([32.97.182.143]:37184 "EHLO e3.ny.us.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751177Ab1KCNdr (ORCPT ); Thu, 3 Nov 2011 09:33:47 -0400 Date: Thu, 3 Nov 2011 06:32:31 -0700 From: "Paul E. McKenney" To: Frederic Weisbecker Cc: Josh Triplett , 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, eric.dumazet@gmail.com, darren@dvhart.com, patches@linaro.org, Mike Frysinger , Guan Xuetao , David Miller , Chris Metcalf , Hans-Christian Egtvedt , Ralf Baechle , Ingo Molnar , Peter Zijlstra , "H. Peter Anvin" , Russell King , Paul Mackerras , Heiko Carstens , Paul Mundt Subject: Re: [PATCH RFC tip/core/rcu 19/28] nohz: Allow rcu extended quiescent state handling seperately from tick stop Message-ID: <20111103133231.GA2287@linux.vnet.ibm.com> Reply-To: paulmck@linux.vnet.ibm.com References: <20111102203017.GA3830@linux.vnet.ibm.com> <1320265849-5744-19-git-send-email-paulmck@linux.vnet.ibm.com> <20111103040003.GE2042@leaf> <20111103115426.GD8198@somewhere.redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20111103115426.GD8198@somewhere.redhat.com> User-Agent: Mutt/1.5.20 (2009-06-14) x-cbid: 11110313-8974-0000-0000-000001631663 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, Nov 03, 2011 at 12:54:33PM +0100, Frederic Weisbecker wrote: > On Wed, Nov 02, 2011 at 09:00:03PM -0700, Josh Triplett wrote: > > On Wed, Nov 02, 2011 at 01:30:40PM -0700, Paul E. McKenney wrote: > > > From: Frederic Weisbecker > > > > > > It is assumed that rcu won't be used once we switch to tickless > > > mode and until we restart the tick. However this is not always > > > true, as in x86-64 where we dereference the idle notifiers after > > > the tick is stopped. > > > > > > To prepare for fixing this, add two new APIs: > > > tick_nohz_idle_enter_norcu() and tick_nohz_idle_exit_norcu(). > > > > > > If no use of RCU is made in the idle loop between > > > tick_nohz_enter_idle() and tick_nohz_exit_idle() calls, the arch > > > must instead call the new *_norcu() version such that the arch doesn't > > > need to call rcu_idle_enter() and rcu_idle_exit(). > > > > The _norcu names confused me a bit. At first, I thought they meant > > "idle but not RCU idle, so you can use RCU", but from re-reading the > > commit message, apparently they mean "idle and RCU idle, so don't use > > RCU". What about something like _forbid_rcu instead? Or, > > alternatively, why not just go ahead and separate the two types of idle > > entirely rather than introducing the _norcu variants first? > > Or tick_nohz_idle_enter_rcu_stop() and tick_nohz_idle_exit_rcu_restart()? > > Sounds clear but too long. May be we can shorten the tick_nohz thing in the > beginning. How about tick_nohz_rcu_idle_enter() vs. tick_nohz_idle_enter() on entry to the idle loop and tick_nohz_rcu_idle_exit() vs tick_nohz_idle_exit() on exit? That said, I don't feel all that strongly on this naming topic. Thanx, Paul