From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1758778AbZDWIHR (ORCPT ); Thu, 23 Apr 2009 04:07:17 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1760098AbZDWHzG (ORCPT ); Thu, 23 Apr 2009 03:55:06 -0400 Received: from mx3.mail.elte.hu ([157.181.1.138]:40693 "EHLO mx3.mail.elte.hu" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1760081AbZDWHzE (ORCPT ); Thu, 23 Apr 2009 03:55:04 -0400 Date: Thu, 23 Apr 2009 09:54:36 +0200 From: Ingo Molnar To: "Paul E. McKenney" Cc: linux-kernel@vger.kernel.org, netdev@vger.kernel.org, netfilter-devel@vger.kernel.org, akpm@linux-foundation.org, torvalds@linux-foundation.org, davem@davemloft.net, dada1@cosmosbay.com, zbr@ioremap.net, jeff.chua.linux@gmail.com, paulus@samba.org, laijs@cn.fujitsu.com, jengelh@medozas.de, r000n@r000n.net, benh@kernel.crashing.org, mathieu.desnoyers@polymtl.ca Subject: Re: [PATCH RFC] v1 expedited "big hammer" RCU grace periods Message-ID: <20090423075436.GB22606@elte.hu> References: <20090423052520.GA13036@linux.vnet.ibm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20090423052520.GA13036@linux.vnet.ibm.com> User-Agent: Mutt/1.5.18 (2008-05-17) X-ELTE-VirusStatus: clean X-ELTE-SpamScore: -1.5 X-ELTE-SpamLevel: X-ELTE-SpamCheck: no X-ELTE-SpamVersion: ELTE 2.0 X-ELTE-SpamCheck-Details: score=-1.5 required=5.9 tests=BAYES_00 autolearn=no SpamAssassin version=3.2.5 -1.5 BAYES_00 BODY: Bayesian spam probability is 0 to 1% [score: 0.0000] Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org * Paul E. McKenney wrote: > First cut of "big hammer" expedited RCU grace periods, but only > for rcu_bh. This creates another softirq vector, so that entering > this softirq vector will have forced an rcu_bh quiescent state (as > noted by Dave Miller). Use smp_call_function() to invoke > raise_softirq() on all CPUs in order to cause this to happen. > Track the CPUs that have passed through a quiescent state (or gone > offline) with a cpumask. > > Does nothing to expedite callbacks already registered with > call_rcu_bh(), but there is no need to. > > Shortcomings: > > o Untested, probably does not compile, not for inclusion. > > o Does not handle rcu, only rcu_bh. > > Thoughts? I'm wondering, why not just do a two-liner, along the lines of: for_each_online_cpu(cpu) smp_send_reschedule(cpu); That should trigger a quiescent state on all online cpus. It wont perturb the scheduler state (which is reschedule-IPI invariant). (And this is a big-hammer approach anyway so even if it did we wouldnt care.) Am i missing something embarrasingly obvious perhaps? Ingo