From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756461AbYJMSCU (ORCPT ); Mon, 13 Oct 2008 14:02:20 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1755277AbYJMSCH (ORCPT ); Mon, 13 Oct 2008 14:02:07 -0400 Received: from fg-out-1718.google.com ([72.14.220.154]:60159 "EHLO fg-out-1718.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755225AbYJMSCG (ORCPT ); Mon, 13 Oct 2008 14:02:06 -0400 Message-ID: <48F38D73.8040804@colorfullife.com> Date: Mon, 13 Oct 2008 20:03:31 +0200 From: Manfred Spraul User-Agent: Thunderbird 2.0.0.16 (X11/20080723) MIME-Version: 1.0 To: paulmck@linux.vnet.ibm.com CC: linux-kernel@vger.kernel.org, cl@linux-foundation.org, mingo@elte.hu, akpm@linux-foundation.org, dipankar@in.ibm.com, josht@linux.vnet.ibm.com, schamp@sgi.com, niv@us.ibm.com, dvhltc@us.ibm.com, ego@in.ibm.com, laijs@cn.fujitsu.com, rostedt@goodmis.org, peterz@infradead.org, penberg@cs.helsinki.fi, andi@firstfloor.org, tglx@linutronix.de Subject: Re: [PATCH, RFC] v7 scalable classic RCU implementation References: <20080821234318.GA1754@linux.vnet.ibm.com> <20080825000738.GA24339@linux.vnet.ibm.com> <20080830004935.GA28548@linux.vnet.ibm.com> <20080905152930.GA8124@linux.vnet.ibm.com> <20080915160221.GA9660@linux.vnet.ibm.com> <20080923235340.GA12166@linux.vnet.ibm.com> <20081010160930.GA9777@linux.vnet.ibm.com> <48F21D58.3000404@colorfullife.com> <20081012224629.GA7353@linux.vnet.ibm.com> In-Reply-To: <20081012224629.GA7353@linux.vnet.ibm.com> Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Paul E. McKenney wrote: > Do you send a reschedule IPI to CPUs that are not in dyntick idle mode, > but who have failed to pass through a quiescent state? > Actually, I never send reschedule IPIs. - For "usual" cpus, rcu_check_callbacks() checks for quiescent states. There should be a set_need_resched() if a cpu holds up a grace period for too long. I just haven't implemented it yet. IMHO it doesn't make sense to perform a "for_each_cpu() smd_send_reschedule()". rcu has a hook in each cpu, thus a set_need_resched() by the per-cpu hook is faster/simpler. - For nohz cpus, a poller function [schedule_work(), enabled interrupts] peeks into the per-cpu data of the nohz cpu and checks if it is quiet or if it passed through a quiescent state. If it didn't, then it sets a cpu_data->kick_poller flag and rcu_irq_exit() reports the grace period. No need for an IPI either - rcu has a hook in the irq exit path. Right now, I cheat if a nohz cpu is in a long-running nmi [while(other_cpu_is_in_nmi()) cpu_relax()], but I think I can fix that with an set_need_resched() in the rcu_nmi_exit(). -- Manfred