Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752878AbYJ1F21 (ORCPT ); Tue, 28 Oct 2008 01:28:27 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1752147AbYJ1F2T (ORCPT ); Tue, 28 Oct 2008 01:28:19 -0400 Received: from fk-out-0910.google.com ([209.85.128.184]:55595 "EHLO fk-out-0910.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752124AbYJ1F2S (ORCPT ); Tue, 28 Oct 2008 01:28:18 -0400 Message-ID: <4906A370.3000502@colorfullife.com> Date: Tue, 28 Oct 2008 06:30:24 +0100 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: <20081012224629.GA7353@linux.vnet.ibm.com> <48F38D73.8040804@colorfullife.com> <20081015011143.GE6874@linux.vnet.ibm.com> <48F5A638.8020003@colorfullife.com> <20081015152637.GA6739@linux.vnet.ibm.com> <48FF73C7.90709@colorfullife.com> <20081022210254.GE6766@linux.vnet.ibm.com> <48FF9A0E.90205@colorfullife.com> <20081027164529.GC6783@linux.vnet.ibm.com> <49061AF0.8070106@colorfullife.com> <20081027235201.GK6783@linux.vnet.ibm.com> In-Reply-To: <20081027235201.GK6783@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 Content-Length: 3096 Lines: 75 Paul E. McKenney wrote: > On Mon, Oct 27, 2008 at 08:48:00PM +0100, Manfred Spraul wrote: > >> Paul E. McKenney wrote: >> >>> Agreed. Perhaps a good change to make while introducing stall detection >>> to preemptable RCU -- there would then be three examples, which should >>> allow good generalization. >>> >>> >> Two implementations. IMHO the current rcu-classic code should be dropped >> immediately when you add rcu-tree: >> rcu-classic is buggy, as far as I can see long-running interrupts on nohz >> cpus are not handled correctly. I don't think it makes sense to keep it in >> the kernel in parallel to rcu-tree. >> >> I would propose that rcu-tree replaces rcu-classic. >> I'll continue to update rcu-state, I think that it will achieve lower >> latency than rcu-tree [average/max time between call_rcu() and destruction >> callback] and it doesn't have the irq disabled loop to find the missing >> cpus. >> If I find decent benchmarks where I can quantify the advantages, then I'll >> propose to merge rcu-state as a third implementation in addition to >> rcu-tree and rcu-preempt. >> >> Paul: What do you think? >> > > In keeping with my reputation as a "conservative programmer", I would > suggest that rcuclassic.c remain for a year or so. Distros branching > off during this time should continue making rcuclassic.c be the default. > Other uses should have rcutree.c as the default. At the end of the year, > we remove rcuclassic.c. > > All that said, one attractive aspect of your suggestion is immediately > removing rcuclassic.c would eliminate the need to do further work on it. ;-) > > How do you intend to handle nohz cpus? I would create a separate patch that removes rcuclassic.c. distros that want to keep rcuclassic could just revert that change. -- Manfred > Your benchmarking proposal for rcu-state makes sense to me. > > One other possible place for techniques from rcu-state may be in making > preemptable RCU scale. This may take some time, as other parts of > the RT kernel have their limitations, but sooner or later people are > going to expect real-time response from even the largest machines. > In addition, preemptable RCU has a number of shorter-term issues: > > 1. RCU-boosting mechanism. (I need to combine the best of > Steve's and my mechanisms. The treercu.c effort has been > sort of a warm-up exercise for RCU-boosting.) > > 2. Reducing the latency contribution of the preemptable RCU > state machine (but note that moving this state machine out > of the scheduling-clock irq handler means more stuff to boost). > > 3. Porting the simpler dynticks interface from rcutree to > preemptable RCU. > > 4. Making the preemptable RCU tracing code use seqfile. > > Hmmm... Maybe it is (past) time for me to publish an RCU to-do list? > > Thanx, Paul > -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/