From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756825Ab1EYWQQ (ORCPT ); Wed, 25 May 2011 18:16:16 -0400 Received: from rcsinet10.oracle.com ([148.87.113.121]:51052 "EHLO rcsinet10.oracle.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753558Ab1EYWQP (ORCPT ); Wed, 25 May 2011 18:16:15 -0400 Message-ID: <4DDD7F96.3090408@kernel.org> Date: Wed, 25 May 2011 15:15:50 -0700 From: Yinghai Lu User-Agent: Mozilla/5.0 (X11; U; Linux x86_64; en-US; rv:1.9.2.17) Gecko/20110414 SUSE/3.1.10 Thunderbird/3.1.10 MIME-Version: 1.0 To: paulmck@linux.vnet.ibm.com CC: linux-kernel@vger.kernel.org, mingo@redhat.com, hpa@zytor.com, tglx@linutronix.de, mingo@elte.hu Subject: Re: [tip:core/rcu] Revert "rcu: Decrease memory-barrier usage based on semi-formal proof" References: <4DDAC01E.7050602@kernel.org> <20110523212530.GF7428@linux.vnet.ibm.com> <4DDAD934.9010603@kernel.org> <4DDAE5FA.2030303@kernel.org> <4DDAE6A5.6060701@kernel.org> <20110524011824.GL7428@linux.vnet.ibm.com> <4DDB093F.2060601@kernel.org> <20110524013523.GO7428@linux.vnet.ibm.com> <4DDC21E1.1070502@kernel.org> <4DDC48E3.1060108@kernel.org> <20110525045253.GB2262@linux.vnet.ibm.com> In-Reply-To: <20110525045253.GB2262@linux.vnet.ibm.com> Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit X-Source-IP: rtcsinet21.oracle.com [66.248.204.29] X-CT-RefId: str=0001.0A090205.4DDD7F9C.00AF,ss=1,fgs=0 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 05/24/2011 09:52 PM, Paul E. McKenney wrote: > On Tue, May 24, 2011 at 05:10:11PM -0700, Yinghai Lu wrote: >> On 05/24/2011 02:23 PM, Yinghai Lu wrote: >>> On 05/23/2011 06:35 PM, Paul E. McKenney wrote: >>>> On Mon, May 23, 2011 at 06:26:23PM -0700, Yinghai Lu wrote: >>>>> On 05/23/2011 06:18 PM, Paul E. McKenney wrote: >>>>> >>>>>> OK, so it looks like I need to get this out of the way in order to track >>>>>> down the delays. Or does reverting PeterZ's patch get you a stable >>>>>> system, but with the longish delays in memory_dev_init()? If the latter, >>>>>> it might be more productive to handle the two problems separately. >>>>>> >>>>>> For whatever it is worth, I do see about 5% increase in grace-period >>>>>> duration when switching to kthreads. This is acceptable -- your >>>>>> 30x increase clearly is completely unacceptable and must be fixed. >>>>>> Other than that, the main thing that affects grace period duration is >>>>>> the setting of CONFIG_HZ -- the smaller the HZ value, the longer the >>>>>> grace-period duration. >>>>> >>>>> for my 1024g system when memory hotadd is enabled in kernel config: >>>>> 1. current linus tree + tip tree: memory_dev_init will take about 100s. >>>>> 2. current linus tree + tip tree + your tree - Peterz patch: >>>>> a. on fedora 14 gcc: will cost about 4s: like old times >>>>> b. on opensuse 11.3 gcc: will cost about 10s. >>>> >>>> So some patch in my tree that is not yet in tip makes things better? >>>> >>>> If so, could you please see which one? Maybe that would give me a hint >>>> that could make things better on opensuse 11.3 as well. >>> >>> today's tip: >>> >>> [ 31.795597] cpu_dev_init done >>> [ 40.930202] memory_dev_init done >>> >> >> another boot from tip got: >> >> [ 35.211927] cpu_dev_init done >> [ 136.053698] memory_dev_init done >> >> wonder if you can have clean revert for >> >> commit a26ac2455ffcf3be5c6ef92bc6df7182700f2114 >>> Author: Paul E. McKenney >>> Date: Wed Jan 12 14:10:23 2011 -0800 >>> >>> rcu: move TREE_RCU from softirq to kthread >>> >>> If RCU priority boosting is to be meaningful, callback invocation must >>> be boosted in addition to preempted RCU readers. Otherwise, in presence >>> of CPU real-time threads, the grace period ends, but the callbacks don't >>> get invoked. If the callbacks don't get invoked, the associated memory >>> doesn't get freed, so the system is still subject to OOM. >>> >>> But it is not reasonable to priority-boost RCU_SOFTIRQ, so this commit >>> moves the callback invocations to a kthread, which can be boosted easily. >>> >>> Also add comments and properly synchronized all accesses to >>> rcu_cpu_kthread_task, as suggested by Lai Jiangshan. >>> >>> Signed-off-by: Paul E. McKenney >>> Signed-off-by: Paul E. McKenney >>> Reviewed-by: Josh Triplett > > There is a new branch yinghai.2011.05.24a on: > > git://git.kernel.org/pub/scm/linux/kernel/git/paulmck/linux-2.6-rcu.git > > Or will be as soon as kernel.org updates its mirrors. > > I am not sure I could call this "clean", but it does revert that commit > and 11 of the subsequent commits that depend on it. It does build, > and I will test it once my currently running tests complete. yes, with those revert, there is no delay in 10 times booting. Thanks Yinghai