From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751708Ab1EYEw5 (ORCPT ); Wed, 25 May 2011 00:52:57 -0400 Received: from e8.ny.us.ibm.com ([32.97.182.138]:59756 "EHLO e8.ny.us.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750805Ab1EYEw4 (ORCPT ); Wed, 25 May 2011 00:52:56 -0400 Date: Tue, 24 May 2011 21:52:53 -0700 From: "Paul E. McKenney" To: Yinghai Lu 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" Message-ID: <20110525045253.GB2262@linux.vnet.ibm.com> Reply-To: paulmck@linux.vnet.ibm.com 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> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <4DDC48E3.1060108@kernel.org> User-Agent: Mutt/1.5.20 (2009-06-14) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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. Thanx, Paul