Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752694AbYK0Jke (ORCPT ); Thu, 27 Nov 2008 04:40:34 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1752599AbYK0Jj5 (ORCPT ); Thu, 27 Nov 2008 04:39:57 -0500 Received: from bombadil.infradead.org ([18.85.46.34]:44813 "EHLO bombadil.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752440AbYK0Jjw (ORCPT ); Thu, 27 Nov 2008 04:39:52 -0500 Subject: Re: [PATCH 4/6] fs: Introduce a per_cpu nr_inodes From: Peter Zijlstra To: Eric Dumazet Cc: Ingo Molnar , David Miller , "Rafael J. Wysocki" , linux-kernel@vger.kernel.org, kernel-testers@vger.kernel.org, Mike Galbraith , Linux Netdev List , Christoph Lameter , Christoph Hellwig , travis In-Reply-To: <1227778377.4454.1299.camel@twins> References: <20081121083044.GL16242@elte.hu> <49267694.1030506@cosmosbay.com> <20081121.010508.40225532.davem@davemloft.net> <4926AEDB.10007@cosmosbay.com> <4926D022.5060008@cosmosbay.com> <20081121152148.GA20388@elte.hu> <4926D39D.9050603@cosmosbay.com> <20081121153453.GA23713@elte.hu> <492DDC91.3020503@cosmosbay.com> <1227778377.4454.1299.camel@twins> Content-Type: text/plain Content-Transfer-Encoding: 7bit Date: Thu, 27 Nov 2008 10:39:31 +0100 Message-Id: <1227778771.4454.1311.camel@twins> Mime-Version: 1.0 X-Mailer: Evolution 2.24.1 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1656 Lines: 48 On Thu, 2008-11-27 at 10:33 +0100, Peter Zijlstra wrote: > On Thu, 2008-11-27 at 00:32 +0100, Eric Dumazet wrote: > > Avoids cache line ping pongs between cpus and prepare next patch, > > because updates of nr_inodes metric dont need inode_lock anymore. > > > > (socket8 bench result : 25s to 20.5s) > > > > Signed-off-by: Eric Dumazet > > --- > > > @@ -96,9 +96,40 @@ static DEFINE_MUTEX(iprune_mutex); > > * Statistics gathering.. > > */ > > struct inodes_stat_t inodes_stat; > > +static DEFINE_PER_CPU(int, nr_inodes); > > > > static struct kmem_cache * inode_cachep __read_mostly; > > > > +int get_nr_inodes(void) > > +{ > > + int cpu; > > + int counter = 0; > > + > > + for_each_possible_cpu(cpu) > > + counter += per_cpu(nr_inodes, cpu); > > + if (counter < 0) > > + counter = 0; > > + return counter; > > +} > > It would be good to get a cpu hotplug handler here and move to > for_each_online_cpu(). People are wanting distro's to be build with > NR_CPUS=4096. Also, this trade-off between global vs per_cpu only works if get_nr_inodes() is called significantly less than nr_inodes is changed. With it being called from writeback that might not be true for all workloads. One thing you can do about it is use the regular per-cpu counter stuff, which allows you to do an approximation of the global number (it also does all the hotplug stuff for you already). -- 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/