From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1762224AbXGEUWd (ORCPT ); Thu, 5 Jul 2007 16:22:33 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1760218AbXGEUWW (ORCPT ); Thu, 5 Jul 2007 16:22:22 -0400 Received: from nz-out-0506.google.com ([64.233.162.237]:36160 "EHLO nz-out-0506.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1760102AbXGEUWV (ORCPT ); Thu, 5 Jul 2007 16:22:21 -0400 DomainKey-Signature: a=rsa-sha1; c=nofws; d=gmail.com; s=beta; h=received:message-id:date:from:to:subject:cc:in-reply-to:mime-version:content-type:content-transfer-encoding:content-disposition:references; b=GwSUlXKZbeWIYRfY5jkgE6Aq14K5cGenWW2hzeWgz+3PO6oNGzD+vmKwyvMNNO1iep2MQY/YBKI9YqsoPwrb3MrwNxyKKJ/Zyqmtg6Kl8zZdyzis6vgeenuF80oXPnw5kSI5rAWZFMsqrxHPTB3MD0eoAse4x2zB/TVVdlfCyxk= Message-ID: <9a8748490707051322r6e57a8b2xc381ef3c423d3403@mail.gmail.com> Date: Thu, 5 Jul 2007 22:22:19 +0200 From: "Jesper Juhl" To: knobi@knobisoft.de Subject: Re: Understanding I/O behaviour Cc: linux-kernel@vger.kernel.org In-Reply-To: <867098.12378.qm@web32607.mail.mud.yahoo.com> MIME-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Content-Disposition: inline References: <867098.12378.qm@web32607.mail.mud.yahoo.com> Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org On 05/07/07, Martin Knoblauch wrote: > Hi, > > for a customer we are operating a rackful of HP/DL380/G4 boxes that > have given us some problems with system responsiveness under [I/O > triggered] system load. > > The systems in question have the following HW: > > 2x Intel/EM64T CPUs > 8GB memory > CCISS Raid controller with 4x72GB SCSI disks as RAID5 > 2x BCM5704 NIC (using tg3) > > The distribution is RHEL4. We have tested several kernels including > the original 2.6.9, 2.6.19.2, 2.6.22-rc7 and 2.6.22-rc7+cfs-v18. > > One part of the workload is when several processes try to write 5 GB > each to the local filesystem (ext2->LVM->CCISS). When this happens, the > load goes up to 12 and responsiveness goes down. This means from one > moment to the next things like opening a ssh connection to the host in > question, or doing "df" take forever (minutes). Especially bad with the > vendor kernel, better (but not perfect) with 2.6.19 and 2.6.22-rc7. > > The load basically comes from the writing processes and up to 12 > "pdflush" threads all being in "D" state. > > So, what I would like to understand is how we can maximize the > responsiveness of the system, while keeping disk throughput at maximum. > I'd suspect you can't get both at 100%. I'd guess you are probably using a 100Hz no-preempt kernel. Have you tried a 1000Hz + preempt kernel? Sure, you'll get a bit lower overall throughput, but interactive responsiveness should be better - if it is, then you could experiment with various combinations of CONFIG_PREEMPT, CONFIG_PREEMPT_VOLUNTARY, CONFIG_PREEMPT_NONE and CONFIG_HZ_1000, CONFIG_HZ_300, CONFIG_HZ_250, CONFIG_HZ_100 to see what gives you the best balance between throughput and interactive responsiveness (you could also throw CONFIG_PREEMPT_BKL and/or CONFIG_NO_HZ, but I don't think the impact will be as significant as with the other options, so to keep things simple I'd leave those out at first) . I'd guess that something like CONFIG_PREEMPT_VOLUNTARY + CONFIG_HZ_300 would probably be a good compromise for you, but just to see if there's any effect at all, start out with CONFIG_PREEMPT + CONFIG_HZ_1000. Hope that helps. (PS. please don't do crap like using that spamtrap@ address and have people manually replace it with the one from your .signature when posting on LKML - it's annoying as hell) -- Jesper Juhl Don't top-post http://www.catb.org/~esr/jargon/html/T/top-post.html Plain text mails only, please http://www.expita.com/nomime.html