From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from cuda.sgi.com (cuda3.sgi.com [192.48.176.15]) by oss.sgi.com (8.12.11.20060308/8.12.11/SuSE Linux 0.7) with ESMTP id mBB0Kfqf005229 for ; Wed, 10 Dec 2008 18:20:41 -0600 Received: from partygirl.tmr.com (localhost [127.0.0.1]) by cuda.sgi.com (Spam Firewall) with ESMTP id 50664170E203 for ; Wed, 10 Dec 2008 16:20:39 -0800 (PST) Received: from partygirl.tmr.com (mail.tmr.com [64.65.253.246]) by cuda.sgi.com with ESMTP id 96bKd2JRC89BOjGj for ; Wed, 10 Dec 2008 16:20:39 -0800 (PST) Message-ID: <49405CD5.4070704@tmr.com> Date: Wed, 10 Dec 2008 19:20:37 -0500 From: Bill Davidsen MIME-Version: 1.0 Subject: Re: 12x performance drop on md/linux+sw raid1 due to barriers [xfs] References: In-Reply-To: List-Id: XFS Filesystem from SGI List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: xfs-bounces@oss.sgi.com Errors-To: xfs-bounces@oss.sgi.com To: Justin Piszcz Cc: linux-raid@vger.kernel.org, Alan Piszcz , xfs@oss.sgi.com Justin Piszcz wrote: > Someone should write a document with XFS and barrier support, if I > recall, > in the past, they never worked right on raid1 or raid5 devices, but it > appears now they they work on RAID1, which slows down performance ~12 > times!! > I would expect you, as an experienced tester, to have done this measurement more rigorously! I don't think it means much if this is what you did. > l1:~# /usr/bin/time tar xf linux-2.6.27.7.tar 0.15user 1.54system > 0:13.18elapsed 12%CPU (0avgtext+0avgdata 0maxresident)k > 0inputs+0outputs (0major+325minor)pagefaults 0swaps > l1:~# > > l1:~# /usr/bin/time tar xf linux-2.6.27.7.tar > 0.14user 1.66system 2:39.68elapsed 1%CPU (0avgtext+0avgdata > 0maxresident)k > 0inputs+0outputs (0major+324minor)pagefaults 0swaps > l1:~# > Before doing any disk test you need to start by dropping cache, to be sure the appropriate reproducible things happen. And in doing a timing test, you need to end with a sync for the same reason. So: echo 1 >/proc/sys/vm/drop_caches time bash -c "YOUR TEST; sync" This will give you a fair shot at being able to reproduce the results, done on an otherwise unloaded system. -- Bill Davidsen "Woe unto the statesman who makes war without a reason that will still be valid when the war is over..." Otto von Bismark _______________________________________________ xfs mailing list xfs@oss.sgi.com http://oss.sgi.com/mailman/listinfo/xfs