From mboxrd@z Thu Jan 1 00:00:00 1970 From: Bill Davidsen Subject: Re: 12x performance drop on md/linux+sw raid1 due to barriers [xfs] Date: Wed, 10 Dec 2008 19:20:37 -0500 Message-ID: <49405CD5.4070704@tmr.com> References: Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: Sender: linux-raid-owner@vger.kernel.org To: Justin Piszcz Cc: linux-raid@vger.kernel.org, xfs@oss.sgi.com, Alan Piszcz List-Id: linux-raid.ids 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