From mboxrd@z Thu Jan 1 00:00:00 1970 From: Dominik Brodowski Subject: direct-io regression [Was: How to track down abysmal performance ata - raid1 - crypto - vg/lv - xfs] Date: Thu, 5 Aug 2010 11:31:00 +0200 Message-ID: <20100805093100.GA3001@comet.dominikbrodowski.net> References: <20100804073546.GA7494@comet.dominikbrodowski.net> <20100804085039.GA11671@infradead.org> <20100804091317.GA27779@isilmar-3.linta.de> <20100804092122.GA2998@infradead.org> <20100804073546.GA7494@comet.dominikbrodowski.net> <201008041116.09822@zmi.at> <20100804102526.GB13766@isilmar-3.linta.de> <15446.1280953986@localhost> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Return-path: Content-Disposition: inline In-Reply-To: <15446.1280953986@localhost> Sender: linux-kernel-owner@vger.kernel.org To: Valdis.Kletnieks@vt.edu, josef@redhat.com, chris.mason@oracle.com Cc: Michael Monnerie , Christoph Hellwig , linux-raid@vger.kernel.org, xfs@oss.sgi.com, linux-kernel@vger.kernel.org, dm-devel@redhat.com List-Id: dm-devel.ids Hey, when attempting to track down insufficient I/O performance, I found the following reression relating to direct-io on my notebook, where an ata device, which consists of several partitions, is combined to a lvm volume, and one logical volume is then encrypted using dm-crypt. Test case was the following command: $ dd if=/dev/mapper/vg0-root_crypt of=/dev/zero iflag=direct bs=8k count=131072 2.6.34 results in ~16 MB/s, 2.6.35 results in ~ 3.1 MB/s The regression was bisected down to the follwoing commit: commit c2c6ca417e2db7a519e6e92c82f4a933d940d076 Author: Josef Bacik Date: Sun May 23 11:00:55 2010 -0400 direct-io: do not merge logically non-contiguous requests ... How to fix this? I do not use btrfs, but ext3 (and the access was down on the block level, not on the fs level, so this btrs-related commit should not cause such a regression). Best, Dominik