From: Kay Diederichs Subject: ext4 performance regression 2.6.27-stable versus 2.6.32 and later Date: Wed, 28 Jul 2010 21:51:48 +0200 Message-ID: <4C508A54.7070002@uni-konstanz.de> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: QUOTED-PRINTABLE Cc: Ext4 Developers List , Karsten Schaefer To: linux Return-path: Received: from pyrimidin.rz.uni-konstanz.de ([134.34.240.46]:57163 "EHLO pyrimidin.rz.uni-konstanz.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751655Ab0G1UBr (ORCPT ); Wed, 28 Jul 2010 16:01:47 -0400 Sender: linux-ext4-owner@vger.kernel.org List-ID: Dear all, we reproducibly find significantly worse ext4 performance when our fileservers run 2.6.32 or later kernels, when compared to the 2.6.27-stable series. The hardware is RAID5 of 5 1TB WD10EACS disks (giving almost 4TB) in an external eSATA enclosure (STARDOM ST6600); disks are not partitioned bu= t rather the complete disks are used: md5 : active raid5 sde[0] sdg[5] sdd[3] sdc[2] sdf[1] 3907045376 blocks super 1.2 level 5, 512k chunk, algorithm 2 [5/5] [UUUUU] The enclosure is connected using a Silicon Image (supported by sata_sil24) PCIe-X1 adapter to one of our fileservers (either the backu= p fileserver, 32bit desktop hardware with Intel(R) Pentium(R) D CPU 3.40GHz, or a production-fileserver 64bit Precision WorkStation 670 w/ = 2 Xeon 3.2GHz). The ext4 filesystem was created using mke2fs -j -T largefile -E stride=3D128,stripe_width=3D512 -O extent,uni= nit_bg It is mounted with noatime,data=3Dwriteback As operating system we usually use RHEL5.5, but to exclude problems wit= h self-compiled kernels, we also booted USB sticks with latest Fedora12 and FC13 . Our benchmarks consist of copying 100 6MB files from and to the RAID5, over NFS (NVSv3, GB ethernet, TCP, async export), and tar-ing and rsync-ing kernel trees back and forth. Before and after each individual benchmark part, we "sync" and "echo 3 > /proc/sys/vm/drop_caches" on both the client and the server. The problem: with 2.6.27.48 we typically get: 44 seconds for preparations 23 seconds to rsync 100 frames with 597M from nfs directory 33 seconds to rsync 100 frames with 595M to nfs directory 50 seconds to untar 24353 kernel files with 323M to nfs directory 56 seconds to rsync 24353 kernel files with 323M from nfs directory 67 seconds to run xds_par in nfs directory (reads and writes 600M) 301 seconds to run the script with 2.6.32.16 we find: 49 seconds for preparations 23 seconds to rsync 100 frames with 597M from nfs directory 261 seconds to rsync 100 frames with 595M to nfs directory 74 seconds to untar 24353 kernel files with 323M to nfs directory 67 seconds to rsync 24353 kernel files with 323M from nfs directory 290 seconds to run xds_par in nfs directory (reads and writes 600M) 797 seconds to run the script This is quite reproducible (times varying about 1-2% or so). All times include reading and writing on the client side (stock CentOS5.5 Nehalem machines with fast single SATA disks). The 2.6.32.16 times are the same with FC12 and FC13 (booted from USB stick). The 2.6.27-versus-2.6.32+ regression cannot be due to barriers because md RAID5 does not support barriers ("JBD: barrier-based sync failed on md5 - disabling barriers"). What we tried: noop and deadline schedulers instead of cfq; modifications of /sys/block/sd[c-g]/queue/max_sectors_kb; switching on/off NCQ; blockdev --setra 8192 /dev/md5; increasing /sys/block/md5/md/stripe_cache_size When looking at the I/O statistics while the benchmark is running, we see very choppy patterns for 2.6.32, but quite smooth stats for 2.6.27-stable. It is not an NFS problem; we see the same effect when transferring the data using an rsync daemon. We believe, but are not sure, that the problem does not exist with ext3 - it's not so quick to re-format a 4 T= B volume. Any ideas? We cannot believe that a general ext4 regression should have gone unnoticed. So is it due to the interaction of ext4 with md-RAID5 ? thanks, Kay --=20 Kay Diederichs http://strucbio.biologie.uni-konstanz.de email: Kay.Diederichs@uni-konstanz.de Tel +49 7531 88 4049 Fax 3183 =46achbereich Biologie, Universit=E4t Konstanz, Box M647, D-78457 Konst= anz. -- To unsubscribe from this list: send the line "unsubscribe linux-ext4" i= n the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html