From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1760801Ab2DKRXf (ORCPT ); Wed, 11 Apr 2012 13:23:35 -0400 Received: from sabe.cs.wisc.edu ([128.105.6.20]:45004 "EHLO sabe.cs.wisc.edu" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1760711Ab2DKRXc (ORCPT ); Wed, 11 Apr 2012 13:23:32 -0400 Message-ID: <4F85BD2F.80905@cs.wisc.edu> Date: Wed, 11 Apr 2012 12:19:43 -0500 From: Mike Christie User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:11.0) Gecko/20120329 Thunderbird/11.0.1 MIME-Version: 1.0 To: Michael Tokarev CC: Jan Kara , Dave Chinner , Kernel Mailing List , SCSI Mailing List Subject: Re: dramatic I/O slowdown after upgrading 2.6.38->3.0+ References: <4F75E46E.2000503@msgid.tls.msk.ru> <20120405232913.GA6640@quack.suse.cz> <4F7E74F4.90604@msgid.tls.msk.ru> <20120410022628.GN18323@dastard> <4F83CC86.2010805@msgid.tls.msk.ru> <20120410151326.GA4936@quack.suse.cz> <4F855173.40902@msgid.tls.msk.ru> In-Reply-To: <4F855173.40902@msgid.tls.msk.ru> Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 04/11/2012 04:40 AM, Michael Tokarev wrote: > On 10.04.2012 19:13, Jan Kara wrote: >> > On Tue 10-04-12 10:00:38, Michael Tokarev wrote: > [] >>> >> 2.6.38: >>> >> # dd if=/dev/sdb of=/dev/null bs=1M iflag=direct count=100 >>> >> 100+0 records in >>> >> 100+0 records out >>> >> 104857600 bytes (105 MB) copied, 1.73126 s, 60.6 MB/s >>> >> >>> >> 3.0: >>> >> # dd if=/dev/sdb of=/dev/null bs=1M iflag=direct count=100 >>> >> 100+0 records in >>> >> 100+0 records out >>> >> 104857600 bytes (105 MB) copied, 29.4508 s, 3.6 MB/s >>> >> >>> >> That's about 20 times difference on direct read from the >>> >> same - idle - device!! >> > Huh, that's a huge difference for such a trivial load. So we can rule out >> > filesystems, writeback, mm. I also wouldn't think it's IO scheduler but >> > you can always check by comparing dd numbers after >> > echo none >/sys/block/sdb/queue/scheduler Did you try newer 3.X kernels or just 3.0? We were hitting a similar problem with iscsi. Same workload and it started with 2.6.38. I think it turned out to be this issue: // thread with issue like what we hit: http://thread.gmane.org/gmane.linux.kernel/1244680 // Patch that I think fixed issue: commit 3deaa7190a8da38453c4fabd9dec7f66d17fff67 Author: Shaohua Li Date: Fri Feb 3 15:37:17 2012 -0800 readahead: fix pipeline break caused by block plug