From mboxrd@z Thu Jan 1 00:00:00 1970 From: Jeremy Higdon Subject: Re: Question about Qlogic performance in 2.6 kernel Date: Wed, 13 Oct 2004 20:03:41 -0700 Sender: linux-scsi-owner@vger.kernel.org Message-ID: <20041014030340.GA290349@sgi.com> References: <1097713700.3213.159.camel@hpti9.fsl.noaa.gov> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Return-path: Received: from omx2-ext.sgi.com ([192.48.171.19]:37330 "EHLO omx2.sgi.com") by vger.kernel.org with ESMTP id S269812AbUJNDDr (ORCPT ); Wed, 13 Oct 2004 23:03:47 -0400 Content-Disposition: inline In-Reply-To: <1097713700.3213.159.camel@hpti9.fsl.noaa.gov> List-Id: linux-scsi@vger.kernel.org To: Craig Tierney Cc: linux-scsi@vger.kernel.org On Wed, Oct 13, 2004 at 06:28:20PM -0600, Craig Tierney wrote: > I am seeing a large disparity in reads and writes from > my Raid box under the 2.6 kernel. I have tried this from > an Itanium box runing RHEL 4 beta and an Opteron box running > SUSE 9.1 professional. In both cases I am using 2 qlogic > QLA2200F HBAs. Each HBA talks to one lun from the array, and > I use dm to create a filesystem. > > Using lmdd to create a single stream of IO, I see 190 MB/s for > writes, but only 55 MB/s for reads. The vendor says reads and > writes can be as much as 300 MB/s if I had the right HBAs, but > the write performance is good for 2 1 Gb/s HBAs. > > I tried this with a 2.4 kernel on a dual Xeon box. Performance > was 150 MB/s for both reads and writes. The read performance was > that high only after I changed /proc/sys/vm/max-readahead to 1023. > > I tried changing the readahead size in 2.6 using blockdev. The > readahead was much larger by default than the 2.4 kernel. However, > no matter how large I set the readahead (as large as 1 MB), the > read performance did not change. > > I read on the kernel list that in the linux-2.6.9-rc3, some changes > to the readahead code path had been merged that was supposed to > simplify the logic. I tried the patch to see if affected performance. > It did not. > > Does anyone have some suggestions on how to improve the read performance > under 2.6? > > Thanks, > Craig It's my experience that changing readahead on devices under a dm volume does not actually change the amount of readahead you get. Your results suggest that you may be having the same problem. jeremy