From mboxrd@z Thu Jan 1 00:00:00 1970 From: Craig Tierney Subject: Re: Question about Qlogic performance in 2.6 kernel Date: Thu, 14 Oct 2004 06:41:08 -0600 Sender: linux-scsi-owner@vger.kernel.org Message-ID: <1097757667.2939.9.camel@localhost.localdomain> References: <1097713700.3213.159.camel@hpti9.fsl.noaa.gov> <20041014030340.GA290349@sgi.com> Mime-Version: 1.0 Content-Type: text/plain Content-Transfer-Encoding: 7bit Return-path: Received: from system65-210-78-197.hpti.com ([65.210.78.197]:2913 "EHLO hptimail01.HPTI.COM") by vger.kernel.org with ESMTP id S263778AbUJNMn6 (ORCPT ); Thu, 14 Oct 2004 08:43:58 -0400 In-Reply-To: <20041014030340.GA290349@sgi.com> List-Id: linux-scsi@vger.kernel.org To: Jeremy Higdon Cc: linux-scsi@vger.kernel.org On Wed, 2004-10-13 at 21:03, Jeremy Higdon wrote: > 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. I read that somewhere in the docs at one point. I tried changing the readahead on the dm and on the luns themselves. By running blockdev, I saw that the values did indeed change for the luns. My read tests showed no change in performance when I read from the filesystem or each of the luns directly. Craig