From owner-freebsd-performance@FreeBSD.ORG Mon May 2 20:45:10 2005 Return-Path: Delivered-To: freebsd-performance@freebsd.org Received: from mx1.FreeBSD.org (mx1.freebsd.org [216.136.204.125]) by hub.freebsd.org (Postfix) with ESMTP id 33F8D16A4D3 for ; Mon, 2 May 2005 20:45:10 +0000 (GMT) Received: from cyrus.watson.org (cyrus.watson.org [204.156.12.53]) by mx1.FreeBSD.org (Postfix) with ESMTP id BC76743D1D for ; Mon, 2 May 2005 20:45:09 +0000 (GMT) (envelope-from rwatson@FreeBSD.org) Received: from fledge.watson.org (fledge.watson.org [204.156.12.50]) by cyrus.watson.org (Postfix) with ESMTP id 3C7D446B45; Mon, 2 May 2005 16:45:09 -0400 (EDT) Date: Mon, 2 May 2005 21:48:19 +0100 (BST) From: Robert Watson X-X-Sender: robert@fledge.watson.org To: Poul-Henning Kamp In-Reply-To: <19879.1115061648@critter.freebsd.dk> Message-ID: <20050502214208.M87351@fledge.watson.org> References: <19879.1115061648@critter.freebsd.dk> MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII; format=flowed cc: Eric Anderson cc: freebsd-performance@freebsd.org cc: Steven Hartland Subject: Re: Very low disk performance on 5.x X-BeenThere: freebsd-performance@freebsd.org X-Mailman-Version: 2.1.1 Precedence: list List-Id: Performance/tuning List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Mon, 02 May 2005 20:45:10 -0000 On Mon, 2 May 2005, Poul-Henning Kamp wrote: >> I'm quite willing to test and optimise things but so far no one has >> had any concrete suggestions on that to try. > > First thing I heard about this was a few hours ago. (Admittedly, my > email has been in a sucky state last week, so that is probably my own > fault). This is because I resent a message on the -performance list to you and Scott Long, and Soren because I was concerned that the thread was identifying a reproduceable problem for several people, but no one had really bit in to try and diagnose it :-). It seems likely we're hurting at a couple of levels, and it would be good to identify what's appearing at what level. I think comparing dd results on the total disk device directly as a starting point is a good place to begin. I'm not sure if we've seen Linux and FreeBSD dmsg output yet, but if nothing else it would be good to confirm if the drivers on both systems negotiate the same level of throughput to each drive. The next thing that would be quite nice to measure is the rate of I/O transactions per second we can get to the disk using the disk device directly, with a minimal transaction size. I have a vague recollection that you have to be careful in Linux because their character device nodes for disk devices are buffered, and you really want unbuffered I/O. After transactions/sec, broad sweeps across well-understood areas of the disk would be a good thing to do, again using the device node directly. Isolating the impact of the file system will be important... Robert N M Watson