From owner-freebsd-stable@FreeBSD.ORG Sat Jan 31 18:27:07 2009 Return-Path: Delivered-To: freebsd-stable@freebsd.org Received: from mx1.freebsd.org (mx1.freebsd.org [IPv6:2001:4f8:fff6::34]) by hub.freebsd.org (Postfix) with ESMTP id EEE001065705 for ; Sat, 31 Jan 2009 18:27:07 +0000 (UTC) (envelope-from rwatson@FreeBSD.org) Received: from cyrus.watson.org (cyrus.watson.org [65.122.17.42]) by mx1.freebsd.org (Postfix) with ESMTP id C9E908FC0A for ; Sat, 31 Jan 2009 18:27:07 +0000 (UTC) (envelope-from rwatson@FreeBSD.org) Received: from fledge.watson.org (fledge.watson.org [65.122.17.41]) by cyrus.watson.org (Postfix) with ESMTPS id 6D21746B0D; Sat, 31 Jan 2009 13:27:07 -0500 (EST) Date: Sat, 31 Jan 2009 18:27:07 +0000 (GMT) From: Robert Watson X-X-Sender: robert@fledge.watson.org To: Borja Marcos In-Reply-To: Message-ID: References: User-Agent: Alpine 2.00 (BSF 1167 2008-08-23) MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII; format=flowed Cc: freebsd-stable@freebsd.org Subject: Re: Puzzling change in performance X-BeenThere: freebsd-stable@freebsd.org X-Mailman-Version: 2.1.5 Precedence: list List-Id: Production branch of FreeBSD source code List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Sat, 31 Jan 2009 18:27:08 -0000 On Fri, 30 Jan 2009, Borja Marcos wrote: > The attached graphs are from a server running FreeBSD 7.1-i386 (now) with > the typical Apache2+MySQL with forums, Joomla... > > I just cannot explain this. Disk I/O bandwidth was suffering a lot, and > after the update the disks are almost idle. > > Any ideas? I cannot imagine a change between versions to justify this. The > latest update to 7-STABLE had been done in August. > > Maybe it was just degradation due to not being rebooted since August? But > it's strange anyway, and I had restarted MySQL and Apache some times during > this period. There are basically three ways to go about exploring this, none particularly good: (1) Do a more formal before and after analysis of performance on the box, perhaps using tools like kernel profiling, hwpmc, dtrace, etc. (2) Do a binary search to narrow down the date of the change that improved things until it becomes clear which mattered. (3) Hope someone annecdotally remembers something that might or might not be it and assume they're right. Of these, I'd guess (2) is actually the most effective way to go about it, but is potentially time-consuming. As you point out, the most interesting question is whether, when you go back to 7.0, things suddenly get slower again, or not. Typically long uptimes don't lead to performance problems on FreeBSD (in my experience) so I think that's unlikely to be the source. There are a lot of improvements in 7.1 relating to performance, but none particularly stands out for me as having the effect you describe. If you're really curious, I would try to pin it down with a binary search. Robert N M Watson Computer Laboratory University of Cambridge