From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Message-ID: <507548FE.9010106@cran.org.uk> Date: Wed, 10 Oct 2012 11:07:58 +0100 From: Bruce Cran MIME-Version: 1.0 Subject: Re: FIO 2.0.9 for Windows Server 2008 RC1 SP2 reports extreme latencies References: <50605FEF.5020103@cran.org.uk> <50632E0D.4090003@cran.org.uk> <506693F8.3010903@kernel.dk> <5066FBC0.5040508@cran.org.uk> In-Reply-To: Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit To: "Jeffrey McVay (jmcvay)" Cc: Jens Axboe , "fio@vger.kernel.org" List-ID: On 06/10/2012 01:25, Jeffrey McVay (jmcvay) wrote: > Anything new on this issue? There is a reviewer using FIO on Windows to measure latency values. I am concerned that they may publish inaccurate data. I'm working on it again today. The problem is that windowsaio iterates over the list of outstanding IOs (busylist), but that list has the most recent first. The sequence of queue/dequeue with an iodepth of 4 is: queue 1 queue 2 queue 3 queue 4 dequeue 4 queue 5 dequeue 5 queue 6 dequeue 6 dequeue 3 dequeue 2 dequeue 1 So the first IO therefore has an apparent latency equal to the runtime of fio. -- Bruce Cran