From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S262153AbULaU1J (ORCPT ); Fri, 31 Dec 2004 15:27:09 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S262154AbULaU1J (ORCPT ); Fri, 31 Dec 2004 15:27:09 -0500 Received: from sccrmhc12.comcast.net ([204.127.202.56]:50147 "EHLO sccrmhc12.comcast.net") by vger.kernel.org with ESMTP id S262153AbULaU1C (ORCPT ); Fri, 31 Dec 2004 15:27:02 -0500 Subject: Re: Queues when accessing disks From: "M. Edward Borasky" Reply-To: znmeb@cesmail.net To: Felipe Erias Cc: linux-kernel@vger.kernel.org In-Reply-To: <169c13c404123019322a766f64@mail.gmail.com> References: <169c13c404123019322a766f64@mail.gmail.com> Content-Type: text/plain Date: Fri, 31 Dec 2004 12:26:44 -0800 Message-Id: <1104524814.5185.28.camel@DreamGate> Mime-Version: 1.0 X-Mailer: Evolution 2.0.2 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org On Fri, 2004-12-31 at 04:32 +0100, Felipe Erias wrote: > Hi, > > I'm trying to apply queuing theory to the study of the GNU/Linux kernel. > Right now, I'm focusing in the queue of processes that appears when they > try to access an I/O device (specifically, an IDE HD). When they want to > read data, it behaves as a usual queue: several clients (processes) that > require attention from a server (disk / driver / ...). The case when they want > to write data is a bit more tricky, because of the cache buffers used by the OS, > and maybe could be modelized by a network of queues. Both cases are > interesting for my work, but I'll take the reading one first, just > because it seems > a bit more simple 'a priori'. > > To modelize the queue, I need to get some information: > - what processes claim attention from the disk > - when they do it > - when they begin to be served > - when they finish being served > > To get all this information, maybe I could hack my kernel a bit to write > a line to a log on every access to the HD, or account the IRQs from > the IDE channels... I also have the feeling that this queuing problem could > dissappear o became more hidden if DMA were enabled. > > To be true, I'm a bit lost and that's why I ask for your help. > > Yours sincerely, > > Felipe Erias I have a similar goal -- building an operational queueing model of a running Linux system. At this point, though, I'm not really trying to do per-process work, just model the system overall, including processors, I/O and virtual memory. As I noted in a recent posting, I'm currently blocked by the incorrect statistics gathered by a 2.4 kernel in "/proc/partitions". You can compute the throughputs, but not the average wait and service times, or the utilizations, which depend on the service times. I'm rather strongly considering establishing a mailing list just devoted to this topic -- queuing models of Linux kernels based on statistics the kernel collects. If such a list already exists, please let me know -- I don't want to re-invent any wheels, but there *is* a wheel I do want to invent! Please e-mail me off-list if you know of such a list or would join in if I create it. Thanks, Ed Borasky http://www.borasky-research.net/ > - > To unsubscribe from this list: send the line "unsubscribe linux-kernel" in > the body of a message to majordomo@vger.kernel.org > More majordomo info at http://vger.kernel.org/majordomo-info.html > Please read the FAQ at http://www.tux.org/lkml/