From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S964819AbWFHOAS (ORCPT ); Thu, 8 Jun 2006 10:00:18 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S964843AbWFHOAR (ORCPT ); Thu, 8 Jun 2006 10:00:17 -0400 Received: from ns.virtualhost.dk ([195.184.98.160]:55831 "EHLO virtualhost.dk") by vger.kernel.org with ESMTP id S964819AbWFHOAQ (ORCPT ); Thu, 8 Jun 2006 10:00:16 -0400 Date: Thu, 8 Jun 2006 16:00:13 +0200 From: Jens Axboe To: Andi Kleen Cc: Voluspa , akpm@osdl.org, Valdis.Kletnieks@vt.edu, diegocg@gmail.com, linux-kernel@vger.kernel.org, wfg@mail.ustc.edu.cn Subject: Re: adaptive readahead overheads Message-ID: <20060608140012.GD5207@suse.de> References: <349406446.10828@ustc.edu.cn> <20060604020738.31f43cb0.akpm@osdl.org> <1149413103.3109.90.camel@laptopd505.fenrus.org> <20060605031720.0017ae5e.lista1@comhem.se> <349562623.17723@ustc.edu.cn> <20060608094356.5c1272cc.lista1@comhem.se> <349766648.27054@ustc.edu.cn> <20060608142556.2e10e379.lista1@comhem.se> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org On Thu, Jun 08 2006, Andi Kleen wrote: > Voluspa writes: > > > On Thu, 8 Jun 2006 19:37:31 +0800 Fengguang Wu wrote: > > > I'd like to show some numbers on the pure software overheads come with > > > the adaptive readahead in daily operations. > > [...] > > > > > > # time find /usr -type f -exec md5sum {} \; >/dev/null > > > > > > ARA > > > > > > 406.00s user 325.16s system 97% cpu 12:28.17 total > > > > Just out of interest, all your figures show an almost maxed out CPU. > > It might be because qemu has a poor IO model (old IDE) that is quite > CPU intensive to drive. qemu ide supports dma, so it's ok in that respect. It doesn't support async io for the host though, so all io ends up blocking waiting for io to complete at the host. I would not advocate using qemu for benching these things, it's just not (yet) well suited for io testing. -- Jens Axboe