This message generated a parse failure. Raw output follows here. Please use 'back' to navigate. From devnull@lkml.org Wed Apr 24 03:47:17 2024 Received: from spaans.ds9a.nl (adsl-xs4all.ds9a.nl [213.84.159.51]) by kylie.puddingonline.com (8.11.6/8.11.6) with SMTP id g8IFkDX18525 for ; Wed, 18 Sep 2002 17:46:16 +0200 Received: (qmail 23013 invoked from network); 18 Sep 2002 07:05:19 -0000 Received: from unknown (HELO spaans.ds9a.nl) (3ffe:8280:10:360:202:44ff:fe2a:a1dd) by mayo.ipv6.ds9a.nl with SMTP; 18 Sep 2002 07:05:19 -0000 Received: (qmail 1042 invoked by uid 1000); 17 Sep 2002 20:44:05 -0000 Received: (maildatabase); juh Received: (qmail 1777 invoked by alias); 9 Nov 2001 06:39:56 -0000 Received: (qmail 1679 invoked from network); 9 Nov 2001 06:39:47 -0000 Received: from digger.ds9a.nl (HELO outpost.powerdns.com) (postfix@::ffff:213.244.168.211) by spaans.ds9a.nl with SMTP; 9 Nov 2001 06:39:47 -0000 Received: from vvtp.nl (vvtp.tn.tudelft.nl [130.161.252.29]) by outpost.powerdns.com (Postfix) with SMTP id A208FC64E1 for ; Fri, 9 Nov 2001 07:16:34 +0100 (CET) Received: (qmail 25832 invoked by uid 2547); 9 Nov 2001 06:16:29 -0000 Received: (qmail 25749 invoked from network); 9 Nov 2001 06:16:24 -0000 Received: from vger.kernel.org (199.183.24.194) by vvtp.tn.tudelft.nl with SMTP; 9 Nov 2001 06:16:24 -0000 Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id ; Fri, 9 Nov 2001 01:14:03 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id ; Fri, 9 Nov 2001 01:13:53 -0500 Received: from vasquez.zip.com.au ([203.12.97.41]:27656 "EHLO vasquez.zip.com.au") by vger.kernel.org with ESMTP id ; Fri, 9 Nov 2001 01:13:44 -0500 Received: from zip.com.au (root@zipperii.zip.com.au [61.8.0.87]) by vasquez.zip.com.au (8.9.3/8.9.3/Debian 8.9.3-21) with ESMTP id RAA07866; Fri, 9 Nov 2001 17:13:32 +1100 X-Authentication-Warning: vasquez.zip.com.au: Host root@zipperii.zip.com.au [61.8.0.87] claimed to be zip.com.au Message-Id: <3BEB72DA.7ADA8332@zip.com.au> Date: Thu, 08 Nov 2001 22:08:26 -0800 From: Andrew Morton X-Mailer: Mozilla 4.77 [en] (X11; U; Linux 2.4.14-pre8 i686) X-Accept-Language: en Mime-Version: 1.0 To: Jeremy Fitzhardinge Cc: Constantin Loizides , Linux Kernel List Subject: Re: [Ext2-devel] disk throughput References: <3BEAA3B7.A7F9328E@isg.de>, <3BE647F4.AD576FF2@zip.com.au> <3BE71131.59BA0CFC@zip.com.au> <20011106105138Z16653-12382+40@humbolt.nl.linux.org> <1005063444.25686.18.camel@ixodes.goop.org> Content-Type: text/plain; charset=us-ascii Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org X-AntiVirus: scanned for viruses by AMaViS 0.2.1 (http://amavis.org/) X-AntiVirus: scanned for viruses by AMaViS 0.2.1 (http://amavis.org/) X-Spam-Tag: 1 Lines: 51 Jeremy Fitzhardinge wrote: > > On Thu, 2001-11-08 at 07:24, Constantin Loizides wrote: > > > > > This is one I made a while ago while doing some measurements; its also > > <[snip] > > > > That's an interesting plot. I would like to do one for my disk! > > > > How did you do it? > > How do you find out about the seek distance??? > > Do you create one big file and then start > > seeking around accessing different blocks of it? > > Its pretty simple. I open /dev/hda (the whole device), and read random > blocks, timing how long it takes for the data to come back since the > last one. I set up a few hundred/thousand buckets, and accumulate the > measured time into the bucket for that seek distance. So: > > fd=open("/dev/hda") > llseek(fd, last = rand()); > read(fd) > while(!finished) { > blk = rand(); > llseek(fd, blk); > read(fd); > bucket[abs(last-blk)] = time; > last = blk; > } How do you avoid aftifacts from Linux caching with this test? > I found the random seeking was the only way I could get reasonable > numbers out of the drive; any of the ordered patterns of the form "OK, > lets measure N block seeks" seemed to be predicted by the drive and gave > unreasonably fast results. > But we *want* unreasonably fast results! We need to understand this device-level prediction, then decide if it's sufficiently widespread for us to go and exploit the hell out of it. Have you any ideas as to what's happening? - - 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/