From owner-freebsd-hackers@FreeBSD.ORG Tue Feb 20 18:21:15 2007 Return-Path: X-Original-To: freebsd-hackers@freebsd.org Delivered-To: freebsd-hackers@freebsd.org Received: from mx1.freebsd.org (mx1.freebsd.org [69.147.83.52]) by hub.freebsd.org (Postfix) with ESMTP id E14A116BEA9 for ; Tue, 20 Feb 2007 18:21:15 +0000 (UTC) (envelope-from peterjeremy@optushome.com.au) Received: from turion.vk2pj.dyndns.org (c220-239-3-125.belrs4.nsw.optusnet.com.au [220.239.3.125]) by mx1.freebsd.org (Postfix) with ESMTP id 54EE913C491 for ; Tue, 20 Feb 2007 18:21:15 +0000 (UTC) (envelope-from peterjeremy@optushome.com.au) Received: from turion.vk2pj.dyndns.org (localhost.vk2pj.dyndns.org [127.0.0.1]) by turion.vk2pj.dyndns.org (8.13.8/8.13.8) with ESMTP id l1KILDt9003522; Wed, 21 Feb 2007 05:21:13 +1100 (EST) (envelope-from peter@turion.vk2pj.dyndns.org) Received: (from peter@localhost) by turion.vk2pj.dyndns.org (8.13.8/8.13.8/Submit) id l1KILDws003521; Wed, 21 Feb 2007 05:21:13 +1100 (EST) (envelope-from peter) Date: Wed, 21 Feb 2007 05:21:13 +1100 From: Peter Jeremy To: Zaphod Beeblebrox Message-ID: <20070220182113.GC853@turion.vk2pj.dyndns.org> References: <20070218002758.GQ859@turion.vk2pj.dyndns.org> <5f67a8c40702192346re1ada13gcfb3d10db6139cde@mail.gmail.com> <5f67a8c40702192347h7383a238v2ff212b38404eb70@mail.gmail.com> MIME-Version: 1.0 Content-Type: multipart/signed; micalg=pgp-sha1; protocol="application/pgp-signature"; boundary="KsGdsel6WgEHnImy" Content-Disposition: inline In-Reply-To: <5f67a8c40702192347h7383a238v2ff212b38404eb70@mail.gmail.com> X-PGP-Key: http://members.optusnet.com.au/peterjeremy/pubkey.asc User-Agent: Mutt/1.5.13 (2006-08-11) Cc: freebsd-hackers@freebsd.org Subject: Re: Fwd: Abyssmal dump cache efficiency X-BeenThere: freebsd-hackers@freebsd.org X-Mailman-Version: 2.1.5 Precedence: list List-Id: Technical Discussions relating to FreeBSD List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Tue, 20 Feb 2007 18:21:16 -0000 --KsGdsel6WgEHnImy Content-Type: text/plain; charset=us-ascii Content-Disposition: inline Content-Transfer-Encoding: quoted-printable On 2007-Feb-20 02:47:00 -0500, Zaphod Beeblebrox wrote: >On 2/17/07, Peter Jeremy wrote: >>I've tried modelling a unified cache along the NetBSD line and there >>appears to be a massive improvement in cache performance. It's unclear >>how much of an improvement this will give in overall performance but >>not physically reading data from disk must be faster than reading it. > >This squares perfectly with my recent observation that while runing some >combination of "dump | restore" that the dump disks incur 2 to 3 times more >I/O (reading) than the restore disks. Now... for "performance" I was using >the cache function --- maybe the cache is actually a detriment. The limited testing I've done suggests that 32MB cache gives you a 10-20% improvement in dump speed. This would heavily dependent on the disk I/O performance - a slow CPU running PIO might be better off without caching. I've found that you do get a worthwhile improvement in dump|restore performance by introducing a large (10's of MB) fifo between them. This helps reduce synchronisation between dump and restore (so that dump can continue to read whilst restore is busy writing a batch of small files and vice versa). There's a suitable port but I can't recall the name because I wrote my own. >>I believe it would be worthwhile creating a todo item to investigate >>this more thoroughly. Note that I think that fixing this is a weekend job, rather than a SoC project. --=20 Peter Jeremy --KsGdsel6WgEHnImy Content-Type: application/pgp-signature Content-Disposition: inline -----BEGIN PGP SIGNATURE----- Version: GnuPG v1.4.6 (FreeBSD) iD8DBQFF2zwZ/opHv/APuIcRApXPAJoD+HdLzlfXkAm9lUZL4YKphYvaBQCeLG5p l+SG5zWqFEIRdbQUTMR1Vac= =i5Zh -----END PGP SIGNATURE----- --KsGdsel6WgEHnImy--