Date: Wed, 21 Feb 2007 05:21:13 +1100 From: Peter Jeremy <peterjeremy@optushome.com.au> To: Zaphod Beeblebrox <zbeeble@gmail.com> Cc: freebsd-hackers@freebsd.org Subject: Re: Fwd: Abyssmal dump cache efficiency Message-ID: <20070220182113.GC853@turion.vk2pj.dyndns.org> In-Reply-To: <5f67a8c40702192347h7383a238v2ff212b38404eb70@mail.gmail.com> References: <20070218002758.GQ859@turion.vk2pj.dyndns.org> <5f67a8c40702192346re1ada13gcfb3d10db6139cde@mail.gmail.com> <5f67a8c40702192347h7383a238v2ff212b38404eb70@mail.gmail.com>
next in thread | previous in thread | raw e-mail | index | archive | help
--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 <zbeeble@gmail.com> wrote: >On 2/17/07, Peter Jeremy <peterjeremy@optushome.com.au> 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--
Want to link to this message? Use this URL: <https://mail-archive.FreeBSD.org/cgi/mid.cgi?20070220182113.GC853>