From owner-freebsd-current@FreeBSD.ORG Mon Jan 9 00:22:12 2012 Return-Path: Delivered-To: current@freebsd.org Received: from mx1.freebsd.org (mx1.freebsd.org [IPv6:2001:4f8:fff6::34]) by hub.freebsd.org (Postfix) with ESMTP id 428A6106567C; Mon, 9 Jan 2012 00:22:12 +0000 (UTC) (envelope-from kostikbel@gmail.com) Received: from mail.zoral.com.ua (mx0.zoral.com.ua [91.193.166.200]) by mx1.freebsd.org (Postfix) with ESMTP id CF1668FC25; Mon, 9 Jan 2012 00:22:11 +0000 (UTC) Received: from skuns.kiev.zoral.com.ua (localhost [127.0.0.1]) by mail.zoral.com.ua (8.14.2/8.14.2) with ESMTP id q090M8wV015151 (version=TLSv1/SSLv3 cipher=DHE-RSA-AES256-SHA bits=256 verify=NO); Mon, 9 Jan 2012 02:22:08 +0200 (EET) (envelope-from kostikbel@gmail.com) Received: from deviant.kiev.zoral.com.ua (kostik@localhost [127.0.0.1]) by deviant.kiev.zoral.com.ua (8.14.5/8.14.5) with ESMTP id q090M78U048771; Mon, 9 Jan 2012 02:22:07 +0200 (EET) (envelope-from kostikbel@gmail.com) Received: (from kostik@localhost) by deviant.kiev.zoral.com.ua (8.14.5/8.14.5/Submit) id q090M7Kh048770; Mon, 9 Jan 2012 02:22:07 +0200 (EET) (envelope-from kostikbel@gmail.com) X-Authentication-Warning: deviant.kiev.zoral.com.ua: kostik set sender to kostikbel@gmail.com using -f Date: Mon, 9 Jan 2012 02:22:07 +0200 From: Kostik Belousov To: Don Lewis Message-ID: <20120109002207.GS31224@deviant.kiev.zoral.com.ua> References: <8334.1326061310@critter.freebsd.dk> <201201090009.q09090sR024751@gw.catspoiler.org> Mime-Version: 1.0 Content-Type: multipart/signed; micalg=pgp-sha1; protocol="application/pgp-signature"; boundary="USvVzkgzuRvOAB6v" Content-Disposition: inline In-Reply-To: <201201090009.q09090sR024751@gw.catspoiler.org> User-Agent: Mutt/1.4.2.3i X-Virus-Scanned: clamav-milter 0.95.2 at skuns.kiev.zoral.com.ua X-Virus-Status: Clean X-Spam-Status: No, score=-3.9 required=5.0 tests=ALL_TRUSTED,AWL,BAYES_00 autolearn=ham version=3.2.5 X-Spam-Checker-Version: SpamAssassin 3.2.5 (2008-06-10) on skuns.kiev.zoral.com.ua Cc: phk@phk.freebsd.dk, current@freebsd.org Subject: Re: CD9660/md(4)/UFS22 silly behaviour X-BeenThere: freebsd-current@freebsd.org X-Mailman-Version: 2.1.5 Precedence: list List-Id: Discussions about the use of FreeBSD-current List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Mon, 09 Jan 2012 00:22:12 -0000 --USvVzkgzuRvOAB6v Content-Type: text/plain; charset=us-ascii Content-Disposition: inline Content-Transfer-Encoding: quoted-printable On Sun, Jan 08, 2012 at 04:09:00PM -0800, Don Lewis wrote: > On 8 Jan, Poul-Henning Kamp wrote: > >=20 > > I'm doing som data-mining on a pile of ISO images right now. > >=20 > > I stuck the ISOs on a UFS2 on a flash-disk for speed, and mdconfig(8)'d > > them so I could mount them. > >=20 > > The traffic pattern his "interesting": > >=20 > > dT: 1.003s w: 1.000s > > L(q) ops/s r/s kBps ms/r w/s kBps ms/w %busy Name > > [...] > > 1 733 733 1466 1.3 0 0 0.0 98.2| md39 > > 1 733 733 23449 1.3 0 0 0.0 93.2| da0 > >=20 > > Notice the 1:16 ratio on kBps but 1:1 ratio on ops/s ? > >=20 > > da0's UFS2 has 32k block-size: > >=20 > > magic 19540119 (UFS2) time Wed Jan 4 16:41:47 2012 > > superblock location 65536 id [ 4f046cf5 c30697ee ] > > ncg 104 size 19537685 blocks 19228156 > > bsize 32768 shift 15 mask 0xffff8000 > > fsize 4096 shift 12 mask 0xfffff000 > > [...] > >=20 > > It looks like every 2k read from CD9660 turns into a 32k block > > read in the UFS filesystem, without any beneficial caching happening. >=20 > Probably some confusion about which filesystem layer owns the cached > data. It would probably be inefficient to cache the data in both > places. The best fix would probably be for CD9660 to think that the > underlying device has 32Kb sectors. I discussed the issue with phk further. The reason for discarding the 30K of the read 32K block is that md(4) supplies IO_DIRECT flag for VOP_READ, and FFS avoids putting the read data into any cache. Most likely, we can implement a sysctl that would disable direct reads, at the cost of double-buffering the data. For obvious reasons, it is impossible to disable caching from the filesystem living on top of md(4) volume. --USvVzkgzuRvOAB6v Content-Type: application/pgp-signature Content-Disposition: inline -----BEGIN PGP SIGNATURE----- Version: GnuPG v1.4.11 (FreeBSD) iEYEARECAAYFAk8KMy8ACgkQC3+MBN1Mb4j5qgCdHaENMMnaDpnCXXfixPbhCMe0 dkYAoNJKskwI+VVj8zDiuQJEO7byzvQh =soav -----END PGP SIGNATURE----- --USvVzkgzuRvOAB6v--