From owner-freebsd-current@FreeBSD.ORG Wed Jul 28 09:44:47 2004 Return-Path: Delivered-To: freebsd-current@freebsd.org Received: from mx1.FreeBSD.org (mx1.freebsd.org [216.136.204.125]) by hub.freebsd.org (Postfix) with ESMTP id A1DA116A4CE; Wed, 28 Jul 2004 09:44:47 +0000 (GMT) Received: from mail.dt.e-technik.uni-dortmund.de (krusty.dt.e-technik.Uni-Dortmund.DE [129.217.163.1]) by mx1.FreeBSD.org (Postfix) with ESMTP id 0AA7343D1F; Wed, 28 Jul 2004 09:44:47 +0000 (GMT) (envelope-from ma@dt.e-technik.uni-dortmund.de) Received: from m2a2.dyndns.org (p5487C099.dip.t-dialin.net [84.135.192.153]) CF14F36A90; Wed, 28 Jul 2004 11:44:45 +0200 (CEST) Received: from localhost (localhost [127.0.0.1]) by merlin.emma.line.org (Postfix) with ESMTP id 1AA0BBD3FC; Wed, 28 Jul 2004 11:44:44 +0200 (CEST) Received: from merlin.emma.line.org ([127.0.0.1]) by localhost (m2a2.dyndns.org [127.0.0.1]) (amavisd-new, port 10024) with LMTP id 14877-02-2; Wed, 28 Jul 2004 11:44:44 +0200 (CEST) Received: by merlin.emma.line.org (Postfix, from userid 500) id E6D6CBD3F9; Wed, 28 Jul 2004 11:44:43 +0200 (CEST) To: Garrett Wollman In-Reply-To: <200407262220.i6QMKMT0098911@khavrinen.lcs.mit.edu> (Garrett Wollman's message of "Mon, 26 Jul 2004 18:20:22 -0400 (EDT)") References: <1090718450.2020.4.camel@illusion.com> <200407251112.46183.doconnor@gsoft.com.au> <20040726175219.GA96815@green.homeunix.org> <20040726155712.R32601@pooker.samsco.org> <200407262220.i6QMKMT0098911@khavrinen.lcs.mit.edu> From: Matthias Andree Date: Wed, 28 Jul 2004 11:44:43 +0200 Message-ID: User-Agent: Gnus/5.110003 (No Gnus v0.3) Emacs/21.3 (gnu/linux) MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii X-Virus-Scanned: by amavisd-new at m2a2.dyndns.org cc: Scott Long cc: current@FreeBSD.ORG Subject: Re: magic sysrq keys functionality X-BeenThere: freebsd-current@freebsd.org X-Mailman-Version: 2.1.1 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: Wed, 28 Jul 2004 09:44:47 -0000 Garrett Wollman writes: > < said: > >> This works right now because we assume that disks will commit blocks >> in order, and that assumption generally hasn't been broken. > > I don't think soft updates cares about what order blocks are > committed, because it will not in general consider a dependency > resolved until it is notified that the buffer has been written. What > we do assume is that the disk (or driver) doesn't lie to us and claim > that a block was written when it really wasn't. Makes me wonder about efficiency (write latency). I admit I'm not familiar with how the buffers are scheduled in particular, if there are "write batches" or something. If however softdep needs to wait for individual blocks, real tagged queueing (with ordered tags in the right places and such) might be faster because the drive can then decide for itself in which order the blocks are written to the disks fastest, without violating any of the ordering assumptions softupdates code relies on. -- Matthias Andree Encrypted mail welcome: my GnuPG key ID is 0x052E7D95 (PGP/MIME preferred)