From owner-freebsd-current@FreeBSD.ORG Fri Oct 14 17:41:18 2005 Return-Path: X-Original-To: freebsd-current@freebsd.org 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 B49E716A41F for ; Fri, 14 Oct 2005 17:41:18 +0000 (GMT) (envelope-from anderson@centtech.com) Received: from mh1.centtech.com (moat3.centtech.com [207.200.51.50]) by mx1.FreeBSD.org (Postfix) with ESMTP id 7BEA443D66 for ; Fri, 14 Oct 2005 17:41:15 +0000 (GMT) (envelope-from anderson@centtech.com) Received: from [10.177.171.220] (neutrino.centtech.com [10.177.171.220]) by mh1.centtech.com (8.13.1/8.13.1) with ESMTP id j9EHfAmt011343; Fri, 14 Oct 2005 12:41:11 -0500 (CDT) (envelope-from anderson@centtech.com) Message-ID: <434FEDA1.4060803@centtech.com> Date: Fri, 14 Oct 2005 12:40:49 -0500 From: Eric Anderson User-Agent: Mozilla/5.0 (X11; U; FreeBSD i386; en-US; rv:1.7.11) Gecko/20050914 X-Accept-Language: en-us, en MIME-Version: 1.0 To: Brian Candler References: <200510131412.23525.max@love2party.net> <20051013181026.GB27418@odin.ac.hmc.edu> <20051014091004.GC18513@uk.tiscali.com> <20051014.085816.104604949.imp@bsdimp.com> <434FDAB2.7040402@centtech.com> <20051014164628.GA20338@uk.tiscali.com> In-Reply-To: <20051014164628.GA20338@uk.tiscali.com> Content-Type: text/plain; charset=us-ascii; format=flowed Content-Transfer-Encoding: 7bit X-Virus-Scanned: ClamAV 0.82/1134/Fri Oct 14 03:07:44 2005 on mh1.centtech.com X-Virus-Status: Clean Cc: max@love2party.net, freebsd-current@freebsd.org, "M. Warner Losh" Subject: Re: ufsstat - testers / feedback wanted! 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: Fri, 14 Oct 2005 17:41:18 -0000 Brian Candler wrote: > On Fri, Oct 14, 2005 at 11:20:02AM -0500, Eric Anderson wrote: > >>For statistics gathering purposes though, should I worry about this, or >>go for 'fast and imperfect' instead of 'perfect and slow'? With >>filesystems, I think it's more important to leave performance high and >>get a notion of the statistics, rather than impact performance for >>perfect stats (that you may only look at occasionally anyhow). > > > Losing the odd count probably isn't a problem, but I think there's the > possibility of a badly wrong value if you're updating a 64-bit word in two > halves. For example, it might be possible to wrap around from > 00000000ffffffff to 0000000000000000 instead of 0000000100000000. I suppose one could argue that this problem is no worse than using 32bit integers, except it would be right more often than not. (right?) Eric -- ------------------------------------------------------------------------ Eric Anderson Sr. Systems Administrator Centaur Technology Anything that works is better than anything that doesn't. ------------------------------------------------------------------------