From owner-freebsd-current@FreeBSD.ORG Fri Apr 13 18:55:08 2007 Return-Path: X-Original-To: freebsd-current@freebsd.org Delivered-To: freebsd-current@freebsd.org Received: from mx1.freebsd.org (mx1.freebsd.org [69.147.83.52]) by hub.freebsd.org (Postfix) with ESMTP id A416616A400 for ; Fri, 13 Apr 2007 18:55:08 +0000 (UTC) (envelope-from uspoerlein@gmail.com) Received: from ug-out-1314.google.com (ug-out-1314.google.com [66.249.92.175]) by mx1.freebsd.org (Postfix) with ESMTP id 28BB013C45A for ; Fri, 13 Apr 2007 18:55:07 +0000 (UTC) (envelope-from uspoerlein@gmail.com) Received: by ug-out-1314.google.com with SMTP id 71so538154ugh for ; Fri, 13 Apr 2007 11:55:07 -0700 (PDT) DKIM-Signature: a=rsa-sha1; c=relaxed/relaxed; d=gmail.com; s=beta; h=domainkey-signature:received:received:received:received:date:from:to:cc:subject:message-id:mail-followup-to:references:mime-version:content-type:content-disposition:in-reply-to; b=p4eiaQISUVP3UMmiRAGeR1aD7g8qh2F8eMETofUQAJsoJIB2YrvT+YQsPxWeJORe28bZUOooQm6/BWhCzqNg5Nn6RDxsHekeCMqjxbXomMsXgIBDzxZwI/lQ8yLBIO7Tq9yz2hXt3JSs1gMnRqtDaCtHh+B3QLPtXC3ueLId3BA= DomainKey-Signature: a=rsa-sha1; c=nofws; d=gmail.com; s=beta; h=received:date:from:to:cc:subject:message-id:mail-followup-to:references:mime-version:content-type:content-disposition:in-reply-to; b=jCVb7yKDF7QkUpPQgw61gZ22lZ+SyEmVs40dmL4Bjy0D/ZPKoKcqnLAi3ls3DGbBPW/ccKnOxRIv3fiIitvZh7JGJe+2S9AuLsL/5PrV4k/3pNs+DALYciVeEb/3QdUdYyJNA0shqH0yX8FMoirkiiDnPVKa8PtclA0Y61mYVts= Received: by 10.82.138.6 with SMTP id l6mr4723953bud.1176490506174; Fri, 13 Apr 2007 11:55:06 -0700 (PDT) Received: from roadrunner.q.local ( [85.180.144.87]) by mx.google.com with ESMTP id j2sm1100333mue.2007.04.13.11.54.58; Fri, 13 Apr 2007 11:55:04 -0700 (PDT) Received: from roadrunner.q.local (localhost [127.0.0.1]) by roadrunner.q.local (8.13.8/8.13.8) with ESMTP id l3DIiQkx023163; Fri, 13 Apr 2007 20:44:26 +0200 (CEST) (envelope-from uspoerlein@gmail.com) Received: (from q@localhost) by roadrunner.q.local (8.13.8/8.13.8/Submit) id l3DIiPRL023159; Fri, 13 Apr 2007 20:44:25 +0200 (CEST) (envelope-from uspoerlein@gmail.com) Date: Fri, 13 Apr 2007 20:44:25 +0200 From: Ulrich Spoerlein To: "Rick C. Petty" Message-ID: <20070413184425.GA6042@roadrunner.q.local> Mail-Followup-To: "Rick C. Petty" , freebsd-fs@FreeBSD.ORG, freebsd-current@FreeBSD.ORG References: <20070406025700.GB98545@garage.freebsd.pl> <86k5wo55s0.fsf@dwp.des.no> <20070407203411.GJ8831@cicely12.cicely.de> <86wt0n3mxv.fsf@dwp.des.no> <20070411214911.GA38351@VARK.MIT.EDU> <20070412073605.GB834@turion.vk2pj.dyndns.org> <86ps6aht1i.fsf@dwp.des.no> <20070412160603.GB92079@keira.kiwi-computer.com> <20070412185159.GB95302@nowhere> <20070412195947.GA96935@keira.kiwi-computer.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20070412195947.GA96935@keira.kiwi-computer.com> Cc: freebsd-fs@FreeBSD.ORG, freebsd-current@FreeBSD.ORG Subject: Re: ZFS committed to the FreeBSD base. 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, 13 Apr 2007 18:55:08 -0000 Rick C. Petty wrote: > On Thu, Apr 12, 2007 at 01:51:59PM -0500, Craig Boston wrote: > > For something this low level my opinion is it's better to stay with > > compile time options. After all, in the above example, cmpxchg8 is a > > single machine instruction. How much overhead does it add to retrieve a > > variable from memory and check it, then jump to the correct place? > > Enough that it outweighs the benefit of using that instruction in the > > first place? > > [...] > The problem is that ZFS would be compiled (by default) to work for many > platforms, and thus a majority of systems wouldn't get the nice > optimization. Disclaimer: I have no clue what cmpxchg8 actually does, but ... We are talking about optimizing a filesystem by speeding up the necessary CPU computations. Now, whenever the CPU waits for I/O (which the ZFS threads will do plenty of times) it has literally thousands of cycles to burn. I don't see how this could possibly make ZFS any faster if it does not avoid I/O operations entirely. Ulrich Spoerlein -- "The trouble with the dictionary is you have to know how the word is spelled before you can look it up to see how it is spelled." -- Will Cuppy