From owner-freebsd-questions@FreeBSD.ORG Thu Jan 15 19:31:53 2009 Return-Path: Delivered-To: freebsd-questions@freebsd.org Received: from mx1.freebsd.org (mx1.freebsd.org [IPv6:2001:4f8:fff6::34]) by hub.freebsd.org (Postfix) with ESMTP id 3EF3F1065673 for ; Thu, 15 Jan 2009 19:31:53 +0000 (UTC) (envelope-from dan@dan.emsphone.com) Received: from email1.allantgroup.com (email1.emsphone.com [199.67.51.115]) by mx1.freebsd.org (Postfix) with ESMTP id E9ABC8FC1E for ; Thu, 15 Jan 2009 19:31:52 +0000 (UTC) (envelope-from dan@dan.emsphone.com) Received: from dan.emsphone.com (dan-a.emsphone.com [199.67.51.107]) by email1.allantgroup.com (8.14.0/8.14.0) with ESMTP id n0FJVpYa047948 (version=TLSv1/SSLv3 cipher=DHE-RSA-AES256-SHA bits=256 verify=NO) for ; Thu, 15 Jan 2009 13:31:52 -0600 (CST) (envelope-from dan@dan.emsphone.com) Received: from dan.emsphone.com (smmsp@localhost [127.0.0.1]) by dan.emsphone.com (8.14.3/8.14.3) with ESMTP id n0FJVpMd077390 (version=TLSv1/SSLv3 cipher=DHE-RSA-AES256-SHA bits=256 verify=NO) for ; Thu, 15 Jan 2009 13:31:51 -0600 (CST) (envelope-from dan@dan.emsphone.com) Received: (from dan@localhost) by dan.emsphone.com (8.14.3/8.14.3/Submit) id n0FJVou4077351; Thu, 15 Jan 2009 13:31:50 -0600 (CST) (envelope-from dan) Date: Thu, 15 Jan 2009 13:31:49 -0600 From: Dan Nelson To: Michael Powell Message-ID: <20090115193147.GA61100@dan.emsphone.com> References: <496E06D1.2070706@gmail.com> <20090114181522.GB4487@aurora.oekb.co.at> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-OS: FreeBSD 7.1-STABLE User-Agent: Mutt/1.5.18 (2008-05-17) X-Virus-Scanned: ClamAV version 0.94.1, clamav-milter version 0.94.1 on email1.allantgroup.com X-Virus-Status: Clean X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-2.0.2 (email1.allantgroup.com [199.67.51.78]); Thu, 15 Jan 2009 13:31:52 -0600 (CST) X-Scanned-By: MIMEDefang 2.45 Cc: freebsd-questions@freebsd.org Subject: Re: kernel configuration X-BeenThere: freebsd-questions@freebsd.org X-Mailman-Version: 2.1.5 Precedence: list List-Id: User questions List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Thu, 15 Jan 2009 19:31:53 -0000 In the last episode (Jan 15), Michael Powell said: > Chuck Swiger wrote: > > While it is true that you can comment out all but i686 and get a > > working kernel, you will experience reduced performance. There are > > a number of low-level assembly routines (cf sys/i386/i386/support.s > > such as i586_bcopy) that are conditionalized off of I586_CPU only, > > even though they provide an advantage on i686 platforms also. > > Thank you very kindly for this info tidbit. In my ignorance I had > routinely built my kernels with only I686_CPU. Since the few boxen I > have are all downlevel every niche I can squeak out some performance > is sought after. Thanks indeed! Actually, those functions are only enabled if the CPU is truly a 586-class processor. See /sys/i386/isa/npx.c , the npx_attach() function. There is a test for cpu_class==CPUCLASS_586, while most modern CPUs are CPUCLASS_686. -- Dan Nelson dnelson@allantgroup.com