From owner-freebsd-current@FreeBSD.ORG Sun Nov 7 03:07:00 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 B7A4D16A4CE; Sun, 7 Nov 2004 03:07:00 +0000 (GMT) Received: from hotmail.com (bay2-dav4.bay2.hotmail.com [65.54.246.108]) by mx1.FreeBSD.org (Postfix) with ESMTP id 9E41543D39; Sun, 7 Nov 2004 03:07:00 +0000 (GMT) (envelope-from tssajo@hotmail.com) Received: from mail pickup service by hotmail.com with Microsoft SMTPSVC; Sat, 6 Nov 2004 19:07:00 -0800 Received: from 24.24.201.219 by BAY2-DAV4.phx.gbl with DAV; Sun, 07 Nov 2004 03:06:47 +0000 X-Originating-IP: [24.24.201.219] X-Originating-Email: [tssajo@hotmail.com] X-Sender: tssajo@hotmail.com From: "Zoltan Frombach" To: "Brian Fundakowski Feldman" , References: <20041107025844.GC918@green.homeunix.org> Date: Sat, 6 Nov 2004 19:06:57 -0800 MIME-Version: 1.0 Content-Type: text/plain; format=flowed; charset="iso-8859-1"; reply-type=original Content-Transfer-Encoding: 7bit X-Priority: 3 X-MSMail-Priority: Normal X-Mailer: Microsoft Outlook Express 6.00.2900.2180 X-MimeOLE: Produced By Microsoft MimeOLE V6.00.2900.2180 Message-ID: X-OriginalArrivalTime: 07 Nov 2004 03:07:00.0477 (UTC) FILETIME=[D9572AD0:01C4C476] Subject: Re: SMP vs UP on single P4 CPU systems with hyperthreading 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: Sun, 07 Nov 2004 03:07:00 -0000 Thanks for the quick response. So I just probably stick with the UP kernel for now. Zoltan > On Sat, Nov 06, 2004 at 06:48:33PM -0800, Zoltan Frombach wrote: >> I just upgraded my system from a Pentium III to a Pentium 4 with >> hyperthreading. This is not a multiprocessor system, as I only have one >> CPU. I disabled hyperthreading in the BIOS (it is an AWARD BIOS). Then I >> installed FreeBSD 5.3-RELEASE. The first thing I've noticed in dmesg are >> the following lines: >> >> CPU: Intel(R) Pentium(R) 4 CPU 2.80GHz (2806.38-MHz 686-class CPU) >> Origin = "GenuineIntel" Id = 0xf29 Stepping = 9 >> >> Features=0xbfebfbff >> Hyperthreading: 2 logical CPUs >> >> So even though I specifically disabled hyperthreading in the BIOS, >> FreeBSD >> 5.3 still detects 2 logical CPUs. Is this by design? I guess, it is. So >> therefore my question is this: Should I compile an SMP kernel or a UP >> kernel? To make my decision more difficult, Scott Long posted recently in >> a >> message the following: "We turned off SMP on i386 and amd64 because it is >> a >> serious performance penalty for UP machines." >> >> Should I look at my single CPU system as a UP machine, as it physically >> is >> a uni processor machine. Or should I enable SMP in the kernel to take >> advantage of the "2 logical SPUs" FreeBSD detects - even when I try to >> disable this feature of the CPU in the BIOS... What is the official word >> in >> this scenario? I'd really appreciate your advice. > > It will be detected that you have the capability of using it, whether > or not you have enabled SMP. It's probably going to be no performance > gain to enable SMP, since it also requires slower locking operation to > remain safe for SMP versus what is sufficient for a UP system. > > -- > Brian Fundakowski Feldman \'[ > FreeBSD ]''''''''''\ > <> green@FreeBSD.org \ The Power to Serve! > \ > Opinions expressed are my own. > \,,,,,,,,,,,,,,,,,,,,,,\