From owner-freebsd-current@FreeBSD.ORG Sun Nov 7 02:49:00 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 C7C6116A4CE for ; Sun, 7 Nov 2004 02:49:00 +0000 (GMT) Received: from hotmail.com (bay2-dav9.bay2.hotmail.com [65.54.246.113]) by mx1.FreeBSD.org (Postfix) with ESMTP id B2A3943D31 for ; Sun, 7 Nov 2004 02:49:00 +0000 (GMT) (envelope-from tssajo@hotmail.com) Received: from mail pickup service by hotmail.com with Microsoft SMTPSVC; Sat, 6 Nov 2004 18:49:00 -0800 Received: from 24.24.201.219 by BAY2-DAV9.phx.gbl with DAV; Sun, 07 Nov 2004 02:48:24 +0000 X-Originating-IP: [24.24.201.219] X-Originating-Email: [tssajo@hotmail.com] X-Sender: tssajo@hotmail.com From: "Zoltan Frombach" To: Date: Sat, 6 Nov 2004 18:48:33 -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 02:49:00.0459 (UTC) FILETIME=[55997FB0:01C4C474] Subject: 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 02:49:00 -0000 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. Zoltan