From owner-freebsd-questions@FreeBSD.ORG Tue May 23 01:48:17 2006 Return-Path: X-Original-To: questions@freebsd.org Delivered-To: freebsd-questions@FreeBSD.ORG Received: from mx1.FreeBSD.org (mx1.freebsd.org [216.136.204.125]) by hub.freebsd.org (Postfix) with ESMTP id 81C3516A4C6 for ; Tue, 23 May 2006 01:48:17 +0000 (UTC) (envelope-from mikhailg@webanoide.org) Received: from cayster.site5.com (cayster.multisite.site5.com [216.118.97.189]) by mx1.FreeBSD.org (Postfix) with ESMTP id 1097843D48 for ; Tue, 23 May 2006 01:48:16 +0000 (GMT) (envelope-from mikhailg@webanoide.org) Received: from ppp110-20.lns1.hba1.internode.on.net ([150.101.110.20] helo=[192.168.0.4]) by cayster.site5.com with esmtpa (Exim 4.52) id 1FiM0M-0004ix-Cm; Mon, 22 May 2006 21:48:14 -0400 Message-ID: <447269DA.6040108@webanoide.org> Date: Tue, 23 May 2006 11:48:10 +1000 From: Mikhail Goriachev Organization: Webanoide User-Agent: Thunderbird 1.5.0.2 (Macintosh/20060308) MIME-Version: 1.0 To: Jon Falconer References: In-Reply-To: X-Enigmail-Version: 0.94.0.0 Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit X-Antivirus-Scanner: This message has been scanned by ClamAV. X-AntiAbuse: This header was added to track abuse, please include it with any abuse report X-AntiAbuse: Primary Hostname - cayster.site5.com X-AntiAbuse: Original Domain - freebsd.org X-AntiAbuse: Originator/Caller UID/GID - [0 0] / [47 12] X-AntiAbuse: Sender Address Domain - webanoide.org X-Source: X-Source-Args: X-Source-Dir: Cc: questions@freebsd.org Subject: Re: machdep.hlt_logical_cpus being ignored 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: Tue, 23 May 2006 01:48:17 -0000 Jon Falconer wrote: > Greetings All, > > I have installed FreeBSD 6.1 Release on a Dell 2850. I is has two Xeon > CPUs. Seeing the comment in the SMP man page about hyperthreading being a > problem in some situations, I added "machdep.hlt_logical_cpus=1" in > /boot/loader.conf file. Upon rebooting, the system still finds four CPUs > and starts all of them. I would have expected it to start only the two > physical CPUs. Am I missunderstanding what machdep.hlt_logical_cpus is > supposed to do? Should I even be concerned about the hyperthreading > problem. This system will be an email server for a small college campus > with about 2000 active accounts. > > Also, the man page for SMP say that the machdep.hlt_cpus can be used to > halt a specific CPU. I have not set this value, but sysctl shows it has a > value of 10, even before I set the machdep.hlt_logical_cpus to 1. Why > would this be the default value? I would think this would mean that one of > the system CPUs is halted. But dmesg output claims it launched four CPUs. > > Can someone fill me in on what this all means? Hi, This issue has been addressed in: http://security.freebsd.org/advisories/FreeBSD-SA-05:09.htt.asc You could also read this: http://www.daemonology.net/hyperthreading-considered-harmful/ I hope this helps. Cheers, Mikhail. -- Mikhail Goriachev Webanoide Telephone: +61 (0)3 62252501 Mobile Phone: +61 (0)4 38255158 E-Mail: mikhailg@webanoide.org Web: http://www.webanoide.org PGP Key ID: 0x4E148A3B PGP Key Fingerprint: D96B 7C14 79A5 8824 B99D 9562 F50E 2F5D 4E14 8A3B