From owner-freebsd-current@FreeBSD.ORG Thu Apr 12 18:05:15 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 8313316A400 for ; Thu, 12 Apr 2007 18:05:15 +0000 (UTC) (envelope-from julian@elischer.org) Received: from outY.internet-mail-service.net (outY.internet-mail-service.net [216.240.47.248]) by mx1.freebsd.org (Postfix) with ESMTP id 6A38313C480 for ; Thu, 12 Apr 2007 18:05:15 +0000 (UTC) (envelope-from julian@elischer.org) Received: from mx0.idiom.com (HELO idiom.com) (216.240.32.160) by out.internet-mail-service.net (qpsmtpd/0.32) with ESMTP; Thu, 12 Apr 2007 10:34:17 -0700 Received: from [10.251.22.38] (nat.ironport.com [63.251.108.100]) by idiom.com (Postfix) with ESMTP id 75B23125AEB; Thu, 12 Apr 2007 11:05:14 -0700 (PDT) Message-ID: <461E74DA.3020402@elischer.org> Date: Thu, 12 Apr 2007 11:05:14 -0700 From: Julian Elischer User-Agent: Thunderbird 1.5.0.10 (Macintosh/20070221) MIME-Version: 1.0 To: Robert Watson References: <461E0078.3050001@cisco.com> <461E092B.4080001@cisco.com> <86d529zxci.fsf@dwp.des.no> <20070412153930.A99718@fledge.watson.org> In-Reply-To: <20070412153930.A99718@fledge.watson.org> Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 8bit Cc: Ivan Voras , Randall Stewart , freebsd-current@freebsd.org, Janardhan Iyengar , =?ISO-8859-1?Q?Dag-Erling_Sm=F8rgrav?= , Brad Penoff Subject: Re: CPU utilization 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: Thu, 12 Apr 2007 18:05:15 -0000 Robert Watson wrote: > > On Thu, 12 Apr 2007, Dag-Erling Smørgrav wrote: > >> Randall Stewart writes: >>> machdep.hyperthreading_allowed: 0 >> >> Note that enabling hyperthreading is more likely to harm performance >> than to help it. You should just disable it in the BIOS, and run a UP >> kernel. > > Historically this has been true, but some more recent results I've seen > suggest that both hyperthreading hardware has improved, and the > efficiency of our SMP implementation and scheduler has lead to it being > more effective used. I would reevaluate this on more modern hardware and > using a more recent kernel before assuming this remains true for your > application. In addition to this, to answer the original question, I remember a commit so that if you disable a cpu (or HT cpu) it doesn't get counted in the CPU % so if you have 2 cpus and disable one hten prior to that commit it was not possible to get > 50% busy but after that commit you could get 100% "of the available CPUs". That fix is not (I believe) in 6.2. I have had applications where HT was useful. They had a mix of integer and floating point work, and were long running, using all of their quanta. Usually with normal work it was a was or a loss. > > Robert N M Watson > Computer Laboratory > University of Cambridge > > > ------------------------------------------------------------------------ > > _______________________________________________ > freebsd-current@freebsd.org mailing list > http://lists.freebsd.org/mailman/listinfo/freebsd-current > To unsubscribe, send any mail to "freebsd-current-unsubscribe@freebsd.org"