From owner-freebsd-stable@FreeBSD.ORG Mon Apr 12 14:34:30 2010 Return-Path: Delivered-To: freebsd-stable@freebsd.org Received: from mx1.freebsd.org (mx1.freebsd.org [IPv6:2001:4f8:fff6::34]) by hub.freebsd.org (Postfix) with ESMTP id 72CA91065673; Mon, 12 Apr 2010 14:34:30 +0000 (UTC) (envelope-from mdpoole@troilus.org) Received: from na3sys009aog112.obsmtp.com (na3sys009aog112.obsmtp.com [74.125.149.207]) by mx1.freebsd.org (Postfix) with SMTP id D42798FC12; Mon, 12 Apr 2010 14:34:29 +0000 (UTC) Received: from source ([74.125.92.26]) by na3sys009aob112.postini.com ([74.125.148.12]) with SMTP ID DSNKS8MvdKb/Y05wgbHji6gPlwsDP+0NOS+h@postini.com; Mon, 12 Apr 2010 07:34:30 PDT Received: by qw-out-2122.google.com with SMTP id 8so2084196qwh.43 for ; Mon, 12 Apr 2010 07:34:28 -0700 (PDT) Received: by 10.224.95.12 with SMTP id b12mr1446605qan.382.1271081218213; Mon, 12 Apr 2010 07:06:58 -0700 (PDT) Received: from graviton.troilus.org (pool-72-83-66-147.washdc.east.verizon.net [72.83.66.147]) by mx.google.com with ESMTPS id 7sm589114qwb.24.2010.04.12.07.06.56 (version=TLSv1/SSLv3 cipher=RC4-MD5); Mon, 12 Apr 2010 07:06:57 -0700 (PDT) From: Michael Poole To: Antony Mawer References: <20100412.131213.4959786962516027.chat95@mac.com> Date: Mon, 12 Apr 2010 10:06:55 -0400 In-Reply-To: (Antony Mawer's message of "Mon, 12 Apr 2010 23:58:17 +1000") Message-ID: <87tyrghiio.fsf@troilus.org> User-Agent: Gnus/5.13 (Gnus v5.13) Emacs/23.1 (gnu/linux) MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: Adrian Chadd , freebsd-stable@freebsd.org, Maho NAKATA Subject: Re: Only 70% of theoretical peak performance on FreeBSD 8/amd64, Corei7 920 X-BeenThere: freebsd-stable@freebsd.org X-Mailman-Version: 2.1.5 Precedence: list List-Id: Production branch of FreeBSD source code List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Mon, 12 Apr 2010 14:34:30 -0000 Antony Mawer writes: > This may well be the same sort of issue that was discussed in this thread here: > > http://lists.freebsd.org/pipermail/freebsd-hackers/2010-March/031004.html > > In short, the Core i7 CPUs have a feature called "TurboBoost" where > the clock speed of one or more cores is boosted when other cores are > idle and in a C2 or C3 sleep status ... if the appropriate power > saving mode isn't active on the system (which I don't think FreeBSD > does by default?), the idle cores are never put into the appropriate > power saving state, and as a result TurboBoost never kicks in... > > It _may_ be that Ubuntu configures this correctly whereas FreeBSD does > not (out of the box)? > > Of course it may be something else entirely, but worth checking out... Nakata-san's theoretical performance numbers assume 4 to 4.2 operations per core per cycle at the nominal (2.66 GHz, non-TurboBoost) clock rate. (DGEMM is double precision, but I am not familiar enough with scientific computing or with the Nehalem implementation of SSE to know why it is four operations per cycle rather than two -- is it because double precision counts as two FLOPs or is it because of multiple issue?) TurboBoost runs up to 2.93 GHz on this CPU, so it doesn't fit either the theoretical peak performance or the performance discrepancy very well. Michael Poole