From owner-freebsd-amd64@FreeBSD.ORG Thu Feb 8 06:19:13 2007 Return-Path: X-Original-To: freebsd-amd64@freebsd.org Delivered-To: freebsd-amd64@freebsd.org Received: from mx1.freebsd.org (mx1.freebsd.org [69.147.83.52]) by hub.freebsd.org (Postfix) with ESMTP id 97F0416A400 for ; Thu, 8 Feb 2007 06:19:13 +0000 (UTC) (envelope-from mwm-dated-1171778004.1a5f9b@mired.org) Received: from mired.org (vpn.mired.org [66.92.153.74]) by mx1.freebsd.org (Postfix) with SMTP id 3BD4113C46B for ; Thu, 8 Feb 2007 06:19:13 +0000 (UTC) (envelope-from mwm-dated-1171778004.1a5f9b@mired.org) Received: (qmail 80212 invoked by uid 1001); 8 Feb 2007 05:53:24 -0000 Received: by bhuda.mired.org (tmda-sendmail, from uid 1001); Thu, 08 Feb 2007 00:53:24 -0500 MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Transfer-Encoding: 7bit Message-ID: <17866.47828.219523.71972@bhuda.mired.org> Date: Thu, 8 Feb 2007 00:53:24 -0500 To: Michael Vince In-Reply-To: <45CAAB06.40907@thebeastie.org> References: <676973.69182.qm@web34510.mail.mud.yahoo.com> <45CAAB06.40907@thebeastie.org> X-Mailer: VM 7.17 under 21.4 (patch 20) "Double Solitaire" XEmacs Lucid X-Primary-Address: mwm@mired.org X-face: "5Mnwy%?j>IIV\)A=):rjWL~NB2aH[}Yq8Z=u~vJ`"(,&SiLvbbz2W`; h9L,Yg`+vb1>RG% *h+%X^n0EZd>TM8_IB;a8F?(Fb"lw'IgCoyM.[Lg#r\ X-Delivery-Agent: TMDA/1.1.5 (Fettercairn) From: Mike Meyer Cc: freebsd-questions@freebsd.org, freebsd-amd64@freebsd.org Subject: Re: Dual Core Or Dual CPU - What's the real difference in performance? X-BeenThere: freebsd-amd64@freebsd.org X-Mailman-Version: 2.1.5 Precedence: list List-Id: Porting FreeBSD to the AMD64 platform List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Thu, 08 Feb 2007 06:19:13 -0000 In <45CAAB06.40907@thebeastie.org>, Michael Vince typed: > Nicole Harrington wrote: > > Using FreeBSD, what is really the difference, besides > >power and ability to shove in more memory, between > >having the two seperate CPUS's? > Dual core or Quad Core CPUs performance are far better compared to more > socket CPUs since they get shared access to memory cache and reduce > memory latency/probing over AMDs hypertransport bus. Of course, it's not really that simple. For one thing, the intel quad core CPUS are two dual core chips in one package, and the two chips don't share internal resources - like cache. So any data in cache is only available to two of the four cpus; if the one of the other two cpus needs that data it'll have to go to the external bus. The AMD quad core package is similar - except they don't put the two chips in the same package, but provide a proprietary high-speed interconnect between them. Also, shared access to the memory cache means - well shared access to the memory cache and the memory behind it. Shared access raises the possibility of contention, which will slow things down. If all four CPUs get a cache miss for different data at the same time, one of them is in for a long wait. Yeah, this isn't very likely under most loads. How likely is it under yours? Generally, more processors means things will go faster until you run out of threads. However, if there's some shared resource that is the bottleneck for your load, and the resource doesn't support simultaneous access by all the cores, more cores can slow things down. Of course, it's not really that simple. Some shared resources can be managed so as to make things improve under most loads, even if they don't support simultaneous access. http://www.mired.org/consulting.html Independent Network/Unix/Perforce consultant, email for more information.