From owner-freebsd-questions@FreeBSD.ORG Thu Feb 8 16:48:12 2007 Return-Path: X-Original-To: freebsd-questions@freebsd.org Delivered-To: freebsd-questions@freebsd.org Received: from mx1.freebsd.org (mx1.freebsd.org [69.147.83.52]) by hub.freebsd.org (Postfix) with ESMTP id 0498E16A400 for ; Thu, 8 Feb 2007 16:48:09 +0000 (UTC) (envelope-from mwm-keyword-freebsdquestions.8c5a2e@mired.org) Received: from mired.org (vpn.mired.org [66.92.153.74]) by mx1.freebsd.org (Postfix) with SMTP id 9F75B13C49D for ; Thu, 8 Feb 2007 16:48:08 +0000 (UTC) (envelope-from mwm-keyword-freebsdquestions.8c5a2e@mired.org) Received: (qmail 89226 invoked by uid 1001); 8 Feb 2007 16:49:01 -0000 Received: by bhuda.mired.org (tmda-sendmail, from uid 1001); Thu, 08 Feb 2007 11:49:01 -0500 MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Transfer-Encoding: 7bit Message-ID: <17867.21629.224092.189457@bhuda.mired.org> Date: Thu, 8 Feb 2007 11:49:01 -0500 To: Cy Schubert In-Reply-To: <200702081518.l18FIeMR002991@cwsys.cwsent.com> References: <17866.47828.219523.71972@bhuda.mired.org> <200702081518.l18FIeMR002991@cwsys.cwsent.com> 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-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: Thu, 08 Feb 2007 16:48:12 -0000 In <200702081518.l18FIeMR002991@cwsys.cwsent.com>, Cy Schubert typed: > In message <17866.47828.219523.71972@bhuda.mired.org>, Mike Meyer writes: > > 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. > > Generally speaking the performance increase is not linear. At some point > there is no benefit to adding more processors. When some other resources becomes the bottleneck. Which resource depends on the workload. In some cases, adding processors will slow things down. > To add another dimension to this discussion, hyperthreading uses spare > cycles in a single processor to pretend there are two processors, > increasing performance for some apps and reducing performance for other > apps. I think hyperthreading gets a bad rap. It shares lots of resources - like the computing units - so there are lots of workloads that cause things to get worse when you add a processor. But the general case should still be that it gets faster. > Generally speaking, dual core is an inexpensive way to get SMP into the > hands of people who could not normally afford SMP technology as it was. Gee, I thought it was a reaction to losing the clock rate war. http://www.mired.org/consulting.html Independent Network/Unix/Perforce consultant, email for more information.