Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S264759AbTFLFyd (ORCPT ); Thu, 12 Jun 2003 01:54:33 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S264760AbTFLFyd (ORCPT ); Thu, 12 Jun 2003 01:54:33 -0400 Received: from h2.prohosting.com.ua ([217.106.231.81]:17282 "EHLO h2.prohosting.com.ua") by vger.kernel.org with ESMTP id S264759AbTFLFya (ORCPT ); Thu, 12 Jun 2003 01:54:30 -0400 From: Artemio To: "J.A. Magallon" Subject: Re: SMP question Date: Thu, 12 Jun 2003 08:37:40 +0300 User-Agent: KMail/1.5 Cc: Linux Kernel Mailing List References: <200306112313.30903.artemio@artemio.net> <20030611225401.GE2712@werewolf.able.es> In-Reply-To: <20030611225401.GE2712@werewolf.able.es> MIME-Version: 1.0 Content-Type: text/plain; charset="iso-8859-1" Content-Transfer-Encoding: 7bit Content-Disposition: inline Message-Id: <200306120837.40421.artemio@artemio.net> X-AntiAbuse: This header was added to track abuse, please include it with any abuse report X-AntiAbuse: Primary Hostname - h2.prohosting.com.ua X-AntiAbuse: Original Domain - vger.kernel.org X-AntiAbuse: Originator/Caller UID/GID - [0 0] / [0 0] X-AntiAbuse: Sender Address Domain - artemio.net Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1505 Lines: 41 Hello! Thanks for your reply! > > Hmmm... So, you mean uni-processor Linux kernel can't see two processors > > as one "big" processor? > > No, but it will work as if it does...explain below. > > You have 2 processor packages, each one is HyperThreading capable. This > means you have two 'CPUs' inside each package, so that sums up your 4 CPUs. > But there is a flaw. The 2 'CPUs' inside each processor package are not > full real CPUs, just two register sets that share cache, FP units, integer > units and so on. So let's say your Xeon has 8 FP units, and you want to > run a FPU intensive task with low or null disk IO. If you activate > hyperthreading each of the 2 'cpus' has 4 FP units, so half the computation > power. If you deactivate HT, you have 1 CPU with 8 FP units. > > In short, for FP intensive tasks, hyperthreading is a big lie... > You can't run 2 computations in parallel. Thanks for such in-depth explanation! As I understood, with HT enabled, Linux-SMP sees four CPUs with 5000 bogo mips each (of course I've already seen this in /proc/cpuinfo). So, if I deactivate HT, will a UP Linux see one CPU with 4x5000=20000 bogo mips? Anyway, I will try what I mentioned on that machine today. Thank you again and good luck! Artemio. - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/