Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S264544AbTFKWk0 (ORCPT ); Wed, 11 Jun 2003 18:40:26 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S264590AbTFKWkZ (ORCPT ); Wed, 11 Jun 2003 18:40:25 -0400 Received: from aneto.able.es ([212.97.163.22]:60651 "EHLO aneto.able.es") by vger.kernel.org with ESMTP id S264544AbTFKWkU (ORCPT ); Wed, 11 Jun 2003 18:40:20 -0400 Date: Thu, 12 Jun 2003 00:54:01 +0200 From: "J.A. Magallon" To: Artemio Cc: Linux Kernel Mailing List Subject: Re: SMP question Message-ID: <20030611225401.GE2712@werewolf.able.es> References: <200306112313.30903.artemio@artemio.net> Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Disposition: inline Content-Transfer-Encoding: 7BIT In-Reply-To: <200306112313.30903.artemio@artemio.net>; from artemio@artemio.net on Wed, Jun 11, 2003 at 22:13:30 +0200 X-Mailer: Balsa 2.0.11 Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1520 Lines: 31 On 06.11, Artemio wrote: > Hello! > > > > How much performance will I loose this way? Is SMP *THAT* critical? > > > > You will lose about half your CPU power. > > 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. -- J.A. Magallon \ Software is like sex: werewolf.able.es \ It's better when it's free Mandrake Linux release 9.2 (Cooker) for i586 Linux 2.4.21-rc7-jam1 (gcc 3.3 (Mandrake Linux 9.2 3.3-1mdk)) - 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/