Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S264997AbTFLUpy (ORCPT ); Thu, 12 Jun 2003 16:45:54 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S264993AbTFLUpy (ORCPT ); Thu, 12 Jun 2003 16:45:54 -0400 Received: from aneto.able.es ([212.97.163.22]:44690 "EHLO aneto.able.es") by vger.kernel.org with ESMTP id S265000AbTFLUpw (ORCPT ); Thu, 12 Jun 2003 16:45:52 -0400 Date: Thu, 12 Jun 2003 22:59:31 +0200 From: "J.A. Magallon" To: Scott Robert Ladd Cc: Linux Kernel Mailing List Subject: Re: SMP question Message-ID: <20030612205931.GA3796@werewolf.able.es> References: <200306112313.30903.artemio@artemio.net> <20030611225401.GE2712@werewolf.able.es> <3EE887FA.90008@coyotegulch.com> Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Disposition: inline Content-Transfer-Encoding: 7BIT In-Reply-To: <3EE887FA.90008@coyotegulch.com>; from coyote@coyotegulch.com on Thu, Jun 12, 2003 at 16:02:34 +0200 X-Mailer: Balsa 2.0.11 Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1435 Lines: 26 On 06.12, Scott Robert Ladd wrote: > J.A. Magallon wrote: > > In short, for FP intensive tasks, hyperthreading is a big lie... > > You can't run 2 computations in parallel. > > Yes and no; the benefit of HT depends on the application in question. > I've seen everything from a 5% LOSS in performance to a 30% INCREASE in > performance, for intensive floating-point code. This is with programs > parallelized with OpenMP and Intel's C and Fortran compilers. I'm still > analyzing the exact nature of the benefits, but they *do* exist. > > While I much prefer multiple physical CPUs to "virtual" CPUs, HT *does* > provide performance improvements for certain applications. To call HT a > "big lie" is both provacative and inaccurate. > I told that because non-techical people just think they are buying _two_ processors, but they really pay too much for 1.25 processors, and that if you fine-tune your code... -- 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-rc8-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/