From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S261523AbUL3C6E (ORCPT ); Wed, 29 Dec 2004 21:58:04 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S261525AbUL3C6E (ORCPT ); Wed, 29 Dec 2004 21:58:04 -0500 Received: from mail.tmr.com ([216.238.38.203]:54214 "EHLO gaimboi.tmr.com") by vger.kernel.org with ESMTP id S261523AbUL3C57 (ORCPT ); Wed, 29 Dec 2004 21:57:59 -0500 Message-ID: <41D3713D.3010707@tmr.com> Date: Wed, 29 Dec 2004 22:08:45 -0500 From: Bill Davidsen User-Agent: Mozilla/5.0 (X11; U; Linux i686; en-US; rv:1.7) Gecko/20040616 X-Accept-Language: en-us, en MIME-Version: 1.0 To: Justin Piszcz CC: linux-kernel@vger.kernel.org Subject: Re: Kernel Benchmarks With P4+SMP+SMT? References: In-Reply-To: Content-Type: text/plain; charset=us-ascii; format=flowed Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Justin Piszcz wrote: > Has anyone performed any benchmarks with: > > No SMP w/HT? > SMP w/HT? > SMP + SMT w/HT? > > [ ] Symmetric multi-processing support > [ ] SMT (Hyperthreading) scheduler support > > x SMT scheduler support improves the CPU scheduler's decision making > x when dealing with Intel Pentium 4 chips with HyperThreading at a > x cost of slightly increased overhead in some places. If unsure say > x N here. > > I'm tempted to try SMT and benchmark these sometime but I am asking the > list if anyone has already done this first. > > Question: "slightly increased overhead in some places." > > What type of workloads would exhibit such overhead? > > Would this option (SMT) be recommended for a desktop or server machine? > > Are there any white papers or documentation I can read about this option? I run SMT on all my HT uni systems. Depending on what you do it can help up to 30% (kernel build) or just enough to measure. This is one of those "it depends" things, I bet there are loads which run better without, and there is a tad of overhead in the SMP kernel locking. If you run SMP, you have that overhead anyway, so I doubt it hurts. YMMV -- bill davidsen CTO TMR Associates, Inc Doing interesting things with small computers since 1979