From owner-freebsd-current@FreeBSD.ORG Thu Aug 25 16:37:13 2005 Return-Path: X-Original-To: freebsd-current@FreeBSD.org Delivered-To: freebsd-current@FreeBSD.org Received: from mx1.FreeBSD.org (mx1.freebsd.org [216.136.204.125]) by hub.freebsd.org (Postfix) with ESMTP id 5D84D16A41F for ; Thu, 25 Aug 2005 16:37:13 +0000 (GMT) (envelope-from rwatson@FreeBSD.org) Received: from cyrus.watson.org (cyrus.watson.org [204.156.12.53]) by mx1.FreeBSD.org (Postfix) with ESMTP id 188A943D45 for ; Thu, 25 Aug 2005 16:37:13 +0000 (GMT) (envelope-from rwatson@FreeBSD.org) Received: from fledge.watson.org (fledge.watson.org [204.156.12.50]) by cyrus.watson.org (Postfix) with ESMTP id 77E0E46B86; Thu, 25 Aug 2005 12:37:12 -0400 (EDT) Date: Thu, 25 Aug 2005 17:37:12 +0100 (BST) From: Robert Watson X-X-Sender: robert@fledge.watson.org To: "Justin R. Smith" In-Reply-To: <430DF217.2020908@drexel.edu> Message-ID: <20050825173440.O16967@fledge.watson.org> References: <430DF217.2020908@drexel.edu> MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII; format=flowed Cc: freebsd-current@FreeBSD.org Subject: Re: Hyperthreading degrades performance? X-BeenThere: freebsd-current@freebsd.org X-Mailman-Version: 2.1.5 Precedence: list List-Id: Discussions about the use of FreeBSD-current List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Thu, 25 Aug 2005 16:37:13 -0000 On Thu, 25 Aug 2005, Justin R. Smith wrote: > This is in reply to the people who said this because of > cache-contention. Has anyone benchmarked this? > > There's an article > > http://www.2cpu.com/articles/41_1.html > > that benchmarks hyperthreading in Linux and shows a modest (~29%) > improvement in performance --- depending on applications (with java > showing degradation of performance). Perhaps the linux sheduler does > things differently... In in the last couple of years, I've seen some changes in how we interact with HTT. 2-3 years ago, when benchmarking MySQL with and without HTT, I saw a 30%+ drop-off when HTT was enabled. Now, they come out about the same. I previously also saw no improvement with buildkernel, but recently I've seen credible reports of build improvements when running with HTT. So I think that things have changed a bit as a result of significant scheduler improvements in the last few years, as well as reduced lock contention. A continued slight decrease in performance for some benchmarks wouldn't surprise me, but seeing more in the way of "break even" or even "improvement" strikes me as likely. A thorough revisiting of the issue would be quite useful :-). Robert N M Watson