From owner-freebsd-current@FreeBSD.ORG Thu Aug 25 18:12:12 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 293EA16A41F for ; Thu, 25 Aug 2005 18:12:12 +0000 (GMT) (envelope-from andre@freebsd.org) Received: from c00l3r.networx.ch (c00l3r.networx.ch [62.48.2.2]) by mx1.FreeBSD.org (Postfix) with ESMTP id 07DFA43D48 for ; Thu, 25 Aug 2005 18:12:10 +0000 (GMT) (envelope-from andre@freebsd.org) Received: (qmail 53765 invoked from network); 25 Aug 2005 17:51:02 -0000 Received: from dotat.atdotat.at (HELO [62.48.0.47]) ([62.48.0.47]) (envelope-sender ) by c00l3r.networx.ch (qmail-ldap-1.03) with SMTP for ; 25 Aug 2005 17:51:02 -0000 Message-ID: <430E09F8.8090001@freebsd.org> Date: Thu, 25 Aug 2005 20:12:08 +0200 From: Andre Oppermann User-Agent: Mozilla/5.0 (Windows; U; Windows NT 5.0; en-US; rv:1.8b) Gecko/20050217 MIME-Version: 1.0 To: Robert Watson References: <430DF217.2020908@drexel.edu> <20050825173440.O16967@fledge.watson.org> In-Reply-To: <20050825173440.O16967@fledge.watson.org> Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Cc: "Justin R. Smith" , 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 18:12:12 -0000 Robert Watson wrote: > > 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 :-). Don't forget better PIV revisions with larger instruction decoder caches, better cache prefetching and branch prediction. I doubt much of the improvement is due to our SMP changes. A real test to find out whether it's our work or Intels would be to benchmark an old (pre Nacona) PIV running 5.3R and 7.0-current vs. a new one doing the same. -- Andre