From owner-freebsd-questions@FreeBSD.ORG Wed Jan 12 20:53:01 2005 Return-Path: Delivered-To: freebsd-questions@freebsd.org Received: from mx1.FreeBSD.org (mx1.freebsd.org [216.136.204.125]) by hub.freebsd.org (Postfix) with ESMTP id 1578716A4CE for ; Wed, 12 Jan 2005 20:53:01 +0000 (GMT) Received: from parrot.aev.net (host29-15.pool8174.interbusiness.it [81.74.15.29]) by mx1.FreeBSD.org (Postfix) with ESMTP id 4C47943D39 for ; Wed, 12 Jan 2005 20:52:59 +0000 (GMT) (envelope-from ml@netfence.it) Received: from soth.ventu (adsl-ull-16-6.41-151.net24.it [151.41.6.16]) (authenticated bits=128) by parrot.aev.net (8.13.1/8.13.1) with ESMTP id j0CL3np2049228 (version=TLSv1/SSLv3 cipher=DHE-RSA-AES256-SHA bits=256 verify=OK) for ; Wed, 12 Jan 2005 22:03:56 +0100 (CET) (envelope-from ml@netfence.it) Received: from netfence.it (xanatar.ventu [10.1.2.6]) (authenticated bits=0) by soth.ventu (8.13.1/8.12.10) with ESMTP id j0CKpDp2055698 (version=TLSv1/SSLv3 cipher=DHE-RSA-AES256-SHA bits=256 verify=OK) for ; Wed, 12 Jan 2005 21:51:14 +0100 (CET) (envelope-from ml@netfence.it) Message-ID: <41E58E53.7060606@netfence.it> Date: Wed, 12 Jan 2005 21:53:39 +0100 From: Andrea Venturoli User-Agent: Mozilla/5.0 (OS/2; U; Warp 4.5; en-US; rv:1.6) Gecko/20040117 X-Accept-Language: it,en,fr,de MIME-Version: 1.0 To: freebsd-questions@freebsd.org References: <200501121049.j0CAnJQe028309@mp.cs.niu.edu> <828997113.20050112184556@wanadoo.fr> In-Reply-To: <828997113.20050112184556@wanadoo.fr> Content-Type: text/plain; charset=us-ascii; format=flowed Content-Transfer-Encoding: 7bit X-Scanned-By: MIMEDefang 2.45 Subject: Re: Hyperthreading hurts 5.3? X-BeenThere: freebsd-questions@freebsd.org X-Mailman-Version: 2.1.1 Precedence: list List-Id: User questions List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Wed, 12 Jan 2005 20:53:01 -0000 Anthony Atkielski wrote: >>From what you say and from what I've read today, it sounds like > hyperthreading comes close to providing two separate processors for > heterogenous system loads (where each hyperthread is using slightly > different processor resources at any given instant), but it may not buy > much of anything for massively parallel compute-bound work, FWIW I tried numerical computations on a P4 with HT enabled: I expected using 2 threads might give *at least slightly* better results, but I could come to the conclusion that with 1, 2 or 4 threads the performance gain (or loss) was exactly zero. (BTW, an old AMD 2000 XP+ would in any case almost outperform a P4 3GHz, but that's another story). Obviously your use (as a server) is very different, and probably the one test I have done can't expect to achieve 100% coverage even in this field... but, anyway, just my 2 cents... bye av.