From owner-cvs-all@FreeBSD.ORG Sat Nov 10 15:21:15 2007 Return-Path: Delivered-To: cvs-all@FreeBSD.org Received: from mx1.freebsd.org (mx1.freebsd.org [IPv6:2001:4f8:fff6::34]) by hub.freebsd.org (Postfix) with ESMTP id 7FD5E16A417 for ; Sat, 10 Nov 2007 15:21:15 +0000 (UTC) (envelope-from julian@elischer.org) Received: from outE.internet-mail-service.net (outE.internet-mail-service.net [216.240.47.228]) by mx1.freebsd.org (Postfix) with ESMTP id 5822A13C48A for ; Sat, 10 Nov 2007 15:21:15 +0000 (UTC) (envelope-from julian@elischer.org) Received: from mx0.idiom.com (HELO idiom.com) (216.240.32.160) by out.internet-mail-service.net (qpsmtpd/0.40) with ESMTP; Sat, 10 Nov 2007 07:21:08 -0800 X-Client-Authorized: MaGic Cook1e X-Client-Authorized: MaGic Cook1e X-Client-Authorized: MaGic Cook1e X-Client-Authorized: MaGic Cook1e X-Client-Authorized: MaGic Cook1e X-Client-Authorized: MaGic Cook1e X-Client-Authorized: MaGic Cook1e X-Client-Authorized: MaGic Cook1e Received: from julian-mac.elischer.org (home.elischer.org [216.240.48.38]) by idiom.com (Postfix) with ESMTP id 0B8361269AB; Sat, 10 Nov 2007 07:21:08 -0800 (PST) Message-ID: <4735CC65.50400@elischer.org> Date: Sat, 10 Nov 2007 07:21:09 -0800 From: Julian Elischer User-Agent: Thunderbird 2.0.0.6 (Macintosh/20070728) MIME-Version: 1.0 To: Maxim Sobolev References: <200711081945.lA8JjKcW080540@repoman.freebsd.org> <47337724.9040108@FreeBSD.org> <47337940.6040909@root.org> <47340B74.9070004@freebsd.org> <4734B13C.6050008@root.org> <4735008D.7030600@FreeBSD.org> <20071110190555.I35816@delplex.bde.org> <47357937.6080400@FreeBSD.org> In-Reply-To: <47357937.6080400@FreeBSD.org> Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Cc: src-committers@FreeBSD.org, Bruce Evans , cvs-src@FreeBSD.org, Kris Kennaway , cvs-all@FreeBSD.org, Colin Percival , Nate Lawson Subject: Re: cvs commit: src/sys/amd64/amd64 mp_machdep.c src/sys/i386/i386 mp_machdep.c X-BeenThere: cvs-all@freebsd.org X-Mailman-Version: 2.1.5 Precedence: list List-Id: CVS commit messages for the entire tree List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Sat, 10 Nov 2007 15:21:15 -0000 Maxim Sobolev wrote: > Bruce Evans wrote: >> Off is a good default since hyperthreading seems to be a pessimization >> in most casts. > > Well, actually it all depends on workload and scheduling. I believe ULE > is expected to improve things quite a bit in scheduling department. > However, even with ol'good SCHED_BSD we measured noticeable performance > increase (15-25%) in CPU intensive real-world tasks with HTT enabled on > 2-way SMP Xeon system. It was in 2004, both CPUs and schedules should > have been improved since that time. > > -Maxim Vicor (where I used to work) noticed recently that newer systems were getting much less work done thann their older bretheren. On investigation they found that it was because the newer systems had HT turned off.. Their workload is a mix of FP and Int crunching in image processing and just happens to be the near perfect HT workload. With 2 x HT processors (4 logical processors), they could get about 3.7 times the throughput of a single processor in tests I did in 04 or so. However for most other loads HT turned out to be at best a wash and at worst a slight loss, so having it off will help the average user I think.