From owner-freebsd-hackers@FreeBSD.ORG Mon Nov 26 09:36:32 2007 Return-Path: Delivered-To: freebsd-hackers@freebsd.org Received: from mx1.freebsd.org (mx1.freebsd.org [IPv6:2001:4f8:fff6::34]) by hub.freebsd.org (Postfix) with ESMTP id B30B916A418 for ; Mon, 26 Nov 2007 09:36:32 +0000 (UTC) (envelope-from rwatson@FreeBSD.org) Received: from cyrus.watson.org (cyrus.watson.org [209.31.154.42]) by mx1.freebsd.org (Postfix) with ESMTP id 8B2CB13C45A for ; Mon, 26 Nov 2007 09:36:32 +0000 (UTC) (envelope-from rwatson@FreeBSD.org) Received: from fledge.watson.org (fledge.watson.org [209.31.154.41]) by cyrus.watson.org (Postfix) with ESMTP id 056394796E; Mon, 26 Nov 2007 04:40:05 -0500 (EST) Date: Mon, 26 Nov 2007 09:36:25 +0000 (GMT) From: Robert Watson X-X-Sender: robert@fledge.watson.org To: Stephen Montgomery-Smith In-Reply-To: <20071125143546.V6583@cauchy.math.missouri.edu> Message-ID: <20071126091342.P65286@fledge.watson.org> References: <474830F9.90305@zirakzigil.org> <6eb82e0711240638g2cc1e54o1fb1321cafe8ff9f@mail.gmail.com> <1188.202.127.99.4.1195957922.squirrel@webmail.triplegate.net.id> <20071125110116.U63238@fledge.watson.org> <20071125143546.V6583@cauchy.math.missouri.edu> MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII; format=flowed Cc: binto , freebsd-hackers@freebsd.org Subject: Re: Before & After Under The Giant Lock X-BeenThere: freebsd-hackers@freebsd.org X-Mailman-Version: 2.1.5 Precedence: list List-Id: Technical Discussions relating to FreeBSD List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Mon, 26 Nov 2007 09:36:32 -0000 On Sun, 25 Nov 2007, Stephen Montgomery-Smith wrote: > (Also when I run 4 threads with 2 cpus, each with hyperthreading, it goes > 2.5 to 3 times faster - surprising since hyperthreading gets quite bad press > for its performance improvements - I should add that Linux didn't do at all > well at taking advantage of hyperthreading, running at the same speed as > with 2 threads.) I've seen gradual improvements both in our ability to manage HTT and HTT itself. One of the things that gave HTT a particularly bad reputation was that it was first introduced in the P4 Xeon CPU line from Intel, and that line had extortionately expensive synchronization instructions compared to either prior or later CPU lines. As a result, even a small amount of synchronization (read: kernel locking) quickly ate any benefits of potential parallelism. More recent CPUs have managed to reduce "extionate" to "relatively expensive", which is much more manageable. Robert N M Watson Computer Laboratory University of Cambridge