From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S262399AbTIHNlk (ORCPT ); Mon, 8 Sep 2003 09:41:40 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S262460AbTIHNlf (ORCPT ); Mon, 8 Sep 2003 09:41:35 -0400 Received: from pc1-cwma1-5-cust4.swan.cable.ntl.com ([80.5.120.4]:45186 "EHLO dhcp23.swansea.linux.org.uk") by vger.kernel.org with ESMTP id S262399AbTIHNkF (ORCPT ); Mon, 8 Sep 2003 09:40:05 -0400 Subject: Re: Scaling noise From: Alan Cox To: Pavel Machek Cc: Larry McVoy , CaT , Larry McVoy , Anton Blanchard , Linux Kernel Mailing List In-Reply-To: <20030906150817.GB3944@openzaurus.ucw.cz> References: <20030903040327.GA10257@work.bitmover.com> <20030903041850.GA2978@krispykreme> <20030903042953.GC10257@work.bitmover.com> <20030903043355.GC2019@zip.com.au> <20030903050859.GD10257@work.bitmover.com> <20030906150817.GB3944@openzaurus.ucw.cz> Content-Type: text/plain Content-Transfer-Encoding: 7bit Message-Id: <1063028321.21050.28.camel@dhcp23.swansea.linux.org.uk> Mime-Version: 1.0 X-Mailer: Ximian Evolution 1.4.4 (1.4.4-5) Date: Mon, 08 Sep 2003 14:38:42 +0100 Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org On Sad, 2003-09-06 at 16:08, Pavel Machek wrote: > Hi! > > > Maybe this is a better way to get my point across. Think about more CPUs > > on the same memory subsystem. I've been trying to make this scaling point > > The point of hyperthreading is that more virtual CPUs on same memory > subsystem can actually help stuff. Its a way of exposing asynchronicity keeping the old instruction set. Its trying to make better use of the bandwidth available by having something else to schedule into stalls. Thats why HT is really good for code which is full of polling I/O, badly coded memory accesses but is worthless on perfectly tuned hand coded stuff which doesnt stall. Its great feature is that HT gets *more* not less useful as the CPU gets faster..