From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S262784AbTL2HCn (ORCPT ); Mon, 29 Dec 2003 02:02:43 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S262788AbTL2HCm (ORCPT ); Mon, 29 Dec 2003 02:02:42 -0500 Received: from mail-04.iinet.net.au ([203.59.3.36]:916 "HELO mail.iinet.net.au") by vger.kernel.org with SMTP id S262784AbTL2HCl (ORCPT ); Mon, 29 Dec 2003 02:02:41 -0500 Message-ID: <3FEFD18D.3070608@cyberone.com.au> Date: Mon, 29 Dec 2003 18:02:37 +1100 From: Nick Piggin User-Agent: Mozilla/5.0 (X11; U; Linux i686; en-US; rv:1.4) Gecko/20030827 Debian/1.4-3 X-Accept-Language: en MIME-Version: 1.0 To: Pavel Machek CC: Con Kolivas , linux kernel mailing list Subject: Re: [PATCH] 2.6.0 batch scheduling, HT aware References: <200312231138.21734.kernel@kolivas.org> <20031226225652.GE197@elf.ucw.cz> <200312271042.55989.kernel@kolivas.org> <20031227110903.GA1413@elf.ucw.cz> In-Reply-To: <20031227110903.GA1413@elf.ucw.cz> Content-Type: text/plain; charset=us-ascii; format=flowed Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Pavel Machek wrote: >Hi! > > >>>BTW this is going to be an issue even on normal (non-HT) >>>systems. Imagine memory-bound scientific task on CPU0 and nice -20 >>>memory-bound seti&home at CPU1. Even without hyperthreading, your >>>scientific task is going to run at 50% of speed and seti&home is going >>>to get second half. Oops. >>> >>>Something similar can happen with disk, but we are moving out of >>>cpu-scheduler arena with that. >>> >>>[I do not have SMP nearby to demonstrate it, anybody wanting to >>>benchmark a bit?] >>> >>This is definitely the case but there is one huge difference. If you have >>2x1Ghz non HT processors then the fastest a single threaded task can run is >>at 1Ghz. If you have 1x2Ghz HT processor the fastest a single threaded task >>can run is 2Ghz. >> > >Well, gigaherz is not the *only* important thing. > >On 2x1GHz, 2GB/sec RAM bandwidth, fastest a single threaded task can >run is 1GHz, 2GB/sec. If you run two of them, it is 1GHz, >*1*GB/sec. So you still have effect similar to hyperthreading. And >yes, it can be measured. > Hi Pavel, Sure this might be a real problem sometimes, but I don't see the CPU scheduler ever handling it unless we want to add a few kitchen sinks to its nice lean code as well. If the need really arises, then probably a userspace daemon could do it.