From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S263298AbTL2Msd (ORCPT ); Mon, 29 Dec 2003 07:48:33 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S263310AbTL2Msd (ORCPT ); Mon, 29 Dec 2003 07:48:33 -0500 Received: from gprs214-59.eurotel.cz ([160.218.214.59]:28032 "EHLO amd.ucw.cz") by vger.kernel.org with ESMTP id S263298AbTL2Msa (ORCPT ); Mon, 29 Dec 2003 07:48:30 -0500 Date: Mon, 29 Dec 2003 13:49:14 +0100 From: Pavel Machek To: Nick Piggin Cc: Con Kolivas , linux kernel mailing list Subject: Re: [PATCH] 2.6.0 batch scheduling, HT aware Message-ID: <20031229124914.GA317@elf.ucw.cz> References: <200312231138.21734.kernel@kolivas.org> <20031226225652.GE197@elf.ucw.cz> <200312271042.55989.kernel@kolivas.org> <20031227110903.GA1413@elf.ucw.cz> <3FEFD18D.3070608@cyberone.com.au> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <3FEFD18D.3070608@cyberone.com.au> X-Warning: Reading this can be dangerous to your mental health. User-Agent: Mutt/1.5.4i Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org 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. Why is it a problem? If you are handling HT case, anyway, it should be fairly easy to say "imagine it is HT system, not SMP one", and poof, problem magically goes away. Pavel /* * .----~~| * \ | * ~~~~~~ */ [Ready-made kitchen-sink for scheduler :-)))] -- When do you have a heart between your knees? [Johanka's followup: and *two* hearts?]