From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751922AbXDQXXv (ORCPT ); Tue, 17 Apr 2007 19:23:51 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1751965AbXDQXXv (ORCPT ); Tue, 17 Apr 2007 19:23:51 -0400 Received: from omta05ps.mx.bigpond.com ([144.140.83.195]:33274 "EHLO omta05ps.mx.bigpond.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751922AbXDQXXu (ORCPT ); Tue, 17 Apr 2007 19:23:50 -0400 Message-ID: <462556FE.6010407@bigpond.net.au> Date: Wed, 18 Apr 2007 09:23:42 +1000 From: Peter Williams User-Agent: Thunderbird 1.5.0.10 (X11/20070302) MIME-Version: 1.0 To: Matt Mackall CC: Nick Piggin , William Lee Irwin III , Mike Galbraith , Con Kolivas , Ingo Molnar , ck list , Bill Huey , linux-kernel@vger.kernel.org, Linus Torvalds , Andrew Morton , Arjan van de Ven , Thomas Gleixner Subject: Re: [Announce] [patch] Modular Scheduler Core and Completely Fair Scheduler [CFS] References: <1176619384.6222.70.camel@Homer.simpson.net> <46240F98.3020800@bigpond.net.au> <1176776941.6222.21.camel@Homer.simpson.net> <20070417034050.GD25513@wotan.suse.de> <46244A52.4000403@bigpond.net.au> <20070417042954.GG25513@wotan.suse.de> <20070417060955.GO8915@holomorphy.com> <20070417061503.GC1057@wotan.suse.de> <20070417062621.GL2986@holomorphy.com> <20070417070155.GF1057@wotan.suse.de> <20070417213954.GE11166@waste.org> In-Reply-To: <20070417213954.GE11166@waste.org> Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit X-Authentication-Info: Submitted using SMTP AUTH PLAIN at oaamta07ps.mx.bigpond.com from [58.164.138.40] using ID pwil3058@bigpond.net.au at Tue, 17 Apr 2007 23:23:47 +0000 Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Matt Mackall wrote: > On Tue, Apr 17, 2007 at 09:01:55AM +0200, Nick Piggin wrote: >> On Mon, Apr 16, 2007 at 11:26:21PM -0700, William Lee Irwin III wrote: >>> On Mon, Apr 16, 2007 at 11:09:55PM -0700, William Lee Irwin III wrote: >>>>> All things are not equal; they all have different properties. I like >>> On Tue, Apr 17, 2007 at 08:15:03AM +0200, Nick Piggin wrote: >>>> Exactly. So we have to explore those properties and evaluate performance >>>> (in all meanings of the word). That's only logical. >>> Any chance you'd be willing to put down a few thoughts on what sorts >>> of standards you'd like to set for both correctness (i.e. the bare >>> minimum a scheduler implementation must do to be considered valid >>> beyond not oopsing) and performance metrics (i.e. things that produce >>> numbers for each scheduler you can compare to say "this scheduler is >>> better than this other scheduler at this."). >> Yeah I guess that's the hard part :) >> >> For correctness, I guess fairness is an easy one. I think that unfairness >> is basically a bug and that it would be very unfortunate to merge something >> unfair. But this is just within the context of a single runqueue... for >> better or worse, we allow some unfairness in multiprocessors for performance >> reasons of course. > > I'm a big fan of fairness, but I think it's a bit early to declare it > a mandatory feature. Bounded unfairness is probably something we can > agree on, ie "if we decide to be unfair, no process suffers more than > a factor of x". > >> Latency. Given N tasks in the system, an arbitrary task should get >> onto the CPU in a bounded amount of time (excluding events like freak >> IRQ holdoffs and such, obviously -- ie. just considering the context >> of the scheduler's state machine). > > This is a slightly stronger statement than starvation-free (which is > obviously mandatory). I think you're looking for something like > "worst-case scheduling latency is proportional to the number of > runnable tasks". add "taking into consideration nice and/or real time priorities of runnable tasks". I.e. if a task is nice 19 it can expect to wait longer to get onto the CPU than if it was nice 0. > Which I think is quite a reasonable requirement. > > I'm pretty sure the stock scheduler falls short of both of these > guarantees though. > Peter -- Peter Williams pwil3058@bigpond.net.au "Learning, n. The kind of ignorance distinguishing the studious." -- Ambrose Bierce