From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1031237AbXDQVxv (ORCPT ); Tue, 17 Apr 2007 17:53:51 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1031264AbXDQVxv (ORCPT ); Tue, 17 Apr 2007 17:53:51 -0400 Received: from waste.org ([66.93.16.53]:37351 "EHLO waste.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1031237AbXDQVxu (ORCPT ); Tue, 17 Apr 2007 17:53:50 -0400 Date: Tue, 17 Apr 2007 16:39:54 -0500 From: Matt Mackall To: Nick Piggin Cc: William Lee Irwin III , Peter Williams , 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] Message-ID: <20070417213954.GE11166@waste.org> 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> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20070417070155.GF1057@wotan.suse.de> User-Agent: Mutt/1.5.13 (2006-08-11) Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org 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". Which I think is quite a reasonable requirement. I'm pretty sure the stock scheduler falls short of both of these guarantees though. -- Mathematics is the supreme nostalgia of our time.