From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753071AbXDQJY4 (ORCPT ); Tue, 17 Apr 2007 05:24:56 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1753075AbXDQJY4 (ORCPT ); Tue, 17 Apr 2007 05:24:56 -0400 Received: from mx2.mail.elte.hu ([157.181.151.9]:35401 "EHLO mx2.mail.elte.hu" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753049AbXDQJYz (ORCPT ); Tue, 17 Apr 2007 05:24:55 -0400 Date: Tue, 17 Apr 2007 11:24:22 +0200 From: Ingo Molnar To: William Lee Irwin III Cc: Davide Libenzi , Nick Piggin , Peter Williams , Mike Galbraith , Con Kolivas , ck list , Bill Huey , Linux Kernel Mailing List , Linus Torvalds , Andrew Morton , Arjan van de Ven , Thomas Gleixner Subject: Re: [Announce] [patch] Modular Scheduler Core and Completely Fair Scheduler [CFS] Message-ID: <20070417092422.GA19414@elte.hu> References: <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> <20070417070949.GR8915@holomorphy.com> <20070417073308.GB30559@elte.hu> <20070417090538.GU8915@holomorphy.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20070417090538.GU8915@holomorphy.com> User-Agent: Mutt/1.4.2.2i X-ELTE-VirusStatus: clean X-ELTE-SpamScore: -2.0 X-ELTE-SpamLevel: X-ELTE-SpamCheck: no X-ELTE-SpamVersion: ELTE 2.0 X-ELTE-SpamCheck-Details: score=-2.0 required=5.9 tests=BAYES_00 autolearn=no SpamAssassin version=3.1.7 -2.0 BAYES_00 BODY: Bayesian spam probability is 0 to 1% [score: 0.0000] Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org * William Lee Irwin III wrote: > [...] Also rest assured that the tone of the critique is not hostile, > and wasn't meant to sound that way. ok :) (And i guess i was too touchy - sorry about coming out swinging.) > Also, given the general comments it appears clear that some > statistical metric of deviation from the intended behavior furthermore > qualified by timescale is necessary, so this appears to be headed > toward a sort of performance metric as opposed to a pass/fail test > anyway. However, to even measure this at all, some statement of > intention is required. I'd prefer that there be a Linux-standard > semantics for nice so results are more directly comparable and so that > users also get similar nice behavior from the scheduler as it varies > over time and possibly implementations if users should care to switch > them out with some scheduler patch or other. yeah. If you could come up with a sane definition that also translates into low overhead on the algorithm side that would be great! The only good generic definition i could come up with (nice levels are isolated buckets with a constant maximum relative percentage of CPU time available to every active bucket) resulted in having a per-nice-level array of rbtree roots, which did not look worth the hassle at first sight :-) until now the main approach for nice levels in Linux was always: "implement your main scheduling logic for nice 0 and then look for some low-overhead method that can be glued to it that does something that behaves like nice levels". Feel free to turn that around into a more natural approach, but the algorithm should remain fairly simple i think. Ingo