Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756053Ab0KKToG (ORCPT ); Thu, 11 Nov 2010 14:44:06 -0500 Received: from canuck.infradead.org ([134.117.69.58]:52360 "EHLO canuck.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754152Ab0KKToE convert rfc822-to-8bit (ORCPT ); Thu, 11 Nov 2010 14:44:04 -0500 Subject: Re: [RFC][PATCH 09/22] sched: add period support for -deadline tasks From: Peter Zijlstra To: Raistlin Cc: Ingo Molnar , Thomas Gleixner , Steven Rostedt , Chris Friesen , oleg@redhat.com, Frederic Weisbecker , Darren Hart , Johan Eker , "p.faure" , linux-kernel , Claudio Scordino , michael trimarchi , Fabio Checconi , Tommaso Cucinotta , Juri Lelli , Nicola Manica , Luca Abeni , Dhaval Giani , Harald Gustafsson , paulmck In-Reply-To: <1289503883.6525.107.camel@Palantir> References: <1288333128.8661.137.camel@Palantir> <1288334050.8661.150.camel@Palantir> <1289503054.2084.156.camel@laptop> <1289503883.6525.107.camel@Palantir> Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: 8BIT Date: Thu, 11 Nov 2010 20:43:55 +0100 Message-ID: <1289504635.2084.179.camel@laptop> Mime-Version: 1.0 X-Mailer: Evolution 2.30.3 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1642 Lines: 39 On Thu, 2010-11-11 at 20:31 +0100, Raistlin wrote: > On Thu, 2010-11-11 at 20:17 +0100, Peter Zijlstra wrote: > > On Fri, 2010-10-29 at 08:34 +0200, Raistlin wrote: > > > Make it possible to specify a period (different or equal than > > > deadline) for -deadline tasks. > > > > > I would expect it to be: > > > > runtime <= deadline <= period > > > Well, apart from that really unhappy comment/changelog, it should be > like that in the code, and if it's not, it is what I meant and I'll > change to that as soon as I can! :-) > > Since you spotted it... The biggest issue here is admission control > test. Right now this is done against task's bandwidth, i.e., > sum_i(runtime_i/period_i)<=threshold, but it is unfortunately wrong... > Or at least very, very loose, to the point of being almost useless! :-( Right, I have some recollection on that. > The more correct --in the sense that it at least yield a sufficient (not > necessary!) condition-- thing to do would be > sum_i(runtime_i/min{deadline_i,period_i})<=threshold. > > So, what you think we should do? Can I go for this latter option? I remember we visited this subject last time, but I seem to have forgotten most details. So sufficient (but not necessary) means its still a pessimistic approach but better than the one currently employed, or does it mean its optimistic and allows for unschedulable sets to be allowed in? -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/