Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1757541Ab0KLNpq (ORCPT ); Fri, 12 Nov 2010 08:45:46 -0500 Received: from casper.infradead.org ([85.118.1.10]:52164 "EHLO casper.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751730Ab0KLNpp convert rfc822-to-8bit (ORCPT ); Fri, 12 Nov 2010 08:45:45 -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: <1289568827.6525.411.camel@Palantir> References: <1288333128.8661.137.camel@Palantir> <1288334050.8661.150.camel@Palantir> <1289503054.2084.156.camel@laptop> <1289503883.6525.107.camel@Palantir> <1289504635.2084.179.camel@laptop> <1289568827.6525.411.camel@Palantir> Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: 8BIT Date: Fri, 12 Nov 2010 14:45:33 +0100 Message-ID: <1289569533.2084.258.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: 1588 Lines: 35 On Fri, 2010-11-12 at 14:33 +0100, Raistlin wrote: > On Thu, 2010-11-11 at 20:43 +0100, Peter Zijlstra wrote: > > > 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. > > > :-) > > > 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? > > > Tommaso already gave the best possible explanation of this! :-P > > So, trying to recap: > - using runtime/min(deadline,period) _does_ guarantee schedulability, > but also rejects schedulable situations in UP/partitioning. Quite > sure it _does_not_ guarantee schedulability in SMP/global, but > *should* enable bounded tardiness; > - using runtime/period _does_not_ guarantee schedulability nor in > UP/partitioning neither in SMP/global, but *should* enable bounded > tardiness for _both_. > Thus, all this being said, what do you want me to do? :-D runtime/min(deadline,period) sounds fine, as its more useful than runtime/period. -- 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/