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Date: Thu, 11 Nov 2010 20:43:55 +0100 From: Peter Zijlstra <peterz@...radead.org> To: Raistlin <raistlin@...ux.it> Cc: Ingo Molnar <mingo@...e.hu>, Thomas Gleixner <tglx@...utronix.de>, Steven Rostedt <rostedt@...dmis.org>, Chris Friesen <cfriesen@...tel.com>, oleg@...hat.com, Frederic Weisbecker <fweisbec@...il.com>, Darren Hart <darren@...art.com>, Johan Eker <johan.eker@...csson.com>, "p.faure" <p.faure@...tech.ch>, linux-kernel <linux-kernel@...r.kernel.org>, Claudio Scordino <claudio@...dence.eu.com>, michael trimarchi <trimarchi@...is.sssup.it>, Fabio Checconi <fabio@...dalf.sssup.it>, Tommaso Cucinotta <cucinotta@...up.it>, Juri Lelli <juri.lelli@...il.com>, Nicola Manica <nicola.manica@...i.unitn.it>, Luca Abeni <luca.abeni@...tn.it>, Dhaval Giani <dhaval@...is.sssup.it>, Harald Gustafsson <hgu1972@...il.com>, paulmck <paulmck@...ux.vnet.ibm.com> Subject: Re: [RFC][PATCH 09/22] sched: add period support for -deadline tasks 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@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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