From mboxrd@z Thu Jan 1 00:00:00 1970 From: Jeff Angielski Subject: Re: preempt rt in commercial use Date: Tue, 14 Sep 2010 10:49:29 -0400 Message-ID: <4C8F8B79.1010300@theptrgroup.com> References: <20100914094411.GB10841@pengutronix.de> <4C8F8500.5070002@theptrgroup.com> <201009141830.03206@zigzag.lvk.cs.msu.su> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Cc: Robert Schwebel , Raz , linux-rt-users To: "Nikita V. Youshchenko" Return-path: Received: from mail.theptrgroup.com ([71.178.251.9]:38427 "EHLO mail.theptrgroup.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754483Ab0INOtd (ORCPT ); Tue, 14 Sep 2010 10:49:33 -0400 In-Reply-To: <201009141830.03206@zigzag.lvk.cs.msu.su> Sender: linux-rt-users-owner@vger.kernel.org List-ID: On 09/14/2010 10:30 AM, Nikita V. Youshchenko wrote: >>>> anyone can say preempt rt is hard real time? >>> >>> Hard realtime has something to do with how you define "missing the >>> deadline". If somebody cuts the cable of your roboter controller in >>> the factory hall, the system misses the deadline. So it is all about >>> probabilities: hard realtime systems have a very, very low probability >>> of missing the deadline. However, in real life systems, it is> 0%. >>> >>> So yes, if you talk about real world, it is hard realtime. >> >> No. Preempt rt it's not hard realtime. >> >> But most people/companies who think they need hard realtime really >> don't. They can live with soft realtime and have a really low >> probability of missing deadlines and having long latencies. For these >> people, the preempt rt is adequate. > > Isn't any case where preempt-rt does not behave as hard reatlime a bug in > preempt-rt, that should be reported to this list and eventually fixed? That is a philosophical question for the preempt-rt maintainers. I *believe* that the design goal for the preempt rt code is to minimize kernel latency. It's not to make the kernel deterministic to support hard realtime. So I don't know if I'd call it a bug, but rather on the wish list for future enhancements. -- Jeff Angielski The PTR Group www.theptrgroup.com