Re: preempt rt in commercial use

[Jeff Angielski <jeff@theptrgroup.com>]

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