Re: preempt rt in commercial use

[Nivedita Singhvi <niv@us.ibm.com>]

Armin Steinhoff wrote:

>> Determinism = capping max latencies.
> 
>   Capping max latencies doesn't help without a good real-time, event 
> driven scheduler.
> 
>   But it helps to classify real-time operatings systems as so called 
> hard or soft real-time operating systems.
> 
>   IMHO ... there is a common understanding that a RTOS can be considered 
> as a hard-reatime OS if the
>   max latency is < 15us  because it is able to server 80% (?) of all 
> hard real-time applications in the field.

At some stage this might have been a pretty good response time.
But HW improves by leaps and bounds, and what was considered "fast"
or "real-time" 25 years ago might be your average vanilla desktop
box speed of today.

So, you'd have to define _exactly_ what operation completes
in under 15us? Again, it's these kinds of ambiguities that make
this a very woollen and fuzzy way to talk about subjects and needs
which are usually very precise and critical.

If your OS can support sub-us response times for some required
operation, I expect you wnat to say that, rather than a generic
"hard RT".


>   All others are considered as soft real-time operating systems. From 
> this point of view is PREEMPT_RT Linux
>   a hard real-time OS ... if the hardware base is appropriate.

Right. Regardless of what you call it, I would want the user to
understand very clearly what the OS is capable of, and what it
is not. And whether that meets their application's needs or not.

>   BTW ... we use PREEMPT_RT Linux  as a base for our commercial 
> solft-PLC called DACHSview: http://steinhoff-automation.com/Programming.htm

Very interesting! Thanks for sharing that...

thanks,
Nivedita