Jeff Angielski wrote:
On 09/14/2010 05:44 AM, Robert Schwebel wrote:
On Tue, Sep 14, 2010 at 11:24:21AM +0200, Raz 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.
True. But show me a single RTOS which provides a real "hard
real-time" operation. They all suffer by the SMI functions, cache
problems or other
resource constrains at hardware level ... specially when they run on
x86 hardware.
But most people/companies who think they need hard realtime really don't.
Missing a deadline by 5us is not a problem for most control
applications ... e.g. the fastes bus cycle of Profinet is today 250us.
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
Yes, more important is an extended range of priorities (up to 99) and
a clean event oriented real-time scheduling.
What we really don't need is the dual kernel concept of RT-LINUX :)
--Armin
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