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SubjectRe: [OFFTOPIC] Is Linux a Realtime-os?
John Alvord wrote:
>
> Rreal-time OS means that you can schedule tasks and they will be performed
> at the time requested with a very small margin for error. That is not
> Linux. There a Linux patch (largeish) called RTLiux which adds that
> facility. Of course the tasks are not normal linux processes...

A real time OS is an OS that allows you to use the hardware to the
limits!
The road to the limits often involves modification of the OS it self (to
fit
custom needs). If you do not have the source code - this road is
blocked.
By this definition Linux is one of the few properly field tested RT
OS's around. (do not take this too literally :-)

A custom "need" may be to deal with signal processing where algorithms
do not
tolerate 1-2 usec of interruptions*. E.g., cache flushes, bus
contention and page table invalidation's are your enemies here - you
can't deal with this efficiently and you have to resort to such exotic
and expensive stuff as "real" signal processors in environments where
you really should use that nice dual PIII with KNI as it is standing
there anyway for
various reasons.

In some areas, Linux with minor kernel hacks and creative user level
hacks,
fits the RT OS "glove" sooo nicely! It is simply amazingly funny to
instrument a modern PC
and push it to its hardware limits wrt RT using linux as the platform.
Linux can accommodate "general purpose" and "heavily customized" under
one hood
very nicely indeed ...

Ove

* essentially means that you must lock _processors_ to specific tasks

--
Ove Ewerlid
Ove.Ewerlid@syscon.uu.se or Ove.Ewerlid@signal.uu.se
Phone: +46 70 666 23 63, Fax: +46 18 503 611, +46 18 555 096

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