Re: Why is Linux not RTOS?

["Raseel Bhagat" <raseelbhagat@gmail.com>]

Hi

On 4/5/07, Pradeep <pradeep.annavarapu@moschip.com> wrote:
>
> > Hi,
> >
> > Why is Linux kernel considered a (hard) realtime OS? I already
>
> Linux kernel is never considered a real time OS.
> A real time OS should be predictable.The general linux kernel is not
> predictable because of many reasons.

To ellaborate more, any RTOS HAS TO be deterministic , i.e, it should
have a deterministic latecy, a predictable jitter which will never
cross its threshold even during heavy loads.


> > What stops us from classifying kernel as hard RTOS? Is it because at
>
> An RTOS is just a facilitator to build Real time systems. A Real time system
> developer should analyse a RTOS wether is will be useful for his system.
> If some body is holding spin lock and making it non-preemptive its a bad
> design. So even a RTOS linux has spin locks. Its the designer who should
> take care.

Basically , a GPOS (General Purpose OS) is build to optimize the
average-response time. Whereas, an RTOS is designed to optimize the
worst-case response time. Hence non-RT tasks, in case of an RTOS , are
given the least prioirity where as the deadlines for RT tasks are not
to be crossed under ANY circumstances.

Thanks,
Raseel.
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