Re: Why is Linux not RTOS?

["Rick Brown" <rick.brown.3@gmail.com>]

On 4/4/07, John Anthony Kazos Jr. <jakj@j-a-k-j.com> wrote:
> > Why is Linux kernel considered a (hard) realtime OS? I already
> > understand the basic reason is that the linux kernel does not
> > guarantee that a task will be completed on time. But I would
> > appreciate answers in terms of more of kernel jargons.
> >
> > What stops us from classifying kernel as hard RTOS? Is it because at
> > times the kernel is non-preemptive (for e.g. while holding spinlocks)?
> > Has it got something to do with interrupt latency / scheduling latency
> > etc?
> >
> > Is the behaviour of the kernel (when it is preemptive) similar to hard
> > real time OS ??
>
> From what I've read, the preemption in the kernel is mostly a hack because
> nobody's found a way to reduce the latency of certain long functions yet.
>
> And there is a separate RTOS version called Real-Time Linux or RTL...I
> think. Try googling. It's used in life-support machinery and so forth.

Yes, I'm aware that there are quite a lot of different patches /
projects aimed at giving better RTOS behaviour ... but my question was
aimed at vanilla kernel.

Thanks,

Rick
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