Re: Ada Microkernel?

["Marin David Condic" <marin.condic.auntie.spam@pacemicro.com>]

I'm not an expert, nor do I play one on TV, (NDIPOOTV?) but here's why I
think there would be a problem with marking a process "Non-Time-Slicing":
Suppose you want your process to do a run until blocked kind of thing.
Suppose the rest of the world wants to timeslice. The timeslice thing is
going to require some sort of setting of a clock/interrupt/timer that will
stop your run-until-blocked process to give control to the scheduler. The
secheduler may look and say "Ted's job is still the most important thing to
do" and give you back the processor, but in the mean time, you've been
interrupted and had control given to the OS for some duration. even if the
duration is predictable, its still undsirable because it takes time from you
and may happen at A Bad Time(tm). What may be a bigger problem is that once
that timer goes off and the scheduler gets invoked, you probably aren't
going to be able to tell in advance how long its going to be before you get
to run again. Non-determinism is definitely A Bad Thing(tm). It for sure
would shoot Rate Monotonic right square between the eyes.

I'm not sure I could see a way around not having the timer go off at regular
intervals unless you came up with some way of masking the interrupts until
you got blocked. But having blocked and enabling the interrupts so others
could round-robin, you're back with the problem of a non-deterministic delay
when you do block. This is *probably* A Bad Thing if you were counting - for
example - on your blocking operation taking a fixed & deterministic amount
of time so you don't periodically blow your timing budget.

I'm *reasonably* persuaded that the only way you could do it would be to say
at boot time - or via some privileged command - "I want to operate Realtime"
and let the GUI window apps' performance suck in exchange for the guarantees
you need from an RTOS. Since people are doing essentially this to get
realtime work done under Windows, it would seem like A Good Thing(tm) to
build right in from the start.

MDC
--
Marin David Condic
Senior Software Engineer
Pace Micro Technology Americas    www.pacemicro.com
Enabling the digital revolution
e-Mail:    marin.condic@pacemicro.com
Web:      http://www.mcondic.com/


"Ted Dennison" <dennison@telepath.com> wrote in message
news:4J0%6.1684$Kf3.17425@www.newsranger.com...
>
> I was thinking you ought to be able to somehow mark a process as "non
> time-slicing" or somesuch so that it could be scheduled along with normal
user
> processes, but still be realtime. Any real-time process is probably going
to be
> higher-priority than a user process, but it could still use the same
scheduler
> this way. But I'm not an expert in this field, so I'm guessing there may
be some
> instrinsic problems I don't see.
>