Re: [rtl] RTAI and RTLinux

[yodaiken@fsmlabs.com]

On Fri, Sep 01, 2000 at 04:35:26PM +0200, kissg@sztaki.hu wrote:
> I don't agree.
> The world - where the program runs - is undeterministic.
> Program must adapt itself to various circumstances including lack of
> resources. Let's say I have N message buffers in a pool. What if
> there is no more free buffer?
> Running out of memory is just a situation what the task must handle
> if necessary. This is their problem, not yours.

For me, there is a critical difference between:
Spec 1: If there are no more than N events every K time units the 
        system will never drop data.  
and
Spec 2: If total system memory demands allows, the system will never
        drop data ...

If you allocate memory from a shared dynamic pool with open 
access to that pool, then any user of system resources, or any shifts 
in even the timing of the the non-RT portion of your total system may
cause failures. 

Running out of memory is tough enough in the non-RT domain. Linux kernel
list features endless discussions on how to keep the Linux kernel floating
when there is no more space. I think it all comes down to the specification of
the system. If non-deterministic failures are ok, then dynamic memory allocation
is ok. But if non-deterministic failures are ok, why not run in the Linux domain
anyways?


-- 
---------------------------------------------------------
Victor Yodaiken 
Finite State Machine Labs: The RTLinux Company.
 www.fsmlabs.com  www.rtlinux.com