Re: Real-Time Scheduling and Ada

[tar@sei.cmu.edu (Thomas Ralya)]

In article <1991Nov19.214910.23519@ncsu.edu>, anf@pesun.ncsu.edu (Andre N. Fred
ette) writes:
|> 
|> The primary real-time scheduling algorithms for uni-processors seem to
|> be rate-monotonic, earliest deadline, and least slack.
|> 
|> .
|> .
|> .
|> 
|> However, Ada runtime systems do not seem to support earliest deadline or
|> least slack scheduling at all.  As far as I can tell, there is no explicit 
|> support for these disciplines in Ada 9x either -- although their
|> implementation in a particular compiler is not prohibited.
|> 
|> I'd be interested in any comments on any of these ideas/statements.

I'd like to make two points that may be a paritial answer:

 1) rate monotonic scheduling and the Ada runtime model are based on fixed
    priority scheduling, while earliest deadline and least slack are viewed 
    as requiring dynamic priorities (leading to higher executive overhead).

 2) in 25 years of building real time systems, I've never heard of a real
    time system using either of the dynamic priority scheduling techniques.
    (I'm sure they're out there somewhere, but I wonder if they are in
    wide-spread use.)