Reconciling Real-Time and ÒFair'Ò Scheduling
TR88-024
Bill O. Gallmeister
Multiprogramming operating systems which support both 
real-time and non-real-time processes are called Ósoft-
real-time'Ò systems.  In such systems, process scheduling 
is problematic, because there are two qualitatively 
different classes of processes requiring scheduling. If the 
scheduling algorithm is designed to favor one class of 
processes, it  will probably not treat the other class of 
processes fairly.  For instance, priority-based schedulers 
are considered fair to non-real-time processes, but lead 
to unreliable real-time systems [3,2].  Conversely, 
deadline-based schedulers suffice to run real-time 
processes but will starve non-real-time processes, which 
have no deadline.

The common conception is that real-time responsiveness 
and fair multiprogramming are mutually exclusive.  I 
hold that this concept is wrong, because our concept of 
Òfairness'Ò is wrong.  I propose a unifying model of 
processes under which so-called ``real-time'' and non-
real-time'' processes are merely different instances of the 
same sort of object, with different attribute values.  
Under this unifying scheme, all processes can be treated 
fairly while still preserving real-time responsiveness.