Time/Utility Function Decomposition
in Soft Real-Time Distributed Systems
April 2004
E. Douglas Jensen, The MITRE Corporation
ABSTRACT
We consider RealTime CORBA 2.0 (Dynamic Scheduling) distributable
threads, whose time constraints are specified using time/utility functions
(TUFs), operating in legacy environments. In legacy environments, system
node resources—both physical (processor, disk, I/O, etc.) and
logical (locks, etc.)—are shared among time-critical distributable
threads and local applications that may or may not be time-critical.
Thus, in such environments, distributable threads that are scheduled
using their propagated TUFs and scheduling parameters, as mandated by
Real-Time CORBA 2.0's Case 2 approach, may suffer performance degradation,
if a node scheduler can achieve higher local accrued utility by giving
higher eligibility to local threads than to distributable threads. To
alleviate this, we consider decomposing TUFs of distributable threads
into "subTUFs" that are used for scheduling segments of
distributable threads. We present methods for decomposing TUFs. Furthermore,
we identify conditions under which TUF decomposition can alleviate performance
degradation. Our experimental results reveal that the most important
factors that affect the performance of TUF decomposition include the
properties of node scheduling algorithms, TUF shapes, task load,
Global Slack Factor, local threads and resource dependencies,
and that these factors interact.
Additional Search Keywords
realtime distributed systems, time/utility functions, realtime scheduling,
soft realtime systems, time constraint decomposition, realtime CORBA
|
