Theodore P. Baker

Stack-based scheduling for realtime processes

The Priority Ceiling Protocol (PCP) of Sha, Rajkumar and Lehoczky is a policy for locking binary semaphores that bounds priority inversion (i.e., the blocking of a job while a lower priority job executes), and thereby improves schedulability under fixed priority preemptive scheduling. We show how to extend the PCP to handle: multiunit resources, which subsume binary semaphores and reader-writer locks; dynamic priority schemes, such as earliest-deadline-first (EDF), that use static “preemption levels”; sharing of runtime stack space between jobs. These extensions can be applied independently, or together.The Stack Resource Policy (SRP) is a variant of the SRP that incorporates the three extensions mentioned above, plus the conservative assumption that each job may require the use of a shared stack. This avoids unnecessary context switches and allows the SRP to be implemented very simply using a stack. We prove a schedulability result for EDF scheduling with the SRP that is tighter than the one proved previously for EDF with a dynamic version of the PCP.The Minimal SRP (MSRP) is a slightly more complex variant of the SRP, which has similar properties, but imposes less blocking. The MSRP is optimal for stack sharing systems, in the sense that it is the least restrictive policy that strictly bounds priority inversion and prevents deadlock for rate monotone (RM) and earliest-deadline-first (EDF) scheduling.

Relativizations of the

We investigate relativized versions of the open question of whether every language accepted nondeterministically in polynomial time can be recognized deterministically in polynomial time. For any set X, let

\mathcal{P} = ?\mathcal{NP}

\mathcal{P}^X (\text{resp. }\mathcal{NP}^X )

Question

be the class of languages accepted in polynomial time by deterministic (resp. nondeterministic) query machines with oracle X. We construct a recursive set A such that

Real Time Scheduling Theory: A Historical Perspective

\mathcal{P}^A = \mathcal{NP}^A

A stack-based resource allocation policy for realtime processes

. On the other hand, we construct a recursive set B such that

Multiprocessor EDF and deadline monotonic schedulability analysis

\mathcal{P}^B \ne \mathcal{NP}^B

The cyclic executive model and Ada

. Oracles X are constructed to realize all consistent set inclusion relations between the relativized classes

Aperiodic servers in a deadline scheduling environment

\mathcal{P}^X

An analysis of EDF schedulability on a multiprocessor

,