Improved scheduling of generalized pinwheel task systems

Abstract

The generalized pinwheel scheduling problem is defined as follows: Given a multiset {(a/sub 1/, b/sub 1/), (a/sub 2/, b/sub 2/), ..., (a/sub n/, b/sub n/)} of ordered pairs of positive integers, determine whether there is an infinite sequence over the symbols {1, 2, 3, ..., n} such that, for each i, 1/spl les/i/spl les/n, any subsequence of b/sub i/ consecutive symbols contains at least a/sub i/ i's. Such an infinite sequence is called a schedule for the generalized pin wheel task system {(a/sub 1/, b/sub 1/), (a/sub 2/, b/sub 2/), ..., (a/sub n/, b/sub n/)}. When all the a/sub i/'s are equal to one, this problem has been previously studied as the pinwheel scheduling problem. A linear-time algorithm is presented for solving such instances which determines whether such an instance has a schedule. A fast on-line scheduler (FOLS) is also derived, which can actually generate the schedule in O(log n) time per slot given O(n) preprocessing time. When compared to traditional pinwheel scheduling algorithms, this new algorithm has a higher density threshold on a very large subclass of generalized pinwheel task systems.