On-line schedulability tests for adaptive reservations in fixed priority scheduling

RODRIGO SANTOS; GIUSEPPE LIPARI; ENRICO BINI; TOMMASO CUCINOTTA

REAL-TIME SYSTEMS

SPRINGER

Lugar: Berlin; Año: 2012 vol. 48 p. 601 - 634

0922-6443

Adaptive reservation is a real-time scheduling technique in which each application is associated a fraction of the computational resource (a reservation) that can be dynamically adapted to the varying requirements of the application by using appropriate feedback control algorithms. An adaptive reservation is typically implemented by using an aperiodic  server (e.g. sporadic server) algorithm with fixed period and variable budget. When the feedback law demands an increase of the reservationbudget, the system must run a schedulability test to check if there is enough spare bandwidth to accommodate such increase. The  schedulability test must be very fast, as it may be performed at each budget update, i.e. potentially at each instance of a task; yet, it must be as efficient as possible, to maximize resource usage.In this paper, we tackle the problem of performing an efficient on-line schedulability test for adaptive resource reservations in fixed priority schedulers. In the literature, a number of algorithms have been proposed for on-line admission control in fixed priority systems. We describe four of these tests, with increasing complexity and performance. In addition, we propose a novel on-line test, called Spare-Pot algorithm, which has been specifically designed for the problem at hand, and whichshows a good cost/performance ratio compared to the other tests.