On the Use of Hard and Soft Reservation Schemes in Constant Bandwidth Servers

Alexandre PassosGeorge Lima

Reservation-based scheduling has successfully been used as a suitable technique to support complex real-time systems. In particular, the Constant Bandwidth Server (CBS) is one such technique that has received special attention recently. In this paper we evaluate by extensive simulation two CBS versions, corresponding to hard and soft reservation schemes. The latter makes use of background processor time but to do so it may decrease the server priority too much. While the former circumvents this problem, it follows stricter reservation rules. Results obtained from our simulation indicate that both schemes perform equivalently in some scenarios while in several others the soft version significantly outperforms the hard one in mean response time, response time jitter and deadline miss ratio. Such results are relevant for system designers who can better subsidize their implementation decisions.

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