Multiple servers and capacity sharing for implementing flexible scheduling

The aperiodic server scheduling mechanism (like the Deferrable Server or Sporadic Server) is an adequate technique to provide service for soft and firm tasks in flexible environments. For handling multiple sources of events either a single server or multiple servers can be used. A single server minimizes the number of capacity exhaustions but provides a poor performance when the sources have different temporal requirements. This problem can be solved using multiple servers at different priorities, however this approach suffers from much more capacity exhaustions as the capacity has to be statically partitioned among them. We overcome these two problems by introducing the capacity sharing protocol in which a server can use the unused capacity of other servers. In this paper, we describe the protocol, evaluate its performance in comparison with single and multiple servers without capacity sharing and we analyze its implementation complexity. The results of the simulation analysis show that the capacity sharing protocol exhibits a better performance than single server and multiple servers without capacity sharing.