We propose two complementary methods to account for scheduler overhead in the schedulability analysis of Variable Bandwidth Servers (VBS), which control process execution speed by allocating variable CPU bandwidth to processes. Scheduler overhead in VBS may be accounted for either by decreasing process execution speed to maintain CPU utilization (called response accounting), or by increasing CPU utilization to maintain process execution speed (called utilization accounting). Both methods can be combined by handling an arbitrary fraction of the total scheduler overhead with one method and the rest with the other. Distinguishing scheduler overhead due to releasing and due to suspending processes allows us to further improve our analysis by accounting for releasing overhead in a separate, virtual VBS process, which increases CPU utilization less than through regular utilization accounting. The remaining overhead may then be accounted for in either more increased CPU utilization, or decreased process execution speed. Our method can readily be generalized to account for non-constant scheduler overhead, motivated by our VBS implementation, which can be configured to run (with increasing space complexity) in quadratic, linear, and constant time (in the number of processes). Although our analysis is based on the VBS model, the general idea of response and utilization accounting may also be applied to other, related scheduling methods
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