Duality between PSA and CBA

In summary, we can say that Constant Bandwidth and Proportional Share give different interfaces to similar (but not equal) allocation models: the Constant Bandwidth programming model is more suited for handling real-time constraints, so the CBA is to be preferred for integrating multimedia streams in a real-time system, while PSA is closer to the classical time-sharing approach, hence a Proportional Share scheduler can be more easily integrated in a conventional operating system (ideally, all classical multimedia applications could take advantage of this method without any modification).

As shown, Constant Bandwidth provides explicit support for hard real-time execution (reserving a bandwidth $B_i = \frac{WCET_i}{T_i}$ to each hard task, or scheduling it directly with the EDF algorithm), but also Proportional Share can emulate it, at the cost of the additional overhead of dynamically rearranging the tasks' weights. Using EEVDF, a hard guarantee can be performed at the cost of guaranteeing a computation time C_i + Q.

On the other hand, Proportional Share schedulers are more flexible in partitioning the bandwidth among non-guaranteed tasks: this is useful to run non real-time applications (such as in a traditional workstation) together with multimedia ones. In this case, the notion of weight is more intuitive than the reserved bandwidth; Constant Bandwidth can emulate this, by defining B_i=F_i, T_i = Q / B_i and using non Real-Time (NRT) tasks (an NRT task is a task composed by a single, finite or infinite, job).