The Power of Virtual Time for Multimedia Scheduling

Many multimedia scheduling algorithms implement fair sharing of the CPU among processes. However, often a share of the CPU does not adequately satisfy the timing constraints of applications such as MPEG video. Several schedulers have been proposed to address this problem; each provides CPU shares but also features innovative uses of virtual time to better support multimedia applications. To give the reader a flavor of the work in this area, we first compare the mechanisms by which the SMART, BERT, and BVT algorithms provide better multimedia performance. Second, and more significantly, we propose a design methodology for producing multimedia schedulers with provable realtime behaviors using virtual time. Virtual time abstracts critical information from a complex mathematical description of the ideal system. This information is then used to schedule tasks so that the system conforms to its ideal description in real time. Virtual time is a bridge between theory and code, and this is its power.