NEELPROS: A predictable real-time kernel layer design for multimedia.

摘要

New multimedia applications e.g. teleconferencing, video-on-demand, Internet telephony, etc. are revolutionizing every aspect of our life. These applications demand real-time performance, better digital signal processing, elaborate multimedia communication protocols, and faster networks and platforms.; Traditionally the embedded software to support multimedia applications is developed in a custom way. The software is fine-tuned in several iterations to get the needed real-time performance. This approach has several drawbacks: tedious design which is even more difficult for multiprocessors; lack of flexibility, as a minor change in specification may necessitate a total redesign; slower response to asynchronous events, degrading the system's real-time performance. In contrast, a kernel or operating system approach allows a more flexible software development. In the presence of a kernel layer, application writers need not worry about the task coordination, or careful timing of the events. Since the underlying software for multimedia is of embedded nature, a complex general-purpose operating system like Unix would be inappropriate. So, we architect a lean kernel layer that enhances real-time support for multimedia.; One crucial requirement for the real-time support of a system is to increase the predictability in the system. So, while architecting the different subsystems of the layer, we have attempted at increasing the predictability in the system. For scheduling, we separate out the unpredictable external events, from the synchronous computation or communication. Having one scheduling scheme for all three makes a system more unpredictable than it needs to be. This resulted in a novel approach of heterogeneous scheduling scheme with functional separation of control flow, data flow, and computation in contrast with conventional spatial hierarchical scheduling schemes. When designing the real-time communication and synchronization primitives, using the profile information, we have provided hints via constructs like real-time semaphores to increase the predictability in the system. Being in embedded domain, we do not emphasize on real-time support for memory management, though do provide special notions of region-based management and callback routines. We made our kernel customizable with a service table that allows to plug-in a custom set of scheduling, synchronization, or memory management schemes. A theoretical model for the scheduling scheme is provided, with two algorithms to operate on it. A comparative empirical study was performed on the scheduling scheme and related alternate schemes. The study found that two hybrid schemes, with good mix of the basic schemes, provide good combination of load resiliency, and functional separation.