Real-time scheduling for media processing using conditionally guaranteed budgets

In dit proefschrift behandelen we een planningsprobleem dat haar oorsprong vindt in het kosteneffectief verwerken van verschillende media door software in consumentenapparaten, zoals digitale televisies. De laatste jaren zijn er trends gaande van analoge naar digitale systemen, en van verwerking van digitale signalen door speci??eke, toepassingsgerichte hardware naar verwerking door software. Voor de verwerking van digitale media door software wordt gebruik gemaakt van krachtige programmeerbare processoren. Om te kunnen wedijveren met bestaande oplossingen is het van belang dat deze programeerbare hardware zeer kosteneffectief wordt gebruikt. Daarnaast dienen de bestaande eigenschappen van deze consumenten apparaten, zoals robuustheid, stabiliteit, en voorspelbaarheid, behouden te blijven als er software wordt gebruikt. Verder geldt dat er gelijktijdig meerdere media stromen door een consumenten apparaat verwerkt moeten kunnen worden. Deze uitdaging is binnen de onderzoekslaboratoria van Philips aangegaan in het zogenoemde Video-Quality-of-Service programma, en het werk dat in dit proefschrift beschreven wordt is binnen dat programma ontstaan. De binnen dat programma gekozen aanpak is gebaseerd op schaalbare algoritmen voor de verwerking van media, budgetten voor die algoritmen, en software dat de instelling van die algoritmen en de grootte van de budgetten aanpast tijdens de verwerking van de media. Ten behoeve van het kosteneffectief gebruik van de programmeerbare processoren zijn de budgetten krap bemeten. Dit proefschrift geeft een uitvoerige beschrijving van die aanpak, en van een model van een apparaat dat de haalbaarheid van die aanpak aantoont. Vervolgens laten we zien dat die aanpak leidt tot een probleem wanneer er gelijktijdig meerdere stromen worden verwerkt die verschillende relatieve relevanties hebben voor de gebruiker van het apparaat. Om dit probleem op te lossen stellen we het nieuwe concept van voorwaardelijk gegarandeerde budgetten voor, en beschrijven we hoe dat concept kan worden gerealiseerd. De technieken voor het analyseren van het planningprobleem voor budgetten zijn gebaseerd op bestaande technieken voor slechtste-gevals-analyse voor periodieke real-time taken. We breiden die bestaande technieken uit met technieken voor beste-gevals-analyse zodat we apparaten die gebruik maken van dit nieuwe type budget kunnen analyseren

Converting existing analysis to the EDP resource model

In (hard) real-time embedded systems, it is necessary to guarantee that tasks always meet their deadlines i.e. results should neither be too early nor too late. In the context of fixed-priority systems, this is usually done by performing schedulability analysis in which the (best-case and) worst-case response-time of each task is computed and compared with its (best-case) worst-case deadline to determine schedulability. Resource reservation has been proposed as a means to provide temporal isolation between applications. Building upon this notion, hierarchical scheduling frameworks for different resource models have been proffered in the literature with complementary schedulability conditions. Unfortunately, these novel ideas do not directly allow for the reuse of existing results, but rather favor derivations from first principles. In this document, we investigate a means to reuse existing results from non-hierarchical scheduling theory by modeling the unavailability of a resource in a two-level hierarchical framework using two fictive tasks with highest priorities. We show that this novel method using our unavailability model not only allows for unifying the analysis but can also be easily applied in determining linear response-time upper bounds. For the latter, we also consider approaches for obtaining tighter bounds for harmonic tasks

Towards budgeting in real-time calculus : deferrable servers

Budgeting of resources is an often used solution for guaranteeing performance of lower priority tasks. In this paper, we take a formal approach to the modeling of a deferrable server budgeting strategy, using real-time calculus. We prove a scheduling theorem for deferrable servers, and as a corollary show that an earlier claim of Davis and Burns, that periodic servers dominate deferrable servers with respect to schedulability, no longer holds when the context of the comparison is slightly generalized

A new approach for global synchronization in hierarchical scheduled real-time systems

We present our ongoing work to improve an existing synchronization protocol SIRAP for hierarchically scheduled real-time systems. A less pessimistic schedulability analysis is presented which can make the SIRAP protocol more efficient in terms of calculated CPU resource needs. In addition and for the same reason, an extended version of SIRAP is proposed, which decreases the interference from lower priority tasks. The new version of SIRAP has the potential to make the protocol more resource efficient than the original one

Worst-case response time analysis of real-time tasks under fixed-priority scheduling with deferred preemption revisited

Fixed-priority scheduling with deferred preemption (FPDS) has been proposed in the literature as a viable alternative to fixed-priority preemptive scheduling (FPPS), that both reduces the cost of arbitrary preemptions and removes the need for non-trivial resource access protocols. This paper shows that existing worst-case response time analysis of hard real-time tasks under FPDS, arbitrary phasing and relative deadlines at most equal to periods is both pessimistic and optimistic. This paper provides a revised analysis, resolving the problems with the existing approaches. The analysis assumes a continuous scheduling model. It is shown that the critical instant, longest busy period, and worst-case response time for a task are suprema rather than maxima for all tasks, except for the lowest priority task. Moreover, it is shown that the analysis is not uniform for all tasks, i.e. the analysis for the lowest priority task differs from the analysis of the other tasks, because only the lowest priority task cannot be blocked. To build on earlier work, the worst-case response time analysis for FPDS is expressed in terms of known worst-case analysis results for FPPS. The paper includes pessimistic variants of the analysis, which are uniform for all tasks

Grasp : visualizing the behavior of hierarchical multiprocessor real-time systems

Trace visualization is a viable approach for gaining insight into the behavior of complex distributed real-time systems. Grasp is a versatile trace visualization toolset. This paper presents its unique visualization capabilities for hierarchical multiprocessor systems, including partitioned and global multiprocessor scheduling with migrating tasks and jobs, communication between jobs via shared memory and message passing, and hierarchical scheduling in combination with multiprocessor scheduling. Its flexible plugin infrastructure allows for easy extension with custom visualization and analysis techniques for automatic trace verification. Grasp is freely available on the web

Performance and fairness in VANETs

This paper presents performance and fairness analysis of the 802.11p Medium Access Control (MAC) in one-hop periodic broadcast V2V communication used in cooperative driving applications aimed for improving vehicle safety and traffic efficiency. We show that both performance and fairness strongly dependent on the random relative phasing (F0) of the vehicles and on the impact of Hidden Nodes (HNs)