The Deadline Floor Protocol and Ada

At the 2013 IRTAW Workshop it was accepted that the Deadline Floor Protocol (DFP) has many advantaged over the Stack Resource Protocol (SRP), and that it should be incorporated into a future version of the language, and that ideally the support for SRP should be deprecated. This short position paper summarises the current status of proposed language changes that would be needed to make this happen. The context is single processor systems

Managing contention of software transactional memory in real-time systems

The foreseen evolution of chip architectures to higher number of, heterogeneous, cores, with non-uniform memory and non-coherent caches, brings renewed attention to the use of Software Transactional Memory (STM) as an alternative to lock-based synchronisation. However, STM relies on the possibility of aborting conflicting transactions to maintain data consistency, which impacts on the responsiveness and timing guarantees required by real-time systems. In these systems, contention delays must be (efficiently) limited so that the response times of tasks executing transactions are upperbounded and task sets can be feasibly scheduled. In this paper we defend the role of the transaction contention manager to reduce the number of transaction retries and to help the real-time scheduler assuring schedulability. For such purpose, the contention management policy should be aware of on-line scheduling information

Reduction of Context Switches due to Task Synchronization in Uniprocessor and Multiprocessor Platform

The problem of frequent context switches in multitasking is a real scheduling overhead which wastes extra CPU cycles, memory and causes much delay in scheduling. This paper focuses on reducing the context switches that result due to blocking when jobs are required to synchronize. The Priority Ceiling Protocol (PCP) is used to synchronize the tasks in uniprocessor as well as multiprocessor platforms. The jobs are scheduled using Earliest Deadline First (EDF) policy. The simulation results show that the context switches are reduced by about 20% on an average using our technique of avoiding context switches due to blocking

Performance comparison between the SRP and DFP synchronization protocols in MaRTE OS

The Deadline Floor Protocol (DFP) is a mutual exclusion synchronization protocol designed as an alternative to the Baker's Stack Resource Protocol (SRP) to access shared resources in a system scheduled under the Earliest Deadline First (EDF) policy. We have implemented both protocols in the real-time operating system MaRTE OS and we have compared their performance. Overall, DFP is easier to implement and performs better than SRP for the same data structure, a doubly-linked list (DLL). More significantly, there is a more efficient data structure (the binary heap) that cannot be used with SRP and outperforms the DLL with both protocols

Schedulability analysis of synchronization protocols based on overrun without payback for hierarchical scheduling frameworks revisited

In this paper, we revisit global as well as local schedulability analysis of synchronization protocols based on the stack resource policy (SRP) and overrun without payback for hierarchical scheduling frameworks based on fixed-priority preemptive scheduling (FPPS). We show that both the existing global and local schedulability analysis are pessimistic, present improved analysis, and illustrate the improvements by means of examples

Opaque analysis for resource sharing in compositional real-time systems

In this paper we propose opaque analysis methods to integrate dependent real-time components into hierarchical fixed-priority scheduled systems. To arbitrate mutually exclusive resource access between components, we consider two existing protocols: HSRP - comprising overrun with and without payback - and SIRAP. An opaque analysis allows to postpone the choice of a synchronization protocol until component integration time. First, we identify the sources of pessimism in the existing analysis techniques and we conclude that both protocols assume different models in their local analysis. In particular, the compositional analysis for overrun with payback (OWP) is not opaque and is pessimistic. The latter makes OWP expensive compared to its counter part without a payback mechanism (ONP). This paper presents an opaque and less pessimistic OWP analysis. Secondly, SIRAP requires more timing information to perform a task-level schedulability analysis. In many practical situations, however, detailed timing characteristics of tasks are hard to obtain. We introduce an opaque analysis for SIRAP using the analysis of ONP to reduce the required timing information during the local analysis. We show that the analysis for ONP cannot deem systems schedulable which are infeasible with SIRAP. The SIRAP analysis may therefore reduce the required system resources of a component by sacrificing the choice for an arbitrary synchronization protocol at system integration time

Tighter schedulability analysis of synchronization protocols based on overrun without payback for hierarchical scheduling frameworks

In this paper, we show that both global as well as local schedulability analysis of synchronization protocols based on the stack resource policy (SRP) and overrun without payback for hierarchical scheduling frameworks based on fixed-priority preemptive scheduling (FPPS) are pessimistic. We present tighter global and local schedulability analysis, illustrate the improvements of the new analysis by means of examples, and show that the improved global analysis is both uniform and sustainable. We evaluate the new global and local schedulability analysis based on an extensive simulation study and compare the results with the existing analysis

New Schedulability Analysis for MrsP

In this paper we consider a spin-based multiprocessor locking protocol, named the Multiprocessor resource sharing Protocol (MrsP). MrsP adopts a helping-mechanism where the preempted resource holder can migrate. The original schedulability analysis of MrsP carries considerable pessimism as it has been developed assuming limited knowledge of the resource usage for each remote task. In this paper new MrsP schedulability analysis is developed that takes into account such knowledge to provide a less pessimistic analysis than that of the original analysis. Our experiments show that, theoretically, the new analysis offers better (at least identical) schedulability than the FIFO non-preemptive protocol, and can outperform FIFO preemptive spin locks under systems with either intensive resource contention or long critical sections. The paper also develops analysis to include the overhead of MrsP’s helping mechanism. Although MrsP’s helping mechanism theoretically increases schedulability, our evaluation shows that this increase may be negated when the overheads of migrations are taken into account. To mitigate this, we have modified the MrsP protocol to introduce a short non-preemptive section following migration. Our experiments demonstrate that with migration cost, MrsP may not be favourable for short critical sections but provides a better schedulability than other FIFO spin-based protocols when long critical sections are applied

Investigating the Correctness and Efficiency of MrsP in Fully Partitioned Systems

MrsP is a FIFO spin-based protocol that adopts a helping mechanism, where a resource holder can migrate to a remote processor to keep executing if it is preempted. In practice, allowing resource-holding tasks to migrate can raise implementation issues and run-time corner cases. In this paper, we present an investigation of the correctness and efficiency of implementing MrsP in fully partitioned systems. We identify potential race conditions and corner cases of the protocol due to the use of migrations. Then, new facilities are proposed to pre- vent the issues and to provide more efficient resource-accessing behaviours. Finally, evaluations are performed to demonstrate the impact of the run-time issues and to testify the effect of proposed facilities