Seeking time-composable partitions of tasks for COTS multicore processors

The timing verification of real-time single core systems involves a timing analysis step that yields an Execution Time Bound (ETB) for each task, followed by a schedulability analysis step, where the scheduling attributes of the individual tasks, including the ETB, are studied from the system level perspective. The transition between those two steps involves accounting for the interference effects that arise when tasks contend for access to shared resource. The advent of multicore processors challenges the viability of this two-step approach because several complex contention effects at the processor level arise that cause tasks to be unable to make progress while actually holding the CPU, which are very difficult to tightly capture by simply inflating the tasks' ETB. In this paper we show how contention on access to hardware shared resources creates a circular dependence between the determination of tasks' ETB and their scheduling at runtime. To help loosen this knot we present an approach that acknowledges different flavors of time compos ability, examining in detail the variant intended for partitioned scheduling, which we evaluate on two real processor boards used in the space domain.The research leading to this work has received funding from: the European Union’s Horizon 2020 research and innovation programme under grant agreement No 644080(SAFURE); the European Space Agency under Contract 789.2013; and COST Action IC1202, Timing Analysis On Code-Level (TACLe). This work has also been partially supported by the Spanish Ministry of Science and Innovation under grant TIN2012-34557. Jaume Abella has been partially supported by the Ministry of Economy and Competitiveness under Ramon y Cajal postdoctoral fellowship number RYC-2013-14717.Peer ReviewedPostprint (author's final draft