Online Admission Test for Real-Time Tasks with Arrival Curves for Server Platforms

Centralised servers can provide on-demand resources to edge devices for offloading workloads. Resource-constrained computing nodes send requests to execute a task on the server for higher quality or faster execution. These requests are best characterised by an arrival curve. A server may become overloaded if too many requests come at once. For safety-critical applications, therefore, an admission test is required to ensure that the admitted requests meet their timing requirements.<br/>In this work, we present an online admission test to decide whether an incoming request can meet its timing requirements on a server without jeopardising the timing requirements of already admitted requests and itself, considering potential future requests to higher-priority tasks. The server executes tasks using a non-preemptive global fixed-priority scheduling policy. Our admission test extracts arrival times of future higher-priority jobs from their arrival curves and past observations and uses these, together with a reachability-based response-time analysis, to obtain a safe bound on the worst-case response time of the incoming request.<br/>Our empirical evaluations show that our admission test is effective, admitting more than of the incoming jobs to a 4- or 8-core server, when there are 20 tasks in the system. Comparing our admission test with an exact task-level schedulability test for tasks with arrival curves shows that the number of rejected admissible requests is small. The runtime of our test is practical for online analysis (typically below 6 microseconds).