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.
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.
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).