Accurately measuring contention in Mesh NoCs in time-sensitive embedded systems

Abstract

The computing capacity demanded by embedded systems is on the rise as software implements more functionalities, ranging from best-effort entertainment functions to performance-guaranteed safety-related functions. Heterogeneous manycore processors, using wormhole mesh (wmesh) Network-on-Chips (NoCs) as the main communication means, and contention block among applications, are increasingly considered to deliver the required computing performance. Most research efforts on software timing analysis have focused on deriving bounds (estimates) to the contention that tasks can suffer when accessing wmesh NoCs. However, less effort has been devoted to an equally important problem, namely, accurately measuring the actual contention tasks generate each other on the wmesh which is instrumental during system validation to diagnose any software timing misbehavior and determine which tasks are particularly affected by contention on specific wmesh routers. In this paper, we work on the foundations of contention measuring in wmesh NoCs and propose and explain the rationale of a golden metric, called task PairWise Contention (PWC). PWC allows ascribing the actual share of the contention a given task suffers in the wmesh to each of its co-runner tasks at packet level. We also introduce and formalize a Golden Reference Value (GRV) for PWC that specifically defines a criterion to fairly break down the contention suffered by a task among its co-runner tasks in the wmesh. Our evaluation shows that GRV effectively captures how contention occurs by identifying the actual core (task) causing contention and whether contention is caused by local or remote interference in the wmesh.