Implementation and Evaluation of a Hardware Decentralized Synchronization Lock for MPSoCs

Each generation of shared memory Multi-Processor System-on-Chips (MPSoCs) tend to embed more and more computing units. The cores of modern MPSoCs are often grouped into clusters communicating with each other through Networks on Chip (NoCs). Having efficient scalable synchronization mechanisms is then mandatory to benefit from the high parallelism they offer.In this work we propose an innovative hardware support for synchronization locks. First of all, a non-intrusive measurement tool-chain allows us to prove a fundamental hypothesis as to optimization of the lock mechanism: although a lock may be used, at runtime, by various cores belonging to different clusters, it is often reused by the last core which has released it. Based on this observation, we provide a hardware decentralized solution to manage dynamic re-homing of locks in a dedicated memory, close to the latest access-granted core. This reduces overall access latency and network traffic in case of reuse of the lock within the same cluster.This paper presents our solution, called Lockality, and its performance evaluation on a characteristic MPSoC running on a hardware emulator. Experiments show large gains at low level (physical lock acquisition) as well as at the application level.