Energy-Efficient Hardware-Accelerated Synchronization for Shared-L1-Memory Multiprocessor Clusters

Abstract

This paper proposes a light-weight Hardware-Accelerated Synchronization and Communication Unit (SCU) designed for shared-L1-memory multiprocessor clusters operating under energy-efficient near-threshold computing (NTC) conditions. Integrated into an eight-core RISC-V cluster, the SCU significantly minimizes synchronization overhead, a critical factor limiting parallel system utilization. The solution yields synchronization-free regions as small as 42 cycles (a 41x improvement over L1 test-and-set baseline) and demonstrates up to 98% energy efficiency gains on real-life DSP applications.

Report

Key Highlights

• Innovation: A light-weight Hardware-Accelerated Synchronization and Communication Unit (SCU) is introduced to accelerate PE-to-PE communication.
• Target Application: High-performance, highly power- and energy-constrained processing systems, specifically shared-L1-memory multiprocessor clusters utilizing parallel Near-Threshold Computing (NTC).
• Validation Platform: An eight-core cluster of RISC-V processors.
• Performance Gain: Synchronization-free regions are achieved in just 42 cycles, a 41x speedup compared to the baseline L1 test-and-set implementation.
• Application Results: The SCU improves performance by up to 92% (23% on average) and energy efficiency by up to 98% (39% on average) across real-life DSP applications.

Technical Details

• Architecture: The core component is the Synchronization and Communication Unit (SCU), a specialized hardware block designed for tightly-coupled clusters.
• Integration Feature: The SCU design enables fine-grain per-Processing Element (PE) power management, contributing to overall energy efficiency.
• Implementation Technology: The eight-core cluster was fabricated in advanced 22nm FDX (Fully Depleted Silicon on Insulator) technology.
• Baseline Comparison: The performance gains are measured against a traditional software-based synchronization method using fast test-and-set access to the shared L1 memory.

Implications

• Advancing RISC-V Clusters: This work solidifies the viability of using tightly-coupled RISC-V clusters with shared L1 memory as an architecture for high-GOPS/W devices. By solving the inter-core synchronization bottleneck, it maximizes the effective utilization of available RISC-V PEs.
• NTC Viability: The SCU is critical for maintaining high performance in Near-Threshold Computing (NTC) systems. NTC inherently offers high energy benefits, but synchronization overheads often negate these gains; the hardware acceleration ensures that the intended computational efficiency (over 100 GOPS/W) can actually be reached.
• IoT and Edge Computing: The massive boost in energy efficiency (up to 98%) makes this solution extremely relevant for power-sensitive domains like IoT end-nodes and edge computing devices, where low latency synchronization is crucial for real-time DSP workloads.