Efficient Architecture for RISC-V Vector Memory Access

Abstract

Vector processors frequently suffer from inefficient memory accesses, particularly for strided and segment patterns, often relying on high-overhead crossbars or large transposition buffers. This paper presents EARTH, a novel RISC-V vector memory access architecture utilizing shifting-based optimizations to streamline strided gather/scatter and segment operations. Implemented on FPGA, EARTH achieves 4x-8x speedups in strided benchmarks while simultaneously reducing hardware area by 9% and power consumption by 41% compared to conventional designs.

Report

Structured Report: Efficient Architecture for RISC-V Vector Memory Access

Key Highlights

• Novel Architecture: Introduces EARTH, an optimized architecture specifically designed to solve the critical inefficiency of strided and segment memory accesses in vector processors.
• Shifting-Based Optimization: The core innovation is the use of specialized shift networks to handle data routing between memory and registers, replacing traditional high-overhead crossbars.
• Performance Gain: Achieves substantial performance improvements, yielding a 4x to 8x speedup in benchmarks dominated by strided memory operations.
• Efficiency Gains: Demonstrates superior hardware efficiency, reducing hardware area by 9% and power consumption by 41% compared to existing conventional designs.
• Segment Solution: Eliminates the need for large, performance-degrading buffers for segment operations by providing high-performance, in-place bulk transposition.

Technical Details

• Targeted Problems: Addresses the challenges posed by strided memory access (requiring efficient gathering/scattering) and segment operations (requiring row-column transpositions).
• Strided Access Implementation: EARTH integrates specialized shift networks. These networks route coalesced data, enabling efficient gathering and scattering of elements between the cache line and registers with minimal overhead.
• Segment Operation Implementation: Segment operations utilize a shifted register bank. This design allows for direct column-wise access, facilitating the complex row-column transposition (bulk transposition) required for segments, doing so in-place and without dedicated external segment buffers.
• Development Platform: The architecture was implemented using Chisel HDL and integrated based on an open-source RISC-V vector unit.

Implications

• Advancing RISC-V Vector Computing: EARTH directly addresses one of the major performance bottlenecks in vector execution units—memory access—making the RISC-V Vector Extension (RVV) more competitive for high-performance computing (HPC) and data-intensive applications.
• Power and Area Efficiency: The significant reduction in power consumption and area makes this architecture highly desirable for power-constrained environments, such as edge devices and specialized accelerators based on RISC-V.
• Architectural Blueprint: The success of shifting-based optimizations provides a robust, low-complexity alternative to traditional expensive crossbar designs, offering a valuable blueprint for future vector processor and accelerator designers.
• Open-Source Impact: The implementation based on an open-source RISC-V unit suggests potential for rapid integration and widespread adoption within the growing RISC-V hardware ecosystem.