A High-Frequency Load-Store Queue with Speculative Allocations for High-Level Synthesis

Szafarczyk, R., Nabi, S. W. and Vanderbauwhede, W. (2024) A High-Frequency Load-Store Queue with Speculative Allocations for High-Level Synthesis. In: International Conference on Field Programmable Technology (FPT'23), Yokohama, Japan, 11-14 December 2023, pp. 115-124. ISBN 9798350359114 (doi: 10.1109/ICFPT59805.2023.00018)

Abstract

Dynamically scheduled high-level synthesis (HLS) enables the use of load-store queues (LSQs) which can disambiguate data hazards at circuit runtime, increasing throughput in codes with unpredictable memory accesses. However, the increased throughput comes at the price of lower clock frequency and higher resource usage compared to statically scheduled circuits without LSQs. The lower frequency often nullifies any throughput improvements over static scheduling, while the resource usage becomes prohibitively expensive with large queue sizes. This paper presents a method for achieving dynamically scheduled memory operations in HLS without significant clock period and resource usage increase. We present a novel LSQ based on shift-registers enabled by the opportunity to specialize queue sizes to a target code in HLS. We show a method to speculatively allocate addresses to our LSQ, significantly increasing pipeline parallelism in codes that could not benefit from an LSQ before. In stark contrast to traditional load value speculation, we do not require pipeline replays and have no overhead on misspeculation. On a set of benchmarks with data hazards, our approach achieves an average speedup of 11× against static HLS and 5× against dynamic HLS that uses a state of the art LSQ from previous work. Our LSQ also uses several times fewer resources, scaling to queues with hundreds of entries, and supports both on-chip and off-chip memory.

• Item Type: Conference Proceedings
• Additional Information: This work was partly supported by the UK EPSRC.
• Status: Published
• Refereed: Yes
• Glasgow Author(s) Enlighten ID: Szafarczyk, Mr Robert and Nabi, Dr Syed Waqar and Vanderbauwhede, Professor Wim
• Authors: Szafarczyk, R., Nabi, S. W., and Vanderbauwhede, W.
• College/School: College of Science and Engineering > School of Computing Science
• ISSN: 2837-0449
• ISBN: 9798350359114
• Copyright Holders: Copyright © 2023 IEEE
• First Published: First published in 2023 International Conference on Field Programmable Technology (ICFPT)
• Publisher Policy: Reproduced in accordance with the publisher copyright policy

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