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Gaze into the Pattern: Characterizing Spatial Patterns with Internal Temporal Correlations for Hardware Prefetching (2412.05211v1)

Published 6 Dec 2024 in cs.AR

Abstract: Hardware prefetching is one of the most widely-used techniques for hiding long data access latency. To address the challenges faced by hardware prefetching, architects have proposed to detect and exploit the spatial locality at the granularity of spatial region. When a new region is activated, they try to find similar previously accessed regions for footprint prediction based on system-level environmental features such as the trigger instruction or data address. However, we find that such context-based prediction cannot capture the essential characteristics of access patterns, leading to limited flexibility, practicality and suboptimal prefetching performance. In this paper, inspired by the temporal property of memory accessing, we note that the temporal correlation exhibited within the spatial footprint is a key feature of spatial patterns. To this end, we propose Gaze, a simple and efficient hardware spatial prefetcher that skillfully utilizes footprint-internal temporal correlations to efficiently characterize spatial patterns. Meanwhile, we observe a unique unresolved challenge in utilizing spatial footprints generated by spatial streaming, which exhibit extremely high access density. Therefore, we further enhance Gaze with a dedicated two-stage approach that mitigates the over-prefetching problem commonly encountered in conventional schemes. Our comprehensive and diverse set of experiments show that Gaze can effectively enhance the performance across a wider range of scenarios. Specifically, Gaze improves performance by 5.7\% and 5.4\% at single-core, 11.4\% and 8.8\% at eight-core, compared to most recent low-cost solutions PMP and vBerti.

Summary

  • The paper introduces Gaze, a hardware prefetcher that uses internal temporal correlations within spatial patterns to improve data prediction accuracy.
  • Experimental evaluation showed Gaze improved performance by over 11% in multi-core simulations with significantly lower hardware overhead (4.46KB) compared to other methods.
  • This approach provides insights for optimizing prefetching in data-intensive applications and suggests potential for application across the memory hierarchy or in hybrid prefetching models.

Characterizing Spatial Patterns with Internal Temporal Correlations for Hardware Prefetching

The paper "Gaze into the Pattern: Characterizing Spatial Patterns with Internal Temporal Correlations for Hardware Prefetching" by Chen et al., presented at the IEEE International Symposium on High-Performance Computer Architecture (HPCA), explores an innovative approach to hardware prefetching—a technique critically important in mitigating the memory latency that increasingly hampers modern CPU performance. Despite extensive research, hardware prefetching faces persistent challenges related to accurately predicting data access patterns while maintaining hardware simplicity.

Key Contributions and Methodology

The core proposition of this paper is Gaze, a spatial prefetcher that enhances the characterization of spatial data patterns by incorporating internal temporal correlations. Unlike conventional context-based prefetchers that rely heavily on environmental features like triggering instructions, Gaze focuses on the temporal order of initial memory accesses within a spatial footprint. This shift allows Gaze to more accurately predict data access patterns with reduced hardware overhead.

The methodology of Gaze is grounded in identifying the temporal characteristic within memory access patterns—a correlation that is often overlooked in traditional spatial locality approaches. The idea is that the order of accesses within a footprint could be predictive of future accesses in new but similar contexts. Gaze optimizes this process by leveraging only the first two access points in a memory region, which balances precision and implementation cost effectively.

In implementing Gaze, the authors propose a two-stage approach to manage spatial streaming behaviors. They address the problem of over-prefetching, a common issue when dealing with high-density footprints, by dynamically adjusting the prefetch aggressiveness. This adjustment preserves cache bandwidth and minimizes unnecessary data inflow, thus maintaining the prefetcher's efficiency in varied scenarios.

Experimental Evaluation

The paper provides a comprehensive evaluation of Gaze using diverse benchmarks from SPEC CPU2006, SPEC CPU2017, Ligra, PARSEC, and CloudSuite, along with additional industry-specific traces from QMM and graph analytics traces from GAP. In single-core experiments, Gaze outperformed other state-of-the-art prefetchers, including PMP and vBerti, by 5.7% and 5.4% respectively. In eight-core simulations, improvements scale up to 11.4% and 8.8%, demonstrating its robustness in high parallelism environments. The hardware overhead for Gaze remains low, with a total storage requirement of only 4.46KB, which is substantially less than some prior techniques.

Implications and Future Work

The proposed approach offers valuable insights into optimizing data prefetching using temporal characteristics inherent in spatial data patterns. The potential applications of Gaze extend beyond basic memory-intensive workloads; adaptive prefetching approaches like this are crucial in evolving computational frameworks, particularly as data-intensive applications such as big data analytics and machine learning continue to grow.

While Gaze is framed primarily in the context of L1D prefetching, its adaptable design suggests potential applicability to other levels of the memory hierarchy, possibly enhancing performance further with minimal architectural changes. This research also sets a promising foundation for future explorations into hybrid models that combine temporal and spatial strategies for even more efficient prefetching.

Moreover, the findings call for further investigation into dynamic granularity management where the system might adjust its retrieval scope in real-time based on workload characteristics. Such advancements could exploit even greater temporal-spatial synergies and cater to the diverse needs of next-generation computing landscapes.

Gaze provides an incremental yet critical step towards efficient and adaptive hardware prefetching, steering future architectural innovations aimed at narrowing the persistent performance gap between processing units and memory subsystems.

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