Hardware Prefetcher Suppression via Control Logic
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Solution Overview
Problem
Modern processors face challenges in optimizing the execution of instructions, particularly complex ones like floating-point operations and load/store operations, which can lead to inefficiencies in pipeline throughput due to hardware prefetching, causing latency and resource management issues.
Innovation Solution
The implementation of an instruction set architecture that allows for selective suppression of hardware prefetchers based on data addresses, using mechanisms like prefetch suppressor modules to control when hardware prefetchers act, thereby optimizing resource allocation and reducing latency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If hardware prefetchers are enabled to improve memory access efficiency, then cache hit rate is improved, but pipeline throughput deteriorates due to latency and resource management issues
Solution Approach 1:
The patent applies local quality by making different parts of the memory system have different prefetching behaviors. Specifically, it implements separate prefetching controls for different cache levels (L1 vs L2/L3) and different memory regions, allowing optimized prefetching where beneficial while suppressing it where harmful to pipeline throughput.
Solution Approach 2:
The patent implements dynamic control of hardware prefetchers through runtime mechanisms that can enable or disable prefetching based on current execution conditions. This includes dynamic prefetcher suppression that responds to pipeline status, memory access patterns, and resource availability, allowing the system to adapt prefetching behavior to current workload characteristics.
2Loss of time
If hardware prefetchers are activated to reduce memory access latency, then memory access efficiency is improved, but resource management deteriorates due to increased complexity
Solution Approach 1:
The patent extracts the prefetching control logic from the general memory management system and creates a separate, dedicated control mechanism. This includes extracting prefetcher suppression capabilities that can independently control prefetching behavior without interfering with other memory management functions, thereby simplifying overall resource management.
Solution Approach 2:
The patent introduces intermediary control structures that mediate between the hardware prefetchers and the memory management unit. These intermediaries include control registers, status flags, and coordination logic that manage prefetcher behavior in a standardized way, reducing the complexity burden on the main memory management system.
3Productivity
If selective suppression of hardware prefetchers is implemented based on data addresses, then pipeline throughput is enhanced, but device complexity increases due to additional control mechanisms
Solution Approach 1:
The patent segments the prefetching control into distinct functional units and address range handlers. Each segment can independently manage prefetching for specific address ranges or memory regions, allowing fine-grained control without requiring a monolithic complex control system. This modular segmentation reduces overall control complexity while enabling selective suppression.
Data Source
AI summary
A processor includes a core, a hardware prefetcher, and a prefetcher control module. The hardware prefetcher includes logic to make speculative prefetch requests, through a memory subsystem, for elements for execution by the core, and logic to store prefetched elements in a cache. The prefetcher control module includes logic to selectively suppress, based on a hardware-prefetch suppression instruction executed by the core, a speculative prefetch request to be made by the hardware prefetcher.