Loop-Triggered Cache Prefetching With Minimal Training Overhead
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Solution Overview
Problem
Existing prefetching technologies consume significant circuit area and power while requiring lengthy training periods to effectively predict memory access patterns, especially for short-lived access patterns, and are not optimized for ISAs lacking explicit loop control instructions.
Innovation Solution
Utilize loop control instructions to trigger prefetch requests, reducing the need for complex training by deriving prefetch parameters directly from these instructions, such as stride, stream count, and iteration count, thereby minimizing circuit area and power consumption.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If existing prefetching techniques are used to predict memory access patterns, then prefetching accuracy is improved, but circuit area and power consumption increase significantly
Solution Approach 1:
The patent extracts and utilizes information from loop control instructions (iteration counts, loop bounds) to trigger prefetching operations. By taking out the essential loop metadata from the instruction stream and using it to drive prefetching decisions, the system achieves accurate prefetching without requiring complex training circuits or large prefetcher structures, thus resolving the contradiction between prefetching accuracy and circuit area.
Solution Approach 2:
The patent introduces loop control instructions as an intermediary between the program logic and the prefetching mechanism. These instructions serve as a mediator that carries loop metadata (iteration counts, bounds) which the prefetcher uses to generate accurate prefetch requests. This intermediary approach enables accurate prefetching without requiring complex direct analysis of memory access patterns, reducing the needed circuit area.
2Measurement precision
If existing prefetching techniques are used to predict memory access patterns, then prefetching accuracy is improved, but power consumption increases significantly
Solution Approach 1:
The patent extracts loop metadata from control instructions and uses it to drive prefetching decisions. By taking out the essential loop information (iteration counts, bounds) and using it directly to trigger prefetching, the system achieves accurate prefetching without requiring power-intensive training operations or complex prediction circuits, thus resolving the contradiction between prefetching accuracy and power consumption.
Solution Approach 2:
The patent performs preliminary extraction of loop metadata from control instructions before the actual memory access patterns need to be predicted. By having the loop information readily available from the decoded instructions, the prefetcher can immediately generate accurate prefetch requests without requiring lengthy training periods or complex real-time analysis, reducing power consumption while maintaining accuracy.
3Measurement precision
If existing prefetching techniques are used, then prefetching accuracy is improved, but training period increases
Solution Approach 1:
The patent performs preliminary extraction of loop metadata (iteration counts, bounds) from control instructions at decode time, before any training or pattern recognition is needed. This preliminary action provides the prefetcher with immediate knowledge of the access pattern structure, eliminating the need for lengthy training periods while achieving accurate prefetching from the start.
Solution Approach 2:
The loop control instructions themselves provide the necessary information for accurate prefetching through their metadata (iteration counts, bounds). The system uses this self-provided information from the program logic to drive prefetching decisions, eliminating the need for external training mechanisms or complex pattern recognition, thus achieving accurate prefetching without time loss.
4Measurement precision
If complex training mechanisms are used for prefetching, then prefetching accuracy is improved, but device complexity increases
Solution Approach 1:
The patent extracts loop metadata from control instructions and uses it to drive prefetching decisions. By taking out the essential loop information (iteration counts, bounds) and using it directly, the system achieves accurate prefetching with a simple prefetcher that doesn't require complex training mechanisms or pattern recognition circuits, thus resolving the contradiction between prefetching accuracy and device complexity.
Solution Approach 2:
The patent introduces loop control instructions as an intermediary that provides structured metadata about memory access patterns. This intermediary carries the necessary information (loop bounds, iteration counts) that the simple prefetcher uses to generate accurate prefetch requests without needing complex internal logic or training mechanisms, resolving the contradiction between accuracy and complexity.
Data Source
AI summary
An apparatus has decoding circuitry to decode instructions defined according to an instruction set architecture (ISA) support a loop control instruction providing an explicit loop presence hint indicating that a sequence of instructions to be executed includes a program loop body to be iterated. Processing circuitry performs data processing in response to the decoded instructions. Prefetch circuitry generates a prefetch request for data to be prefetched into a cache corresponding to an address predicted to be accessed by the processing circuitry in future. In response to determining that the decoding circuitry has detected the loop control instruction, the prefetch circuitry activates generation of at least one loop-control-instruction-triggered stream of prefetch requests specifying addresses predicted based on a property of at least one instruction of the program loop body whose presence is indicated by the loop control instruction.