Branch Opcode Memory Prefetching to Reduce Cache Miss Stalls
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Solution Overview
Problem
Existing memory prefetching techniques in information processing systems, particularly for bulk memory, suffer from excessive latency and processor stalls due to the lack of instruction-based prefetching, leading to inefficient management of memory access times.
Innovation Solution
Implementing a batch memory prefetching mechanism that includes an instruction sequencer to detect branch opcodes and a prefetcher to anticipate and retrieve program instructions, using a prefetch buffer and cache replacement policies to optimize prefetching efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of time
If traditional memory prefetching is used without instruction-based detection, then the memory access latency is reduced to some extent, but processor stalls still occur due to inability to anticipate branch instructions
Solution Approach 1:
The system performs preliminary detection of branch opcodes in prefetch buffer lines before actual execution. When a branch opcode is detected, the system anticipates potential target addresses and prefetched those instructions in advance, ensuring they are ready before the processor needs them, thus eliminating stalls while maintaining low latency
Solution Approach 2:
The system implements feedback by monitoring branch opcode detections and using this information to dynamically adjust prefetching behavior. The detection of branch instructions provides feedback that triggers anticipatory prefetching of target addresses, creating a closed-loop system that adapts to actual program execution patterns and prevents processor stalls
2Reliability
If batch memory prefetching with instruction sequencer is implemented, then processor stalls are reduced through anticipatory prefetching, but device complexity increases due to additional components
Solution Approach 1:
The system merges the instruction sequencer functionality with the existing prefetcher and bulk memory interface. The instruction sequencer is integrated into the prefetch path, allowing it to detect branch opcodes and trigger anticipatory prefetching without requiring completely separate hardware structures. This consolidation reduces the overall device complexity compared to having entirely independent components
Solution Approach 2:
The prefetch buffer lines serve multiple functions: they store both regular program instructions and branch opcode information for detection. The same infrastructure is used for both traditional prefetching and the new instruction-based anticipatory prefetching, making the system multi-functional and reducing the need for additional dedicated structures
3Productivity
If anticipatory prefetching based on branch opcodes is used, then system performance is enhanced through reduced execution delays, but manufacturing precision requirements increase for accurate opcode detection
Solution Approach 1:
The system applies local quality by focusing opcode detection only on specific critical elements within the prefetch buffer lines - specifically the branch opcode fields. Rather than requiring high-precision processing of entire instruction streams, the system selectively monitors and detects only the relevant branch instruction patterns, reducing overall precision requirements while maintaining effective anticipatory prefetching
Data Source
AI summary
Aspects of the disclosure are directed to batch memory prefetching. In accordance with one aspect, the disclosure includes examining a current cache line from a plurality of cache lines; determining if a conditional branch opcode or an unconditional branch opcode is present; sending an anticipatory address to a bulk memory to fetch one or more anticipatory program instructions; and depositing the one or more anticipatory program instructions into a prefetch cache memory to augment an initial set of program instructions.