Processor Prefetch Cancellation for Cache Hit Redundancy
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Solution Overview
Problem
The existing methods for prefetching data, such as software and hardware prefetch, often result in extra prefetch instructions being executed, leading to increased instruction counts and reduced performance due to unnecessary data transfers between main memory and cache memory, especially when cache hits are predicted.
Innovation Solution
A processor with a cache memory system that includes an instruction holding section, a prediction section, and a deterrence section to identify and prevent the execution of extra prefetch instructions by determining whether a prefetch instruction is redundant based on cache hit predictions, thereby optimizing memory access operations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of time
If prefetch instructions are executed to fetch data from main memory to cache memory, then data availability for arithmetic operations is improved, but unnecessary prefetch instructions increase instruction count and reduce performance
Solution Approach 1:
The system performs preliminary actions by executing prefetch instructions to fetch data from main memory to cache memory before actual memory access instructions are executed. This preliminary data transfer reduces waiting time during arithmetic operations by ensuring data is already available in the faster cache memory when needed.
Solution Approach 2:
The determination section provides feedback by monitoring cache memory contents and comparing them with prefetch instruction targets. When data is already present in the cache memory, the system generates cancellation information to prevent execution of redundant prefetch instructions, thereby eliminating unnecessary operations that would increase instruction count and reduce performance.
2Speed
If prefetch instructions are executed to pre-fetch data, then memory access speed is improved, but resource consumption increases due to unnecessary data transfers
Solution Approach 1:
The system performs preliminary data transfer operations by executing prefetch instructions that move data from main memory to cache memory in advance of actual usage. This preliminary action accelerates subsequent memory access operations by retrieving data beforehand into the faster cache memory, thereby improving overall memory access speed.
Solution Approach 2:
The determination section monitors cache memory status and provides feedback to the instruction execution unit. When data is already present in the cache memory, the system generates cancellation information that prevents redundant prefetch instructions from executing, thereby eliminating unnecessary data transfers and reducing resource consumption including energy usage.
3Productivity
If the processor monitors cache memory to prevent extra prefetch instructions, then performance is improved by reducing unnecessary operations, but device complexity increases
Solution Approach 1:
The determination section continuously monitors cache memory contents and compares them with the target addresses of prefetch instructions. This feedback mechanism enables the system to identify when data is already present in the cache and generate cancellation information to prevent redundant prefetch operations, thereby improving performance by eliminating unnecessary instructions.
Solution Approach 2:
The determination section acts as an intermediary component between the instruction execution unit and the cache memory. It receives information about both the cache contents and the prefetch instructions, performs comparison operations, and generates cancellation information when redundancy is detected. This intermediary structure adds minimal complexity while enabling intelligent prefetch cancellation.
Data Source
AI summary
A device includes, a memory, and, a processor coupled to the memory, including a cache memory, and configured, to hold a memory access instruction for executing an access to the memory and a prefetch instruction for executing a prefetch to the memory, to determine whether or not data which is a subject data of the memory access instruction is held in the cache memory, and when the data is held in the cache memory and when a corresponding prefetch instruction that is a prefetch instruction corresponding to the memory access instruction is held in the processor, not to execute an execution of the corresponding prefetch instruction.