Coprocessor Prefetcher Using Store Queue Monitoring
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Solution Overview
Problem
Coprocessors often experience cache misses when accessing operand data, leading to delays and reduced performance in executing instructions, as existing prefetching technologies rely on predictive methods that may be inaccurate.
Innovation Solution
A dedicated coprocessor prefetcher that monitors the processor's store queue for coprocessor instructions and uses physical addresses generated by the processor to prefetch operand data into a shared cache, eliminating the need for predictive techniques and reducing latency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of time
If predictive prefetching methods are used, then the system can attempt to fetch data before it is needed, but the prediction accuracy is low leading to cache misses
Solution Approach 1:
The coprocessor prefetcher performs preliminary action by monitoring the processor's store queue and capturing physical addresses of coprocessor instructions before they are executed. It then issues prefetch requests to fetch operand data into the cache in advance, ensuring data is available when needed without relying on inaccurate predictions.
Solution Approach 2:
The prefetcher uses feedback from the processor's store queue to identify coprocessor instructions and their associated memory addresses. This feedback mechanism allows the prefetcher to accurately determine which data needs to be prefetched, improving reliability compared to blind predictive methods.
2Productivity
If the coprocessor waits for data from memory, then data accuracy is ensured, but execution speed decreases due to cache misses
Solution Approach 1:
The prefetcher performs preliminary data fetching by monitoring store queue entries and issuing memory access requests before the coprocessor actually needs the data. This eliminates waiting time during execution while ensuring data accuracy through proper cache protocols.
Solution Approach 2:
The prefetcher acts as an intermediary between the processor's store queue and the cache memory system. It captures addresses from the store queue, generates prefetch requests, and coordinates data transfer, thereby decoupling the coprocessor execution from direct memory access delays.
3Reliability
If a dedicated coprocessor prefetcher is implemented, then cache hits increase, but device complexity increases
Solution Approach 1:
The coprocessor prefetcher leverages existing processor structures, particularly the store queue, to perform its function. By reusing the store queue's address generation capabilities and integrating with the existing cache hierarchy, the prefetcher achieves high cache hit rates without proportionally increasing overall device complexity.
Solution Approach 2:
The prefetcher utilizes information already present in the processor's store queue (such as physical addresses of coprocessor instructions) to autonomously generate prefetch requests. This self-service approach reduces the need for additional complex control logic while maintaining high cache hit rates.
Data Source
AI summary
A prefetcher for a coprocessor is disclosed. An apparatus includes a processor and a coprocessor that are configured to execute processor and coprocessor instructions, respectively. The processor and coprocessor instructions appear together in code sequences fetched by the processor, with the coprocessor instructions being provided to the coprocessor by the processor. The apparatus further includes a coprocessor prefetcher configured to monitor a code sequence fetched by the processor and, in response to identifying a presence of coprocessor instructions in the code sequence, capture the memory addresses, generated by the processor, of operand data for coprocessor instructions. The coprocessor is further configured to issue, for a cache memory accessible to the coprocessor, prefetches for data associated with the memory addresses prior to execution of the coprocessor instructions by the coprocessor.