Register File Prefetch from L1 Cache to Cut Load Latency
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Solution Overview
Problem
Existing processor technologies face performance bottlenecks due to high latency in accessing register files, which are typically implemented using Static Random-Access Memory (SRAM), and existing prefetching techniques have primarily focused on memory-to-cache operations, neglecting the potential for reducing register file latency.
Innovation Solution
Implementing Register File Prefetch (RFP) operations from Level 1 cache to the Register File, using predicted addresses to prefetch load data directly into the register file, with mechanisms to check for address matches and bypass caches when necessary, and employing both software and hardware solutions to manage bandwidth and prefetch requests.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of time
If register file is implemented using SRAM, then data storage capability is provided, but access latency is high causing performance bottlenecks
Solution Approach 1:
The system performs preliminary prefetching of data from L1 cache to the register file using predicted addresses before the actual load instruction executes. This advance data preparation reduces the effective latency by having data ready in the register file when needed, directly addressing the time loss issue while maintaining processor performance.
2Loss of time
If prefetching is performed from L1 cache to register file, then load operation latency is reduced, but bandwidth consumption increases
Solution Approach 1:
The system changes the parameter of data location by moving data from L1 cache to register file through prefetching. This parameter change (data position) reduces access latency while the selective nature of the prefetch (using address prediction and matching) controls bandwidth consumption by only transferring necessary data.
Solution Approach 2:
The system uses feedback mechanisms where the load instruction's predicted address is compared with the prefetched data's address. This feedback loop ensures that prefetching operations are effective and bandwidth is not wasted on unnecessary data transfers, balancing latency reduction with energy efficiency.
3Measurement precision
If address prediction is used for prefetching, then prefetch accuracy improves, but complexity of address matching increases
Solution Approach 1:
The system introduces an intermediary address matching stage that compares predicted addresses with actual load addresses. This intermediary mechanism enables accurate prefetching by validating address predictions while managing the complexity through a dedicated comparison unit rather than integrating it throughout the entire processor architecture.
Data Source
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AI summary
Techniques relating to register file prefetch are described. In an embodiment, execution circuitry causes issuance of a prefetch request to copy data from a data cache unit to a register file. Other embodiments are also disclosed and claimed.