Cache Prefetch Throttle Mechanism for Resource Efficiency
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
In processor-based systems, prefetching mechanisms often waste resources by issuing prefetch requests for data that is not subsequently used, leading to inefficiencies in cache management and increased latency due to unnecessary data copying from main memory to cache.
Innovation Solution
A method and system for throttling prefetch requests by analyzing prefetch stream history to determine which relative addresses have been accessed by previous streams, allowing only prefetch requests for addresses that have been accessed by other streams, thereby reducing unnecessary prefetching.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If prefetch requests are issued for all predicted memory addresses, then cache hit rate is improved, but system resource usage increases due to unnecessary data copying
Solution Approach 1:
The patent implements a feedback mechanism by monitoring whether prefetched data is actually accessed by the processor. A counter tracks the number of accesses to each prefetched cache line, and this information feeds back into the prefetch decision logic. When the counter indicates low utilization, subsequent prefetch requests for similar patterns are suppressed, thereby reducing wasted resources while maintaining cache effectiveness for genuinely useful prefetches.
Solution Approach 2:
The patent dynamically adjusts prefetching parameters based on observed access patterns. Specifically, it modifies the prefetch threshold and prefetch distance parameters according to the utilization metrics of previously prefetched data. This adaptive parameter adjustment allows the system to optimize between aggressive prefetching (for high-utilization patterns) and conservative prefetching (for low-utilization patterns), resolving the contradiction between cache performance and resource efficiency.
2Loss of time
If aggressive prefetching is used to populate cache lines, then average memory access latency is reduced, but cache management efficiency deteriorates due to unnecessary data copying
Solution Approach 1:
The patent enables the cache system to self-regulate its prefetching behavior by automatically monitoring the utility of prefetched data and adjusting its own prefetch decisions accordingly. The system uses the access patterns of previously prefetched data to automatically suppress future prefetch requests for similar patterns, eliminating the need for external control mechanisms and improving cache management efficiency while maintaining low latency for beneficial prefetches.
Solution Approach 2:
The patent effectively discards unprefetched or underutilized prefetch patterns by suppressing further prefetch requests for them. The system identifies prefetch patterns that result in low cache line utilization and recovers resources by stopping the wasteful copying of such data, thereby improving cache management efficiency. Meanwhile, it continues aggressive prefetching for patterns that prove useful, maintaining low memory access latency.
3Reliability
If prefetch requests are issued for all predicted addresses, then data availability in cache is improved, but performance-per-Watt decreases due to wasted energy on unused data
Solution Approach 1:
The patent applies partial prefetching by selectively issuing prefetch requests only for addresses that are likely to be useful based on monitored access patterns. Instead of prefetching all predicted addresses unconditionally, the system performs prefetching partially - only for patterns that have demonstrated utility - thereby reducing energy consumption while maintaining data availability for actually needed data.
Solution Approach 2:
The system uses feedback from access pattern monitoring to guide prefetch decisions. By tracking whether prefetched data is accessed and feeding this information back into the prefetch logic, the system learns to issue prefetch requests only when likely to be beneficial. This feedback-driven approach ensures data availability for useful prefetches while eliminating energy-wasting prefetches for unused data, thus improving performance-per-Watt.
Data Source
AI summary
The present invention provides a method and apparatus for throttling prefetch requests for a cache. One embodiment of the method includes selecting a sequence of relative addresses for prefetching data from a memory into lines of a cache in response to detecting a cache miss to a first address. The sequence of relative addresses is determined relative to the first address. This embodiment of the method also includes issuing a prefetch request for data from a memory address indicated by one of the sequence of relative addresses when at least one previous prefetch stream accessed prefetched data associated with this one of the sequence of relative addresses.