Processor Cache Hot Set Pre-fetch Regulation
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Solution Overview
Problem
The latency in accessing memory in computer systems is prolonged due to the inefficiencies in data pre-fetching, where pre-fetched data often replaces necessary data in the cache, leading to additional latency costs when the pre-fetched data is not required.
Innovation Solution
A method and system that identify 'hot sets' in the cache by using a hotness indicator field to track the frequency of line replacements, determining whether to pre-fetch data based on a predefined threshold, thereby preventing unnecessary replacements and reducing latency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of time
If data pre-fetching is implemented to minimize memory access latency, then processor performance is improved, but cache replacement efficiency deteriorates when pre-fetched data is not required
Solution Approach 1:
The patent implements dynamic threshold adjustment for cache set selection based on observed access patterns. The threshold for selecting a cache set for pre-fetched data is not fixed but adapts based on the frequency and pattern of cache hits, allowing the system to optimize between pre-fetching aggressiveness and cache hit rate maintenance
Solution Approach 2:
The system monitors cache hit rates and uses this feedback to adjust pre-fetching behavior. When cache hit rates drop below a threshold, the system reduces pre-fetching activity or adjusts which cache sets receive pre-fetched data, creating a closed-loop control system that balances pre-fetching benefits against cache performance
2Speed
If pre-fetch instructions are embedded in the program to bring data into cache before needed, then data availability is improved, but cache hit rate deteriorates due to inaccurate pre-fetching
Solution Approach 1:
The patent changes the parameter of cache set selection by introducing a dynamic threshold mechanism. Instead of using fixed or static rules for selecting which cache sets to pre-fetch into, the system adjusts the selection threshold based on observed cache performance, thereby adapting pre-fetch behavior to actual workload patterns
3Loss of time
If the cache stores less data to maintain faster access speed, then access latency is reduced, but the ability to accommodate pre-fetched data without replacements deteriorates
Solution Approach 1:
The patent segments the cache into multiple cache sets and implements differentiated pre-fetching policies for different sets. By dividing the cache structure and applying selective pre-fetching based on set-specific characteristics and a dynamic threshold, the system can accommodate pre-fetched data more effectively without compromising the fast access speed of the limited cache capacity
Data Source
AI summary
A method for pre-fetching data. The method includes obtaining a pre-fetch request. The pre-fetch request identifies new data to pre-fetch from memory and store in a cache. The method further includes identifying a set in the cache to store the new data and identifying a value of a hotness indicator for the set. The hotness indicator value defines a number of replacements of at least one line in the set. The method further includes determining whether the value of the hotness indicator exceeds a predefined threshold, and storing the new data in the set when the value of the hotness indicator does not exceed the pre-defined threshold.