Lateral Castout Targeting in Vertical Cache Hierarchies
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Solution Overview
Problem
In multiprocessor data processing systems, lateral castouts (LCOs) are typically distributed randomly, which does not optimize cache line eviction strategies based on observed data access patterns, leading to suboptimal cache management and increased access latency.
Innovation Solution
A data processing system that records communication information between vertical cache hierarchies to determine whether to perform a lateral castout of a victim cache line to another cache hierarchy instead of system memory, selecting a recipient cache based on recorded access patterns and counters tracking data access patterns to optimize cache line eviction.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If lateral castouts are distributed randomly, then the castout operation is simple to perform, but cache management efficiency deteriorates and access latency increases
Solution Approach 1:
The patent implements feedback mechanisms through counters (e.g., counter 412) that track communication patterns between cache hierarchies. The system monitors which caches frequently request data from which other caches, and uses this feedback information to intelligently select lateral castout targets, thereby improving cache management efficiency while maintaining operational simplicity
Solution Approach 2:
The system performs preliminary actions by pre-tracking and recording communication patterns between caches using counters before castout operations are needed. This advance preparation of access pattern information enables rapid, optimized decision-making during actual castout operations without adding complexity to the castout execution itself
2Quantity of substance
If victim cache line is castout to system memory, then storage capacity is sufficient, but access latency increases significantly
Solution Approach 1:
The patent introduces an intermediary cache hierarchy level between the processor and system memory. Instead of directly casting out to system memory, the victim cache line is transferred to another cache hierarchy that serves as an intermediary storage layer, maintaining faster access characteristics while providing sufficient storage capacity
Solution Approach 2:
The system adds a lateral dimension to the traditional vertical cache hierarchy by enabling cross-hierarchy castouts at the same memory level. This dimensional expansion allows cache lines to be moved laterally between caches rather than only vertically to memory, reducing access latency while maintaining storage capacity
3Measurement precision
If data access patterns are tracked and used for castout targeting, then cache management precision improves, but system complexity increases
Solution Approach 1:
The patent segments the complex task of intelligent castout targeting into manageable components: separate counters for tracking different communication patterns, distinct tracking logic for monitoring access patterns, and a decision-making mechanism that uses this segmented information. This segmentation makes the overall system more manageable and implementable
Solution Approach 2:
The system implements self-service through automated tracking and analysis of data access patterns. The counters and tracking logic automatically monitor cache communication without external intervention, and the system autonomously uses this information to make castout decisions, reducing the need for complex external control mechanisms
Data Source
AI summary
A data processing system includes system memory and a plurality of processor cores each supported by a respective one of a plurality of vertical cache hierarchies. A first vertical cache hierarchy records information indicating communication of cache lines between the first vertical cache hierarchy and others of the plurality of vertical cache hierarchies. Based on selection of a victim cache line for eviction, the first vertical cache hierarchy determines, based on the recorded information, whether to perform a lateral castout of the victim cache line to another of the plurality of vertical cache hierarchies rather than to system memory and selects, based on the recorded information, a second vertical cache hierarchy among the plurality of vertical cache hierarchies as a recipient of the victim cache line via a lateral castout. Based on the determination, the first vertical cache hierarchy performs a castout of the victim cache line.