Set-Associative Cache Replacement for Equal-Priority Victim Selection
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Solution Overview
Problem
Existing cache replacement policies in set associative caches often lead to performance limitations due to cache access conflicts when selecting victim cache entries, particularly in workloads where multiple cache entries have equal priority for eviction, leading to parallel accesses targeting the same cache way and reducing overall performance.
Innovation Solution
Implement a set-specific selection criterion for selecting victim cache entries based on a preferred way that differs between sets, using cache replacement selection values to favor eviction from specific ways within each set, reducing the likelihood of cache conflicts and enabling parallel access.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If a conventional cache replacement policy is used to select victim cache entries, then the cache can maintain simple replacement logic, but cache access conflicts increase and performance deteriorates
Solution Approach 1:
The patent applies local quality by assigning different preferred ways to different sets within the cache. Each set has a designated preferred way that is favored during victim selection, creating localized differentiation without requiring complex global policies. This resolves the contradiction by introducing targeted complexity only where needed (in set-specific preferred way assignment) while maintaining simplicity in the overall replacement mechanism.
Solution Approach 2:
The patent changes the parameter of victim selection criteria by introducing set-specific preferred way indicators. Instead of using a uniform replacement policy across all cache sets, the system modifies the selection parameters to favor specific ways within each set, thereby reducing conflicts and improving performance without requiring complete policy redesign.
2Productivity
If multiple cache entries with equal priority are selected for eviction, then the replacement policy remains simple, but parallel access conflicts increase
Solution Approach 1:
The patent resolves this contradiction by introducing local differentiation through set-specific preferred ways. When multiple entries have equal priority, the system doesn't treat them uniformly but instead applies local quality preferences within each set to break ties, enabling parallel accesses to target different ways and avoiding conflicts while maintaining simple equal-priority handling.
Solution Approach 2:
The patent introduces asymmetry by designating specific ways as preferred for each set, creating an asymmetric selection bias that breaks symmetry among equal-priority entries. This asymmetric preference structure enables parallel accesses to naturally distribute across different ways, improving efficiency without complicating the victim selection process.
3Productivity
If the same cache way is targeted for multiple parallel accesses, then the replacement policy is straightforward, but access conflicts reduce system performance
Solution Approach 1:
The patent addresses this contradiction by implementing local quality through set-specific preferred way designations. This creates localized preferences that guide parallel accesses away from conflicting ways within each set, thereby reducing access conflicts and improving system efficiency without requiring complex conflict resolution mechanisms.
Solution Approach 2:
The patent applies preliminary action by pre-establishing preferred way designations for each set before cache replacements occur. This preliminary configuration guides the victim selection process to favor ways that are less likely to cause conflicts during parallel accesses, proactively preventing conflicts rather than reacting to them.
Data Source
AI summary
An apparatus comprises a set associative cache, and cache replacement control circuitry to select, for a given set of the set associative cache, a victim cache entry to be replaced with a new cache entry. The victim cache entry is selected based on cache replacement selection values indicative of a relative priority for selection as the victim cache entry. In response to identifying a plurality of highest victim priority cache entries having equal cache replacement selection values indicative of equal highest priority to be selected as the victim cache entry, the cache replacement control circuitry is configured to select the victim cache entry based on a set-specific selection criterion which favours selection of a victim cache entry belonging to a preferred way for the given set, wherein the preferred way differs between at least two sets of the set associative cache.