Cache Hierarchy Eviction Control Circuitry
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Solution Overview
Problem
Existing cache hierarchy management techniques face challenges in increasing effective cache capacity without introducing complex control circuitry, particularly when operating with exclusive cache arrangements.
Innovation Solution
Implementing a most recently read eviction policy in association with chosen levels of cache, combined with prefetch circuitry, to selectively evict recently accessed content, thereby optimizing cache allocation and reducing the need for complex management techniques.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If caches operate in a fully exclusive arrangement to increase effective cache capacity, then the amount of content that can be retained within the cache hierarchy increases, but the complexity of the control circuitry required to maintain the exclusive arrangement increases significantly
Solution Approach 1:
The patent inverts the traditional LRU eviction approach by implementing a Most Recently Read (MRV) eviction policy. Instead of evicting least recently used content, the system evicts most recently read content from lower cache levels, which has been determined to be less valuable for retention. This inversion allows the system to achieve exclusive cache behavior benefits without requiring complex control circuitry to coordinate between cache levels, as the eviction decisions are made locally at each cache level based on simple read history tracking.
2Speed
If caches closer to processing circuitry are made smaller to enable faster access, then access speed improves, but the capacity of these caches is reduced
Solution Approach 1:
The patent extends the cache hierarchy into an additional dimension by implementing multi-level caching with MRV eviction. Instead of simply increasing the capacity of L1 cache (one-dimensional solution), the system creates a hierarchical structure with L1, L2, and potentially L3 caches, where each level serves different capacity and speed requirements. The MRV eviction policy enables efficient coordination between these levels, allowing smaller L1 cache to maintain fast access while the extended hierarchy provides increased effective capacity through intelligent content retention at lower levels.
Data Source
AI summary
An apparatus and method are provided for managing a cache hierarchy. The apparatus has processing circuitry for executing instructions, and a cache hierarchy for storing content for access by the processing circuitry when executing those instructions. The cache hierarchy has a plurality of levels of cache including a highest level of cache that is accessed prior to the other levels of cache in response to a request from the processing circuitry. Eviction control circuitry is provided in association with each level of cache, and the eviction control circuitry associated with a chosen level of cache in arranged to implement a most recently read eviction policy that causes content most recently read from the chosen level of cache to be selected for eviction from that chosen level of cache. It has been found that such an approach can significantly increase the effective cache capacity within the cache hierarchy, without the complexities often associated with other schemes.