Zero-Size L2 Cache Controller Logic for Memory Access
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Solution Overview
Problem
Computing systems face challenges in efficiently supporting a cache memory hierarchy, particularly when a zero-size cache is used in a level of the hierarchy, as it requires innovative mechanisms to manage memory access requests and data retrieval without storing data in non-existent caches, while maintaining system performance and reducing power consumption.
Innovation Solution
The implementation of a cache memory hierarchy with a level-one (L1) cache directly connected to the processor, a level-two (L2) cache controller that determines cacheability, and an option for level-three (L3) cache or system memory, where the L2 cache controller handles miss requests by retrieving data from L1 or lower-level memory, merging data for store operations, and preventing cache storage of non-cacheable data, ensuring efficient data transfer without relying on a physical L2 cache.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Area of stationary object
If an L2 cache is excluded from the computing system, then on-die area is reduced and power consumption is decreased, but the processor cannot support systems that require an L2 cache
Solution Approach 1:
The L2 cache controller is designed to perform multiple functions: it can operate as a traditional L2 cache controller when an L2 cache is present, and as a direct memory access controller when an L2 cache is absent. This multi-functionality allows the same hardware to support both configurations, resolving the contradiction between area reduction and adaptability.
Solution Approach 2:
The system dynamically adapts its behavior based on the presence or absence of an L2 cache. The L2 cache controller detects whether it is connected to an actual L2 cache or directly to memory and adjusts its operation accordingly. This dynamic behavior enables the processor to work with or without an L2 cache, maintaining versatility while allowing area optimization.
2Use of energy by moving object
If an L2 cache is excluded from the computing system, then power consumption is decreased, but memory access performance may be degraded
Solution Approach 1:
The L2 cache memory structure is extracted from the system, but the L2 cache controller functionality is retained. This allows the system to eliminate the power-hungry L2 cache memory while preserving the intelligent memory management capabilities of the controller, achieving power savings without severe performance degradation.
Solution Approach 2:
The L2 cache controller acts as an intermediary between the L1 cache and the L3 cache or system memory. It manages memory access requests, performs address translation, and coordinates data transfer, providing efficient memory access performance even without an L2 cache present in the hierarchy.
3Adaptability or versatility
If a zero size L2 cache is used, then the system can support both configurations, but the L2 cache controller must manage complex logic to determine cacheability and handle miss requests
Solution Approach 1:
The L2 cache controller performs preliminary actions by pre-fetching data and pre-managing address translation before actual memory access requests occur. It also pre-determines cacheability attributes and prepares miss request handling, reducing the complexity of real-time decision-making and streamlining the overall control logic.
Data Source
AI summary
A system and method for efficiently supporting a cache memory hierarchy potentially using a zero size cache in a level of the hierarchy. In various embodiments, logic in a lower-level cache controller or elsewhere receives a miss request from an upper-level cache controller. When the requested data is non-cacheable, the logic sends a snoop request with an address of the memory access operation to the upper-level cache controller to determine whether the requested data is in the upper-level data cache. When the snoop response indicates a miss or the requested data is cacheable, the logic retrieves the requested data from memory. When the snoop response indicates a hit, the logic retrieves the requested data from the upper-level cache. The logic completes servicing the memory access operation while preventing cache storage of the received requested data in a cache at a same level of the cache memory hierarchy as the logic.