Caching Bridge Architecture Preventing Snoop Conflicts
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Solution Overview
Problem
Prior art multi-core processors and computer systems face cache access conflicts due to the limitations of inclusive cache structures, such as last level caches (LLCs), which increase as the number of processor cores or agents grows, leading to performance degradation.
Innovation Solution
The implementation of a caching bridge architecture with cache bridge scheduling and ordering (CBSO) logic that manages and prevents conflicts by using internal and external request queues to handle cache accesses, including speculative snoop blocking mechanisms to prevent conflicts between external agent snoops and cross-snoops within a multi-core processor system.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If an inclusive cache structure (LLC) is used to service cache requests from multiple agents, then cache access conflicts are reduced, but snoop conflicts between external agents and cross-snoops increase as the number of cores increases
Solution Approach 1:
A snoop blocking mechanism is introduced as an intermediary between external agents and the LLC. This mechanism intercepts and blocks external snoop requests during critical periods when cross-snoops are in progress, preventing conflicts without requiring changes to the core cache architecture or snoop logic
Solution Approach 2:
The system performs preliminary detection of cross-snoop conditions before external snoops can occur. By detecting when a cross-snoop is in progress and proactively blocking external snoop requests in advance, the system prevents conflicts before they can arise, rather than resolving them after occurrence
2Adaptability or versatility
If the number of processor cores or agents is increased, then system capability is improved, but the number of potential snoop conflicts increases
Solution Approach 1:
The snoop management function is segmented into separate handling paths for external agents and cross-core requests. The snoop blocking mechanism creates a distinct control path that independently manages external snoop requests, separating them from the internal cross-snoop operations. This segmentation allows the system to scale to more cores without proportionally increasing conflict complexity
3Device complexity
If cache conflicts are allowed to occur, then system simplicity is maintained, but processor performance degrades due to multiple processing cycles required for conflict resolution
Solution Approach 1:
The snoop blocking mechanism acts as an intermediary that prevents conflicts before they degrade performance. By blocking external snoops during cross-snoop operations, the system eliminates the need for complex conflict resolution processing cycles, maintaining simple cache management logic while preserving processor performance
Data Source
AI summary
In various embodiments, hardware, software and firmware or combinations thereof may be used to prevent cache conflicts within microprocessors and/or computer systems. More particularly, embodiments of the invention relate to a technique to prevent cache conflicts within a processor and/or computer system in which a number of accesses may be made to a particular cache or group of caches.