Speculative Directory Lookup for Coherence State Prediction
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing shared memory multiprocessing systems face challenges in coherence management, with hardware mechanisms being complex and costly to implement, while software approaches suffer from performance issues and inefficiencies in repeated coherence activities.
Innovation Solution
A multi-node computer system with a coherence directory and controller that predicts coherence states for coherence units, reducing the need for frequent coherence traps and improving performance by providing predicted coherence states based on previously accessed memory regions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If hardware coherence mechanisms are implemented, then coherence reliability is improved, but device complexity and implementation cost increase
Solution Approach 1:
The patent introduces a directory structure as an intermediary component that mediates coherence management between processors and memory. The directory tracks coherence states and provides speculative lookups, acting as a mediator that reduces the complexity of direct hardware coherence enforcement while maintaining reliability through structured state management.
Solution Approach 2:
The patent creates a speculative copy of the directory state to predict coherence outcomes before actual coherence operations occur. This copying mechanism allows the system to pre-determine coherence states, reducing the need for complex real-time hardware enforcement while maintaining correctness through verification against the actual directory state.
2Ease of repair
If software coherence mechanisms are used, then ease of repair and flexibility are improved, but performance and productivity deteriorate
Solution Approach 1:
The patent implements self-service through speculative directory lookups that automatically predict and prepare coherence states without requiring software intervention. The coherence controller autonomously performs directory reads, state predictions, and validation, eliminating the need for software coherence traps while maintaining the flexibility and repairability of software-based approaches.
Solution Approach 2:
The patent performs preliminary actions by conducting speculative directory lookups and predicting coherence states before actual coherence operations are needed. This advance preparation eliminates performance-critical software traps by pre-determining coherence outcomes, allowing the system to maintain software flexibility while achieving hardware-like performance.
3Reliability
If repeated coherence activity is performed, then data access completeness is improved, but coherence traffic and latency increase
Solution Approach 1:
The patent performs preliminary directory lookups and coherence state predictions before actual data access operations. By pre-determining coherence states for repeated access patterns, the system avoids redundant coherence traffic and latency while ensuring data access completeness through verification against the predicted states.
Solution Approach 2:
The patent implements feedback mechanisms where the coherence controller validates predicted coherence states against actual directory states and uses this information to refine future predictions. This feedback loop ensures data access completeness by correcting prediction errors while reducing latency through increasingly accurate speculative lookups for repeated operations.
Data Source
AI summary
In one embodiment, a node for a multi-node computer system comprises a coherence directory configured to store coherence states for coherence units in a local memory of the node and a coherence controller configured to receive a coherence request for a requested coherence unit. The requested coherence unit is included in a memory region that includes at least two coherence units, and the coherence controller is configured to read coherence states corresponding to two or more coherence units from the coherence directory responsive to the coherence request. The two or more coherence units are included in a previously-accessed memory region, and the coherence controller is configured to provide the requested coherence unit with a predicted coherence state responsive to the coherence states in the previously accessed memory region.