NoC Directory Structure with Encoded Value for Cache Coherency
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Solution Overview
Problem
In Network on Chip (NoC) systems, maintaining cache coherency while managing bandwidth and latency is challenging due to limitations in traditional interconnects and routing methods, leading to high latency and inefficient data retrieval from multiple agents.
Innovation Solution
A directory structure with an encoded value field is introduced to track the original holder of a data line, allowing for efficient identification and retrieval of potentially dirty agents, reducing unnecessary snoops and optimizing data delivery by directly providing dirty data from the agent with the most recent copy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If broadcast snoops are used to check all agents for data lines, then cache coherency is maintained, but bandwidth consumption increases and latency increases
Solution Approach 1:
The directory structure pre-stores the original holder information for each data line before any snooping operation is needed. When a data line is requested, the system already knows which agent originally held the data, allowing targeted snooping without needing to broadcast to all agents. This preliminary tracking action eliminates the need for exhaustive broadcast snoops while maintaining cache coherency.
Solution Approach 2:
The invention extracts and stores only the essential information (original holder identifier) from the complete agent state in the directory structure. This extracted information is sufficient to identify potentially dirty agents without requiring full state information to be transmitted or processed, reducing bandwidth consumption while maintaining the ability to ensure cache coherency.
2Reliability
If broadcast snoops are used to check all agents for data lines, then cache coherency is maintained, but latency increases
Solution Approach 1:
The directory structure pre-stores the original holder information for each data line before any snooping operation is needed. When a data line is requested, the system already knows which agent originally held the data, allowing targeted snooping without needing to broadcast to all agents. This preliminary tracking action eliminates the need for exhaustive broadcast snoops while maintaining cache coherency.
Solution Approach 2:
The directory structure acts as an intermediary that mediates between the data line request and the actual agent snooping operation. It provides the original holder information as an intermediate step, enabling the system to directly target the correct agent for snooping without iterating through all agents, thus reducing latency while ensuring coherency.
3Ease of manufacture
If traditional interconnects are used for NoC systems, then implementation is simpler, but scalability is limited and performance deteriorates
Solution Approach 1:
The invention segments the coherency management function by introducing a separate directory structure that independently tracks original holder information. This segmentation allows the NoC interconnect to maintain simplicity for basic data transmission while adding specialized coherency tracking capabilities that enable better performance and scalability without redesigning the entire interconnect architecture.
Data Source
AI summary
The present disclosure is directed to hardware hash tables, and more specifically, to generation of a cache coherent system such as in a Network on Chip (NoC). The present disclosure is further directed to a directory structure that includes a new field, referred to, for instance as, encoded value, which indicates the original owner of a dirty line. As an original holder may have held or modified the original line, by tracking the original holder, example implementations can track the agents that are potentially dirty, as the encoded value can indicate the agent with the most recently unique line, which can then be shared with the other agents.