Cache Coherent Interconnect Entry-Exit Messaging for Agent Synchronization
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Solution Overview
Problem
In complex systems with asynchronous elements or elements without a memory cache, maintaining synchronization across clock boundaries in cache coherent interconnects becomes inefficient, leading to reduced network bandwidth and increased power consumption, especially when agents dynamically enter or exit the network.
Innovation Solution
Implementing a cache coherent interconnect with message builders and receivers as additional hardware blocks in network interface units (NIUs) to communicate entry/exit intentions using a transport interconnect, eliminating the need for dedicated wires and allowing flexible communication channels.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If dedicated wires are used to connect agents to the directory for entry/exit communication, then reliability of agent status tracking is improved, but device complexity and routing difficulty increase significantly
Solution Approach 1:
The patent introduces message builders and message receivers as intermediary components within the NIU. The message builder generates standardized exit messages when an agent leaves the cache coherent domain, and message receivers deliver these messages through the transport interconnect to the directory and other agents. This intermediary mechanism replaces complex dedicated wiring with a simplified message-passing architecture, reducing routing complexity while maintaining reliable agent status tracking.
2Reliability
If conventional synchronization protocols are used for asynchronous agents, then synchronization reliability is improved, but power consumption and network bandwidth usage increase
Solution Approach 1:
The patent implements partial synchronization by using exit messages that selectively inform only the directory and relevant agents about an agent's departure from the cache coherent domain. Instead of continuously synchronizing all agents with all other agents (excessive action), the system performs synchronization only when necessary (partial action) - specifically when an agent enters or exits the domain. This reduces power consumption and network bandwidth usage while maintaining synchronization reliability.
3Ease of operation
If simple wires connect agents to directory for dynamic transition, then ease of operation is improved, but system reliability deteriorates due to silent evictions and infinite loops
Solution Approach 1:
The patent implements a feedback mechanism where the directory sends acknowledgment messages back to the exiting agent to confirm that the exit message has been received and processed. This feedback loop ensures that the agent's departure is properly registered in the system, preventing silent evictions where an agent leaves without proper notification. The acknowledgment feedback also prevents infinite loops by confirming that the exit sequence has completed successfully, thereby maintaining network stability while preserving ease of operation for dynamic transitions.
Data Source
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AI summary
A cache coherent interconnect connected to one or more agents, using Network Interface Units (NIUs), and also having one or more internal modules, such as a directory, is provided with one or more message builders and message receivers. These message builders and message receivers are provided as additional hardware IP blocks incorporated into the various NIUs and modules. When an agent signals an intention to enter/exit the cache coherent interconnect, a message communicating this information is generated using message builders, and transmitted using the interconnect wiring as a "virtual wire" to one or more message receivers associated with directories that need to be aware of the entry/exit transition of the agent. The directories are provided with tracking engines to manage the entry/exit information and status of the agent. Interconnects may include a broadcast engine to provide distribution to, and aggregate acknowledgements from, a single source to multiple destinations.