Home Node Coherency Control for Exclusive Access Serialization
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Solution Overview
Problem
In data transfer protocols like the AMBA CHI protocol, ensuring data coherence and serialization across nodes in a system on chip (SoC) or network on chip (NoC) is challenging, particularly in preventing live-lock situations due to exclusive contention between nodes.
Innovation Solution
The implementation of a home node that serializes data access operations and controls coherence among data handling nodes, allowing requesting nodes to communicate for exclusive access and instruct other nodes to invalidate data instances when necessary, thereby preventing live-lock scenarios.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If multiple nodes simultaneously access data for exclusive operations, then system throughput increases, but live-lock situations occur due to exclusive contention
Solution Approach 1:
The patent applies preliminary action by having the home node detect whether a requesting node currently holds an instance of data before executing an exclusive store operation. This detection happens in advance of the actual store operation, allowing the system to prevent live-lock situations before they occur. The home node issues a detection request to the requesting node, and only proceeds with the exclusive store if the detection confirms the node still holds the data instance, thereby preventing contention-based deadlocks while maintaining throughput.
2Reliability
If the home node validates data coherence for every access, then data consistency is ensured, but access latency increases
Solution Approach 1:
The patent applies partial action by having the home node selectively validate data coherence only when necessary - specifically, before executing exclusive store operations. The home node detects whether the requesting node currently holds an instance of data, and only performs coherence validation and potential invalidation of other nodes' copies in this specific scenario. For other access types, the home node allows direct access without full validation, thereby reducing access latency while maintaining data consistency where required.
3Reliability
If the home node instructs other nodes to invalidate data copies, then coherence is maintained, but communication overhead increases
Solution Approach 1:
The patent applies preliminary anti-action by having the home node detect whether a requesting node holds data before executing an exclusive store operation. This preliminary detection prevents the need for subsequent invalidation communications in cases where the data is already held by the requesting node, thereby avoiding unnecessary communication overhead. The home node only instructs other nodes to invalidate their copies when the detection confirms the requesting node still holds the data, thus maintaining coherence control while minimizing redundant communications.
Data Source
AI summary
Circuitry comprises a set of two or more data handling nodes each having respective storage circuitry to hold data; and a home node to serialise data access operations and to control coherency amongst data held by the one or more data handling nodes so that data written to a memory address is consistent with data read from that memory address in response to a subsequent access request; in which: a requesting node of the set of data handling nodes is configured to communicate a request to the home node for exclusive access to a given instance of data at a given memory address; and the home node is configured, in response to the request, to communicate information to other data handling nodes of the set of data handling nodes to control handling, by those other data handling nodes, of any further instances of the data at the given memory address which are held by those other data handling nodes.