Coherent Interconnect Snoop Filter Write Latency
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Solution Overview
Problem
Cache coherence issues in shared memory systems lead to increased latency during write operations due to the need for ensuring consistency between local caches, which can be inefficient with existing solutions.
Innovation Solution
A coherent interconnect system incorporating a snoop filter and a coherence manager that generates a snoop filter request and transmits write requests to a memory controller without waiting for a snoop filter response, allowing for immediate data updates and managing cache coherence through invalidation signals and strobe bit handling.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the system waits for snoop filter response before transmitting write requests to memory controller, then cache coherence is ensured, but write operation latency increases
Solution Approach 1:
The coherence manager transmits the write request and write data to the memory controller in advance, before receiving the snoop filter response. This preliminary action allows the write operation to proceed without waiting for the cache coherence check to complete, thereby reducing latency while maintaining coherence through subsequent invalidation signals.
Solution Approach 2:
The coherence manager acts as an intermediary that decouples the write request transmission from the snoop filter operation. It can send write requests to the memory controller independently while simultaneously managing snoop filter operations and cache invalidation, allowing parallel execution of coherence management and data writing.
2Reliability
If the system performs cache coherence operations by writing to shared memory, then consistency between local caches is maintained, but write operation speed decreases
Solution Approach 1:
The system performs preliminary transmission of write data to the memory controller before completing cache coherence validation. This allows the write operation to initiate immediately rather than waiting for coherence checks, improving write speed while maintaining consistency through follow-up invalidation signals to affected caches.
Solution Approach 2:
The coherence manager maintains continuous operation by allowing write requests to proceed to the memory controller without interruption from snoop filter operations. The cache coherence management continues in parallel through invalidation signals, ensuring both speed and consistency without sequential blocking.
Data Source
AI summary
A coherent interconnect is provided. The coherent interconnect includes a snoop filter and a circuit that receives a write request, strobe bits, and write data from a central processing unit (CPU); generates a snoop filter request based on the write request; and transmits, at substantially the same time, the snoop filter request to the snoop filter and the write request, the strobe bits, and the write data to a memory controller.