Cache Line Eviction with Pending Control Request Tracking
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Solution Overview
Problem
In CXL (Compute Express Link) environments, managing the priority and order of cache line evictions with pending control requests is complex due to resource contention between external and internal requests, leading to potential out-of-order processing and blocked forward progress of external requests.
Innovation Solution
Implementing a counter mechanism in the cache set to track pending recalls, ensuring that internal requests are deferred when a cache way is evicted, and only processed once all pending recalls are completed, thereby maintaining in-order processing and ensuring forward progress of external requests.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If a cache line is evicted to process an external memory request, then the external request can proceed, but internal requests may be processed out-of-order or external requests may be blocked due to pending control requests
Solution Approach 1:
The patent applies preliminary action by checking whether a control request is pending before allowing cache line eviction. The memory device determines if a control request is outstanding and only permits eviction after the control request is complete, preventing out-of-order processing and ensuring external requests are not blocked.
2Speed
If internal requests are processed immediately upon cache line availability, then internal processing speed is improved, but external request forward progress may be blocked
Solution Approach 1:
The patent implements feedback by using a counter mechanism that tracks pending control requests. The counter is incremented when a control request is made and decremented when complete. This feedback loop ensures internal requests are deferred when external control requests are pending, maintaining external request forward progress while allowing internal processing when safe.
3Reliability
If a counter mechanism is added to track pending recalls, then request processing order is maintained, but hardware complexity increases
Solution Approach 1:
The patent applies universality by implementing a counter mechanism that serves multiple functions: tracking pending control requests, determining eviction eligibility, and managing request prioritization. This single counter structure handles multiple aspects of request management without requiring separate complex control logic for each function.
Data Source
AI summary
System and techniques for evicting a cache line with pending control request are described herein. A memory request—that includes an address corresponding to a set of cache lines—can be received. A determination can be made that a cache line of the set of cache lines will be evicted to process the memory request. Another determination can be made that a control request has been made to a host from the memory device and that the control request pending when it is determined that the cache line will be evicted. Here, a counter corresponding to the set of cache lines can be incremented (e.g., by one) to track the pending control request in face of eviction. Then, the cache line can be evicted.