Cache Line Eviction via Sector Data Validation
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Solution Overview
Problem
Conventional memory sub-systems face data inconsistency issues when evicting cache lines, as invalid data is stored at the backing store alongside valid data, leading to performance degradation and inconsistencies.
Innovation Solution
The memory sub-system performs a read-modify-write operation to replace invalid data with valid data from the backing store or a secondary cache before evicting the cache line, ensuring that only valid data is stored at the backing store, thereby maintaining data consistency and improving performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If cache lines are evicted without checking for invalid data, then eviction speed is improved, but data consistency deteriorates
Solution Approach 1:
The system performs a preliminary check of the validity bit before eviction occurs. This advance detection allows the system to prepare for conditional eviction - only evicting cache lines marked as valid, thereby preventing invalid data from being written to the backing store while maintaining fast eviction processing.
Solution Approach 2:
The validity bit serves as feedback information that guides the eviction decision. By checking the validity bit status before eviction, the system receives feedback about whether the cache line should be evicted, ensuring data consistency is maintained without slowing down the eviction process.
2Quantity of substance
If invalid data is stored at the backing store alongside valid data, then cache capacity utilization is improved, but data consistency deteriorates
Solution Approach 1:
The system extracts the invalid data from the cache line by checking the validity bit and selectively evicting only the valid portions. This separation ensures that only valid data is written to the backing store, maintaining data consistency while still utilizing cache capacity effectively.
Solution Approach 2:
The validity bit provides local quality information about each cache line's data integrity. This allows differential treatment of cache lines during eviction - valid lines are evicted to the backing store, while invalid lines are handled differently, ensuring data consistency at the local level without affecting overall cache utilization.
3Reliability
If a read-modify-write operation is performed before eviction, then data consistency is improved, but operation time increases
Solution Approach 1:
The validity bit check is performed as a preliminary action before the full read-modify-write operation. This early validation determines whether the cache line should be evicted, avoiding unnecessary read-modify-write operations for invalid data and reducing overall eviction time while maintaining consistency.
Solution Approach 2:
Instead of always performing a full read-modify-write operation, the system applies partial action by first checking the validity bit. Only when the bit indicates valid data does the system proceed with the full read-modify-write operation, reducing unnecessary processing time while ensuring data consistency when needed.
Data Source
AI summary
An indication to perform an eviction operation on a cache line in a cache can be received. A determination can be made as to whether at least one sector of the cache line is associated with invalid data. In response to determining that at least one sector of the cache line is associated with invalid data, a read operation can be performed to retrieve valid data associated with the at least one sector. The at least one sector of the cache line that is associated with the invalid data can be modified based on the valid data. Furthermore, the eviction operation can be performed on the cache line with the modified at least one sector.