Cache Entry Aging via Partition Identifier Matching
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Solution Overview
Problem
In multi-level cache systems, switching between virtual partitions leads to performance degradation due to the aging and removal of L2 cache entries from the L3 cache, resulting in the loss of relevant data and instructions, as the L3 cache contains little information for the prior partition when switched back, requiring retrieval from main memory.
Innovation Solution
A partition identifier is associated with each cache entry, and if it matches the previous partition identifier in a processor register, the entry is marked for slower aging, preventing premature removal from the L3 cache, thus maintaining relevant entries for longer periods.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If the L3 cache uses LRU algorithm to cast out addresses, then the cache management is simplified, but the L2 cache entries from previous partitions become stale and are removed, resulting in performance degradation when switching back to prior partitions
Solution Approach 1:
The patent applies local quality by differentiating the aging rate of cache entries based on their partition affiliation. Entries marked with the previous partition identifier receive a reduced aging rate, while other entries continue to age normally. This localized differentiation preserves relevant data for prior partitions without complicating the overall cache management system.
Solution Approach 2:
The patent introduces dynamic aging rates that can change based on entry characteristics. By making the aging rate dynamic rather than uniform, the system can adaptively preserve entries from previous partitions while maintaining efficient cache management. The aging rate becomes a variable parameter that responds to partition switching events.
2Productivity
If all L2 cache entries are cast out when switching virtual partitions, then the cache is optimized for the new partition, but the L3 cache contains very little information for the prior partition when switching back, requiring re-retrieval from main memory
Solution Approach 1:
The patent applies preliminary action by marking L2 cache entries with partition identifiers before they are cast out to the L3 cache. This advance identification allows the system to later recognize which entries belong to previous partitions and apply reduced aging rates, ensuring they remain available when needed without requiring re-retrieval from main memory.
Solution Approach 2:
The patent uses the partition identifier as an intermediary mechanism to track and manage cache entries across partition switches. This intermediary data structure enables the system to distinguish between entries from different partitions and apply appropriate aging strategies, thereby preserving useful information while optimizing for current partition workload.
3Device complexity
If the L3 cache acts as a victim cache for evicted L2 entries, then the cache hierarchy is simplified, but the aging process causes L2 entries to become stale quickly and be cast out, degrading performance during partition switches
Solution Approach 1:
The patent applies local quality by differentiating the aging rate of cache entries based on their partition affiliation. Entries marked with the previous partition identifier receive a reduced aging rate, while other entries continue to age normally. This localized differentiation preserves relevant data for prior partitions without complicating the overall cache management system.
Data Source
AI summary
A computer implemented method, apparatus, and computer usable code for managing cache data. A partition identifier is associated with a cache entry in a cache, wherein the partition identifier identifies a last partition accessing the cache entry. The partition identifier associated with the cache entry is compared with a previous partition identifier located in a processor register in response to the cache entry being moved into a lower level cache relative to the cache. The cache entry is marked if the partition identifier associated with the cache entry matches the previous partition identifier located in the processor register to form a marked cache entry, wherein the marked cache entry is aged at a slower rate relative to an unmarked cache entry.