Context-Indexed Cache Invalidation Filtering for Multi-Core CPUs
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Solution Overview
Problem
In systems with multiple CPU cores, invalidation requests for cache data can lead to performance issues due to the need to share and process these requests across all cores, causing inefficiencies and performance penalties, especially when one core repeatedly issues invalidations.
Innovation Solution
Implementing a data processing apparatus with cache circuitry indexed by execution contexts, receive circuitry for invalidation requests, invalidation circuitry, and filter circuitry to selectively invalidate data based on conditions, reducing unnecessary cache flushes by filtering irrelevant requests.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the entire cache is flushed in response to invalidation requests, then cache consistency is maintained, but cache performance deteriorates due to repeated full flushes
Solution Approach 1:
The patent segments the cache invalidation process by introducing execution context identifiers that divide the cache into context-specific regions. Instead of flushing the entire cache, only the relevant context-specific cache lines are invalidated. This segmentation allows the cache to maintain consistency for affected contexts while preserving data in other contexts, thereby maintaining cache performance.
Solution Approach 2:
The patent applies local quality by making the cache invalidation targeted rather than universal. Each cache line is associated with a specific execution context, allowing the system to apply invalidation locally to only those cache lines that need it, rather than flushing the entire cache. This localized approach maintains overall cache performance while ensuring consistency where required.
2Reliability
If cache checks are performed for each invalidation request, then cache consistency is ensured, but processing time increases
Solution Approach 1:
The patent implements preliminary action by pre-associating execution context identifiers with cache lines during cache population. This pre-tagging allows the invalidation logic to quickly identify relevant cache lines using the context identifier from the invalidation request, avoiding the need for exhaustive checks of all cache lines. The preliminary association of context identifiers enables fast targeted invalidation while maintaining consistency.
3Reliability
If invalidation requests are shared across all CPU cores, then system-wide cache consistency is maintained, but performance impact increases due to repeated invalidations from single cores
Solution Approach 1:
The patent segments the invalidation propagation mechanism by introducing execution context identifiers that allow each core to track which contexts it is affected by. Instead of broadcasting invalidations to all cores regardless of relevance, the system can filter invalidations based on context identifiers, reducing the burden on cores that are not affected by particular invalidation requests while maintaining system-wide consistency where needed.
Data Source
AI summary
A data processing apparatus is provided. Cache circuitry caches data, the data being indexed according to execution contexts of processing circuitry. Receive circuitry receives invalidation requests each referencing a specific execution context in the execution contexts. Invalidation circuitry invalidates at least some of the data in the cache circuitry and filter circuitry filters the invalidation requests based on at least one condition and, when the condition is met, causes the invalidation circuitry to invalidate the data in the cache circuitry.