Lower-Level Cache XI Snapshot Tracking for Cache Coherence
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Current systems in symmetric multiprocessing (SMP) fail to perform absolute address comparisons between higher-level cache fetch controllers, leading to tunneling of stale data due to unprocessed cross-invalidate (XI) snapshots, which affects cache coherence and performance.
Innovation Solution
Implementing a lower-level cache management system with a fetch address table (FAT) and response sync states to monitor changes in shared caches, ensuring XI snapshots are processed before data is consumed, thereby reducing the need for redundant snapshots and maintaining cache coherence.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If current systems perform XI snapshots in SMP without absolute address comparisons, then cache operations proceed without complex validation, but stale data tunnels through and cache coherence is compromised
Solution Approach 1:
The patent introduces an intermediary mechanism (the response sync state and FAT-based tracking system) that mediates between cache operations and XI snapshot requirements. This intermediary tracks which addresses have been fetched and coordinates snapshot timing without requiring complex per-operation validation, thus maintaining coherence while managing complexity.
Solution Approach 2:
The system performs preliminary tracking of fetch operations through the FAT and response sync states before XI snapshots are needed. By pre-recorded address information and fetch status, the system prepares the necessary data structures in advance, allowing snapshots to be executed efficiently without retroactive complexity.
2Reliability
If XI snapshots are frequently taken to ensure coherence, then cache coherence is maintained, but performance penalties increase
Solution Approach 1:
Instead of continuously or frequently taking XI snapshots, the patent implements periodic snapshots triggered by specific conditions (address comparisons and response sync states). Snapshots are taken periodically when fetch operations indicate potential coherence issues, rather than on every cache operation, reducing overall snapshot frequency while maintaining coherence.
Solution Approach 2:
The system changes the parameter of snapshot timing from fixed/frequent to conditional/periodic based on fetch address tracking. By monitoring address parameters and response sync states, the system dynamically determines when snapshots are necessary, adjusting snapshot frequency based on actual coherence needs rather than applying a constant high frequency.
3Adaptability or versatility
If shared lower-level caches are implemented without response sync tracking, then cache sharing capability is enabled, but stale data propagation occurs
Solution Approach 1:
The patent implements a feedback mechanism through response sync states that track whether data has been fetched by other processors. This feedback information flows back to the cache system, allowing it to determine when stale data might propagate and when XI snapshots are needed, thus maintaining data freshness in shared cache environments.
Solution Approach 2:
The response sync state acts as an intermediary between the shared cache structure and the XI snapshot mechanism. It provides the necessary information about data freshness and fetch status without requiring direct complex interaction between cache sharing operations and snapshot management, enabling both cache sharing and data freshness maintenance.
Data Source
AI summary
A lower-level cache managing cross-core invalidation (XI) snapshots in a shared-memory multiprocessing system, wherein the management of XI snapshots reduces an amount of required snapshots while allowing shared lower-level caches, comprising: the lower-level cache maintaining respective response sync state for at least one processor in a plurality of processors signifying that a line may have been changed by another processor since last fetched by a requesting processor.