Cache Lookup Response Filtering for Parallel Invalidation

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Solution Overview

Problem

In data processing systems, there is a risk of conflicts between cache invalidation commands and ongoing cache lookup requests, leading to potential delays and performance issues due to the need to stall either cache invalidation or cache lookups.

Innovation Solution

The implementation of cache lookup response filtering circuitry that determines whether a hit-indicating cache lookup response conflicts with an in-progress cache invalidation command by comparing the invalidation scope information with the invalidation qualifying information from the cache entry, and treats conflicting responses as miss-indicating to avoid such conflicts.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Productivity

If cache invalidation commands are processed immediately without stalling, then productivity is improved, but reliability deteriorates due to potential conflicts with ongoing cache lookup requests

Engineering Contradiction:

Improvecache invalidation throughputVSAvoidcache response accuracy

Core Design Contradiction:

ProductivityVSReliability

Solution Approach 1:

The patent introduces an intermediary filtering mechanism that sits between the cache and the lookup requestor. This filter examines cache lookup responses to determine if they conflict with in-progress invalidation commands, and selectively blocks or modifies responses accordingly. This intermediary layer allows both cache invalidation and lookup operations to proceed in parallel while maintaining reliability by preventing conflicting responses from reaching the requester.

Inventive Principle:

Principle #24Intermediary (Mediator)

Solution Approach 2:

The system implements feedback by having the cache lookup response filtering circuitry continuously monitor the state of in-progress invalidation commands and use this information to make real-time decisions about which cache responses to allow or block. The filtering decision is based on feedback about the overlap between the cache entry being accessed and the invalidation scope, enabling dynamic conflict resolution without stalling either operation.

Inventive Principle:

Principle #23Feedback

2Reliability

If cache lookups are stalled during invalidation processes, then reliability is improved, but productivity deteriorates due to delayed cache access

Engineering Contradiction:

Improvecache response accuracyVSAvoidcache lookup throughput

Core Design Contradiction:

ReliabilityVSProductivity

Solution Approach 1:

The patent enables continuous operation of both cache invalidation and cache lookup operations by eliminating the need to stall either process. The filtering circuitry allows valid cache responses to pass through uninterrupted while only blocking conflicting responses, thus maintaining continuous productive action in both the invalidation and lookup pipelines simultaneously without mutual interference.

Inventive Principle:

Principle #20Continuity of useful action

Solution Approach 2:

The intermediary filtering mechanism enables both operations to proceed in parallel by resolving conflicts at the response stage rather than preventing operations from executing. This allows continuous productive action in both pipelines while maintaining reliability through selective response filtering.

Inventive Principle:

Principle #24Intermediary (Mediator)

3Reliability

If cache invalidation scope is expanded to cover more cache entries, then reliability is improved, but device complexity increases due to more extensive conflict detection requirements

Engineering Contradiction:

Improveinvalidation completenessVSAvoidfiltering circuitry complexity

Core Design Contradiction:

ReliabilityVSDevice complexity

Solution Approach 1:

The filtering circuitry implements local quality by examining only the specific cache entry being accessed and comparing it locally against the invalidation scope, rather than performing a global analysis of all cache entries. This localized approach allows the system to handle expanded invalidation scopes with manageable complexity, as each filtering decision is made independently based on local information about the specific cache line being accessed.

Inventive Principle:

Principle #3Local quality

Data Source

PatentUS12346253B2Cache lookup response filtering

Publication Date: 2025.07.01 ARM LTD

AI summary

Cache invalidation circuitry responds to a cache invalidation command specifying invalidation scope information indicative of at least one invalidation condition, to control a cache to perform an invalidation process to invalidate cache entries satisfying the invalidation condition(s). Cache lookup circuitry issues to the cache a cache lookup request specifying address information, to request that the cache returns a cache lookup response. Cache lookup response filtering circuitry is responsive to a given hit-indicating cache lookup response which provides cached information and invalidation qualifying information returned from a corresponding valid cache entry, to determine whether the given hit-indicating cache lookup response conflicts with an in-progress cache invalidation command, based on the invalidation scope information specified by the in-progress cache invalidation command and the invalidation qualifying information, and when conflict is detected, causes the given hit-indicating cache lookup response to be treated as a miss-indicating cache lookup response.