Address Translation Cache Retention for Selective Attribute Invalidation
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Solution Overview
Problem
Cached translation entries in data processing systems become incorrect when a page table entry attribute is modified, leading to cache misses and slower translation due to the necessity of invalidating all entries, even if not all modifications render them invalid.
Innovation Solution
A data processing apparatus that retains valid translation entries in the cache by modifying control information in response to specific attribute modifications in page table entries, allowing subsequent lookups to utilize these entries without unnecessary invalidation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If translation entries are invalidated in the cache when a page table entry attribute is modified, then correctness of translation is maintained, but translation speed deteriorates due to cache misses
Solution Approach 1:
The patent applies local quality by differentiating between various types of page table entry modifications. Instead of uniformly invalidating all translation entries when any attribute changes, the system selectively invalidates only those entries corresponding to modified attributes, while retaining entries for unchanged attributes. This localized approach maintains correctness for modified translations while preserving speed benefits for unchanged translations.
Solution Approach 2:
The patent implements partial action by performing invalidation only to the extent necessary. When a page table entry attribute is modified, the system invalidates only the specific translation entries that correspond to that modified attribute, rather than invalidating all translation entries in the cache. This partial invalidation strategy maintains reliability for affected translations while minimizing the performance penalty of cache misses.
2Stability of the object's composition
If all translation entries are invalidated upon attribute modification, then consistency is ensured, but translation efficiency deteriorates due to increased page table lookups
Solution Approach 1:
The system applies local quality by tracking which specific translation entries correspond to modified page table attributes and invalidating only those local entries. This selective approach maintains translation consistency for modified entries while preserving efficient cached translations for unchanged entries, thereby maintaining overall translation efficiency.
Solution Approach 2:
The patent implements partial invalidation action by invalidating only the subset of translation entries that correspond to modified page table attributes. This partial action ensures consistency where needed while avoiding unnecessary invalidations that would reduce translation efficiency, thus resolving the contradiction between consistency and productivity.
3Speed
If translation entries are retained in the cache after attribute modification, then translation speed is maintained, but incorrect translations may be used
Solution Approach 1:
The patent applies local quality by selectively retaining translation entries in the cache based on whether their corresponding page table attributes have been modified. Translation entries for unchanged attributes are retained to maintain speed, while entries for modified attributes are invalidated to ensure reliability. This localized differentiation resolves the contradiction between speed and accuracy.
4Stability of the object's composition
If control information is modified for each page table attribute change, then cache coherence is maintained, but cache performance deteriorates due to frequent modifications
Solution Approach 1:
The system applies local quality by modifying control information only for the specific translation entries whose corresponding page table attributes have changed. This selective modification approach maintains cache coherence for affected entries while minimizing unnecessary control information modifications, thus preserving overall cache performance.
Data Source
AI summary
An apparatus and method are provided for storing a plurality of translation entries in a cache, each translation entry corresponding to one of a plurality of page table entries and defining a translation between a first address and a second address, and encoding control information indicative of an attribute of each page table entry; returning, in response to a lookup querying a first lookup address, a corresponding second address when the first lookup address corresponds to one of the plurality of translation entries stored in the cache; modifying at least some of the control information in response to notification of a modification of the attribute in a page table entry; and retaining in the cache at least one translation entry corresponding to the page table entry for use in a subsequent address lookup querying a corresponding first lookup address in response to the notification of the modification of the attribute in the page table entry.