Trace Cache Coherency via Selective Entry Invalidation

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Solution Overview

Problem

Conventional microprocessor trace cache management is inefficient in terms of power and performance due to the need for invalidating entire trace cache entries upon modifications, which can occur frequently with self-modifying code events, leading to unnecessary power consumption and reduced performance.

Innovation Solution

A method and system for maintaining memory coherence in a trace cache by selectively invalidating trace cache entries based on detected modifications, using a maskable tag Content Addressable Memory (CAM) to compare addresses and masks, ensuring that only affected entries are invalidated, thereby minimizing power consumption and maintaining performance.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If entire trace cache entries are invalidated upon modifications, then memory coherency is maintained, but power consumption increases and performance deteriorates

Engineering Contradiction:

Improvememory coherencyVSAvoidpower consumption

Core Design Contradiction:

ReliabilityVSUse of energy by moving object

Solution Approach 1:

The trace cache is segmented into individual entries, each with its own validity tracking mechanism. Instead of invalidating the entire cache when a modification is detected, only the specific entries that correspond to modified cache lines are invalidated. This is achieved by dividing the cache into entries that can be independently managed and invalidated based on their specific modification status.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

Different parts of the trace cache have different validity states. Each entry is tracked individually to determine whether it needs invalidation. The system applies local invalidation only to entries that correspond to modified cache lines, while other entries remain valid and continue to be used. This localized approach maintains coherency where needed without unnecessarily invalidating the entire cache.

Inventive Principle:

Principle #3Local quality

2Reliability

If entire trace cache entries are invalidated upon modifications, then memory coherency is maintained, but processing performance decreases

Engineering Contradiction:

Improvememory coherencyVSAvoidprocessing performance

Core Design Contradiction:

ReliabilityVSProductivity

Solution Approach 1:

The trace cache is segmented into individual entries that can be independently invalidated. This segmentation allows the system to maintain coherency by invalidating only specific entries rather than the entire cache, thereby preserving valid entries and maintaining processing performance.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

Instead of performing the excessive action of invalidating the entire trace cache, the system applies partial invalidation only to the specific entries that correspond to modified cache lines. This partial action is sufficient to maintain coherency while avoiding the performance penalty of full cache invalidation.

Inventive Principle:

Principle #16Partial or excessive action

3Use of energy by moving object

If selective invalidation of trace cache entries is implemented, then power consumption is reduced, but device complexity increases

Engineering Contradiction:

Improvepower consumptionVSAvoidcache management complexity

Core Design Contradiction:

Use of energy by moving objectVSDevice complexity

Solution Approach 1:

The system performs preliminary actions by pre-establishing validity tracking mechanisms for each cache line and entry. Modification status is tracked in advance through cache line validity bits and entry-level validity flags, so that when invalidation is needed, the system can quickly identify and invalidate only the affected entries without complex real-time analysis.

Inventive Principle:

Principle #10Preliminary action

Solution Approach 2:

Intermediary structures such as validity bits associated with cache lines and validity flags associated with entries serve as mediators between the modification detection mechanism and the invalidation process. These intermediaries simplify the complexity by providing clear, pre-organized validity information that guides the invalidation process.

Inventive Principle:

Principle #24Intermediary (Mediator)

4Productivity

If selective invalidation of trace cache entries is implemented, then processing efficiency is improved, but measurement and detection complexity increases

Engineering Contradiction:

Improveprocessing efficiencyVSAvoidmodification detection complexity

Core Design Contradiction:

ProductivityVSDifficulty of detecting and measuring

Solution Approach 1:

Inventive Principle:

Principle #10Preliminary action

Data Source

PatentUS7747822B1Maintaining memory coherency with a trace cache

Publication Date: 2010.06.29 SUN MICROSYSTEMS INC

AI summary

A method and system for maintaining memory coherence in a trace cache is disclosed. The method and system comprises monitoring a plurality of entries in a trace cache. The method and system includes selectively invalidating at least one trace cache entry based upon detection of a modification of the at least one trace cache entry.If modifications are detected, then corresponding trace cache entries are selectively invalidated (rather than invalidating the entire trace cache). Thus trace cache coherency is maintained with respect to memory in a performance and power-efficient manner. The monitoring further accounts for situations where more than one trace cache entry is dependent on a single cache line, such that modifications to the single cache line result in invalidations of a plurality of trace cache entries.