Microprocessor Macro-Op Cache Invalidation for Fetch-Block Aborts

Resolve Bottlenecks,
Find Innovative SolutionsGenerate Solutions

Solution Overview

Problem

Conventional microprocessor cache systems face inefficiencies in micro-op caching due to fragmentation, conflict misses, and power consumption issues, particularly in high-performance superscalar designs, leading to increased latency and power consumption.

Innovation Solution

Implementing a macro-op cache with single-fetch and multi-fetch block entries, utilizing a prediction unit to optimize cache usage by predicting program instruction streams and building multi-fetch block entries from highly consistent sequences, thereby reducing fragmentation and power consumption.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Speed

If a conventional micro-op cache is used to store decoded micro-operations, then instruction execution speed is improved, but cache fragmentation and conflict misses increase leading to reduced cache hit rates

Engineering Contradiction:

Improveinstruction execution speedVSAvoidcache hit rate

Core Design Contradiction:

SpeedVSReliability

Solution Approach 1:

The patent segments the cache into separate single-fetch block entries and multi-fetch block entries. This segmentation allows different types of instruction blocks to be stored in optimized locations, reducing conflict misses and improving cache hit rates while maintaining fast instruction execution.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The patent introduces a new dimension to cache organization by implementing multi-fetch block entries that can speculatively store micro-operations for multiple future instruction blocks. This extends the cache's temporal coverage beyond single blocks, reducing fragmentation and improving hit rates without sacrificing execution speed.

Inventive Principle:

Principle #17Another dimension (Dimensionality change)

2Reliability

If the cache size is increased to reduce fragmentation and improve hit rates, then cache hit rate is improved, but power consumption and area increase

Engineering Contradiction:

Improvecache hit rateVSAvoidpower consumption

Core Design Contradiction:

ReliabilityVSUse of energy by stationary object

Solution Approach 1:

The patent uses partial action by implementing multi-fetch block entries that speculatively pre-fetch micro-operations for future instruction blocks. This allows the cache to serve multiple blocks without proportionally increasing its base size, improving hit rates while controlling power consumption through selective speculation.

Inventive Principle:

Principle #16Partial or excessive action

Solution Approach 2:

The patent applies preliminary action through speculative pre-fetching of micro-operations into multi-fetch block entries before they are actually needed. This prepares the cache in advance, improving hit rates without requiring a proportionally larger cache structure, thus controlling power consumption.

Inventive Principle:

Principle #10Preliminary action

3Productivity

If a prediction unit is added to build multi-fetch block entries speculatively, then cache hit rate and performance are improved, but device complexity increases

Engineering Contradiction:

ImproveperformanceVSAvoiddevice complexity

Core Design Contradiction:

ProductivityVSDevice complexity

Solution Approach 1:

The prediction unit operates autonomously to identify instruction block sequences and build multi-fetch block entries without requiring complex external control logic. This self-service approach improves performance through speculative pre-fetching while minimizing the increase in device complexity by using simple prediction heuristics.

Inventive Principle:

Principle #25Self-service

4Reliability

If multi-fetch block entries are used to reduce fragmentation, then cache hit rate is improved, but invalidation complexity increases when aborts occur

Engineering Contradiction:

Improvecache hit rateVSAvoidinvalidation complexity

Core Design Contradiction:

ReliabilityVSDevice complexity

Solution Approach 1:

The patent extracts and isolates the invalidation logic for multi-fetch block entries into a dedicated invalidation unit. This unit selectively invalidates only the affected portions of multi-fetch entries when aborts occur, reducing invalidation complexity compared to invalidating entire cache structures while maintaining high cache hit rates.

Inventive Principle:

Principle #2Taking out (Extraction)

Data Source

PatentUS12450067B1Microprocessor that performs selective multi-fetch block macro-op cache entry invalidation

Publication Date: 2025.10.21 VENTANA MICRO SYSTEMS INC

AI summary

A microprocessor includes a prediction unit (PRU) that predicts a sequence of fetch blocks (FBlks) in a program instruction stream and a macro-op (MOP) cache (MOC) that comprises MOC entries (MEs). An ME holds MOPs into which architectural instructions of one or more FBlks are decoded. The PRU receives a detection of a first instance in which execution of an ME caused a need for an abort and in response resets a counter of the ME. Subsequently, the PRU increments the counter when the PRU predicts the ME is present, invalidates the ME in response to detecting a predetermined number of instances in which execution of the ME caused a need for an abort before the counter reaches a threshold, and retains the ME in the MOC if the counter reaches the threshold before detecting the predetermined number of instances in which the ME caused a need for an abort.