L1 Cache Victim Reconfiguration for Single-Thread Miss Reduction

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Solution Overview

Problem

Current processor architectures face inefficiencies in single-thread mode due to limited cache memory, leading to increased cache misses and longer execution times, as they do not effectively utilize cache resources when switching from multi-threaded to single-threaded operations.

Innovation Solution

The system configures a second Level 1 (L1) data cache as a victim cache for the first L1 data cache in single-thread mode, effectively doubling the cache size and reducing cache misses by reconfiguring it in both write-through and copy-back modes, allowing data to be swapped between the L1 and victim caches without intermediate data transfers.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If a processor uses a fixed-size L1 data cache in single-thread mode, then the cache structure remains simple and fast, but the cache size is limited leading to frequent cache misses

Engineering Contradiction:

Improvecache hit rateVSAvoidcache structure

Core Design Contradiction:

ReliabilityVSDevice complexity

Solution Approach 1:

The cache system dynamically reconfigures between single-thread mode (using only L1 cache) and multi-thread mode (using L1 and L2 caches simultaneously). The mode selection logic monitors thread execution state and activates the appropriate cache configuration, allowing the system to adapt cache resources to current workload requirements without physical reconfiguration.

Inventive Principle:

Principle #15Dynamics

Solution Approach 2:

The L2 cache serves dual purposes: it functions as the secondary cache for multi-threaded workloads and as an expanded cache resource for single-threaded workloads. By enabling the L2 cache to be accessed in single-thread mode when needed, the system maximizes the utility of existing cache hardware without requiring additional cache memory resources.

Inventive Principle:

Principle #6Universality (Multi-functionality)

2Productivity

If the processor switches from multi-threaded to single-threaded operations, then execution focus improves, but cache resources are not effectively utilized leading to performance loss

Engineering Contradiction:

Improveexecution efficiencyVSAvoidcache performance

Core Design Contradiction:

ProductivityVSReliability

Solution Approach 1:

Inventive Principle:

Principle #15Dynamics

Solution Approach 2:

The system proactively detects when a thread is executing in single-thread mode and pre-configures the cache subsystem to utilize both L1 and L2 caches. This preliminary detection and configuration prevents cache performance degradation by ensuring the expanded cache structure is ready before cache misses occur during single-threaded execution.

Inventive Principle:

Principle #10Preliminary action

3Reliability

If the cache size is increased to reduce cache misses, then cache hit rate improves, but access time to cache memory increases

Engineering Contradiction:

Improvecache hit rateVSAvoidcache access time

Core Design Contradiction:

ReliabilityVSSpeed

Solution Approach 1:

The cache system is segmented into two distinct levels: L1 cache for fast, frequent accesses and L2 cache for larger capacity needs. The segmentation allows the system to maintain a small, fast L1 cache while providing access to a larger L2 cache when additional capacity is required, optimizing the trade-off between access speed and hit rate.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The system adds a temporal dimension to cache access by implementing a mode selection mechanism that determines whether to access L1 alone or both L1 and L2 caches based on the current execution mode. This dimensional approach allows the system to expand cache capacity on-demand without permanently increasing the critical path access time for all operations.

Inventive Principle:

Principle #17Another dimension (Dimensionality change)

4Loss of time

If the processor utilizes more cache memory in single-thread mode, then execution time decreases, but power consumption increases

Engineering Contradiction:

Improveexecution timeVSAvoidpower consumption

Core Design Contradiction:

Loss of timeVSUse of energy by moving object

Solution Approach 1:

Inventive Principle:

Principle #15Dynamics

Solution Approach 2:

The system changes the operational parameters of the cache subsystem based on execution mode. In single-thread mode, the L2 cache is activated and configured for use, expanding the effective cache capacity. In multi-thread mode, the system reverts to using only L1 cache for each thread, reducing power consumption. This parameter change approach allows flexible adaptation to workload requirements.

Inventive Principle:

Principle #35Parameter changes

Data Source

PatentUS9547593B2Systems and methods for reconfiguring cache memory

Publication Date: 2017.01.17 NXP USA INC

AI summary

A microprocessor system is disclosed that includes a first data cache that is shared by a first group of one or more program threads in a multi-thread mode and used by one program thread in a single-thread mode. A second data cache is shared by a second group of one or more program threads in the multi-thread mode and is used as a victim cache for the first data cache in the single-thread mode.