Snoop Filter Preserving Cache Replacement Data

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Solution Overview

Problem

In victim exclusive caches, replacement information is often lost during re-reference to the CPU, limiting the ability to preserve historical access data and efficiently manage cache replacement policies.

Innovation Solution

A snoop filter is used to store replacement information, allowing for the preservation of historical access data and intelligent replacement and aging of cachelines, with the snoop filter communicating replacement information between the victim exclusive cache and the master CPU during transactions, thereby maintaining and advancing existing replacement information.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Quantity of substance

If a victim exclusive cache is used to reduce memory traffic and improve cache efficiency, then cache storage efficiency is improved, but replacement information is lost during re-reference to the CPU

Engineering Contradiction:

Improvecache storage efficiencyVSAvoidreplacement information

Core Design Contradiction:

Quantity of substanceVSLoss of information

Solution Approach 1:

The patent introduces a snoop filter as an intermediary component between the victim exclusive cache and the master CPU. This snoop filter stores replacement information and metadata about cachelines, allowing the cache to maintain historical access data without polluting the main cache with redundant information. The snoop filter acts as a mediator that preserves replacement information during re-reference operations.

Inventive Principle:

Principle #24Intermediary (Mediator)

Solution Approach 2:

The patent segments the cache system into two distinct components: the victim exclusive cache for storing actual data and the snoop filter for storing replacement information and metadata. This segmentation allows each component to serve its specific function optimally without interfering with the other, preventing information loss while maintaining cache efficiency.

Inventive Principle:

Principle #1Segmentation

2Loss of information

If replacement information is stored in the snoop filter, then historical access data is preserved, but device complexity increases

Engineering Contradiction:

Improvehistorical access dataVSAvoidsystem structure

Core Design Contradiction:

Loss of informationVSDevice complexity

Solution Approach 1:

The snoop filter is designed to perform multiple functions: it stores replacement information, tracks coherency state of cachelines, filters memory requests, and manages replacement policies. By consolidating these functions into a single component, the patent reduces overall system complexity while preserving historical access data effectively.

Inventive Principle:

Principle #6Universality (Multi-functionality)

Data Source

PatentUS10360158B2Snoop filter with stored replacement information, method for same, and system including victim exclusive cache and snoop filter shared replacement policies

Publication Date: 2019.07.23 SAMSUNG ELECTRONICS CO LTD

AI summary

Embodiments of the present system and method provide cache replacement in a victim exclusive cache using a snoop filter where replacement information is not lost during a re-reference back to the CPU. Replacement information is stored in a snoop filter, meaning that historical access data may be fully preserved and allows for more flexibility in the LLC re-insertion points, without additional bits stored in a L2 cache. The present system and method further include snoop filter replacement technique. The present system and method passes replacement information between a snoop filter and a victim exclusive cache (e.g., LLC) when transactions move cachelines to and from a master CPU. This maintains and advances existing replacement information for a cacheline that is removed from the victim exclusive cache on a read, as well as intelligently replaces and ages cachelines in the snoop filter.