Castout Handling in Distributed Cache Topology
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Solution Overview
Problem
In distributed cache topologies, existing solutions require each remote cache to perform two directory lookups when a cache miss occurs: one to check if data is stored and another to determine if the cache can receive a castout, leading to inefficiencies in data access and processing.
Innovation Solution
A single bus transaction message is used to convey both the cache address for a cache miss and the cache line to be evicted, allowing remote caches to determine if they have a cache hit and can accept the castout using a shared index, thus reducing the number of directory lookups to one.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If existing solutions are used for castout handling in distributed cache topology, then remote caches can determine data storage status, but each remote cache must perform two directory lookups which reduces system performance
Solution Approach 1:
The patent combines two separate directory lookup operations into a single unified lookup operation. When a castout message is received, the remote cache performs one directory lookup using the castout tag to simultaneously determine both whether the data is stored in this cache and whether the cache can receive the castout, eliminating the need for two separate lookups and improving system performance
Solution Approach 2:
The patent makes the single directory lookup serve multiple functions: it determines data presence, evaluates castout acceptance capability, and provides information for both cache hit detection and castout handling. This multi-functional approach replaces the previous two separate lookup operations
2Loss of information
If two separate directory lookups are performed, then comprehensive cache status information is obtained, but the number of processing steps increases leading to higher latency
Solution Approach 1:
The patent merges the information gathering function of two separate lookups into a single lookup operation. By using the castout tag as the lookup key, the system simultaneously obtains data presence information and castout acceptance capability in one operation, reducing processing latency while maintaining information completeness
Solution Approach 2:
The patent performs the directory lookup using the castout tag beforehand, which provides all necessary information for both cache hit detection and castout acceptance evaluation in advance, eliminating the need for subsequent additional lookup operations
Data Source
AI summary
Castout handling in a distributed cache topology, including: detecting, by a first cache of a plurality of caches, a cache miss; providing, by the first cache to each other cache of the plurality of caches, a message comprising: data indicating a cache address corresponding to the cache miss; and data indicating a cache line to be evicted.