Victim Cache Allocation for Shared System Cache Thrashing
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Solution Overview
Problem
Computing systems face inefficiencies in handling data eviction due to cache thrashing, where data is repeatedly evicted from the shared system cache, leading to increased latency and power consumption as processors frequently access system memory.
Innovation Solution
Implementing a victim cache with a cache controller that allocates evicted data based on its usefulness, determined by factors such as miss requests, prefetch accuracy, and streaming hints, to store data that is likely to be accessed again, thereby reducing unnecessary evictions and cache thrashing.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the shared system cache size is increased to store more data, then data retrieval efficiency is improved, but the available on-chip area is exceeded and design constraints are violated
Solution Approach 1:
The victim cache is nested within the shared system cache structure, creating a hierarchical storage system where the victim cache serves as an additional layer for storing evicted data that may be reused, effectively increasing storage capacity without proportionally increasing the primary cache area
Solution Approach 2:
The solution adds a temporal dimension to cache storage by implementing a victim cache that retains evicted data for a period, transforming the cache from a simple replacement structure to a multi-layered temporal storage hierarchy that improves retrieval efficiency without expanding the primary cache area
2Reliability
If all evicted data is stored in the shared system cache, then data availability is improved, but cache thrashing occurs and processors frequently access system memory with larger latency
Solution Approach 1:
The allocator selectively assigns different qualities of storage to different data based on their usefulness metrics, storing only high-value evicted data in the victim cache while allowing low-value data to be quickly replaced, thereby reducing cache thrashing and improving access latency for frequently needed data
Solution Approach 2:
The system changes the parameter of data retention by introducing a usefulness threshold that determines whether evicted data should be retained in the victim cache or discarded, dynamically adjusting cache content based on predicted future utility rather than using a fixed retention policy
3Quantity of substance
If the victim cache stores all evicted data, then memory capacity is improved, but the allocator complexity increases due to multiple factors to evaluate
Solution Approach 1:
The allocator implements partial action by evaluating only the most critical usefulness factors rather than exhaustively analyzing all possible data characteristics, storing only the portion of evicted data that meets the usefulness threshold, thereby managing complexity while still improving cache capacity utilization
Data Source
AI summary
A system and method for efficiently handling data selected for eviction in a computing system. In various embodiments, a computing system includes one or more processors, a system memory, and a victim cache. The cache controller of a particular cache in a cache memory subsystem includes an allocator for determining whether to allocate data evicted from the particular cache into the victim cache. The data fetched into the first cache includes data fetched to service miss requests, which includes demand requests and prefetch requests. To determine whether to allocate, the allocator determines whether a usefulness of data fetched into the particular cache exceeds a threshold. If so, the evicted data is stored in the victim cache. If not, the evicted data bypasses the victim cache. Data determined to be accessed by a processor is deemed to be of a higher usefulness.