Cache Partitioning for FIFO Data Retention
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Solution Overview
Problem
Data processing systems face inefficiencies in handling First-In-First-Out (FIFO) data traffic due to least recently used (LRU) cache management policies, which can lead to data eviction before it is read by the consumer, resulting in reduced cache hits and increased memory access, especially when the cache is undersized.
Innovation Solution
Implementing a caching agent with a FIFO traffic retention (FTR) policy that ages cache ways containing direct-to-cache (DTC) data and retains it until read or until a predetermined maximum age, allowing old data to be read after a longer latency, and using separate partitions with different caching algorithms for FIFO and temporal reuse traffic.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If LRU or PLRU cache management policies are used, then recently used data is kept in cache, but FIFO data is evicted before being read by the consumer
Solution Approach 1:
The cache is divided into multiple partitions, with at least one partition specifically designated for FIFO traffic. This segmentation allows the system to apply different cache management policies to different types of traffic, ensuring that FIFO data receives specialized handling while other data can use traditional LRU/PLRU policies.
Solution Approach 2:
The cache management system dynamically adapts its behavior based on traffic type. By detecting whether incoming data follows FIFO patterns or temporal reuse patterns, the system can apply appropriate retention policies - maintaining FIFO data until consumed while allowing LRU/PLRU policies for other traffic types.
2Quantity of substance
If cache size is reduced to meet capacity constraints, then cache memory is saved, but data is evicted before being read
Solution Approach 1:
Different regions or partitions of the cache have different qualities and retention characteristics. The FIFO-specific partition provides enhanced data retention guarantees for FIFO traffic, while other partitions can be optimized for different access patterns. This allows the system to maintain high cache hit rates for FIFO data even when overall cache size is limited.
3Productivity
If DTC IO is implemented, then memory access cost is reduced, but FIFO data is overwritten before reading
Solution Approach 1:
The system performs preliminary actions by pre-establishing FIFO-specific cache partitions with guaranteed retention policies before FIFO data arrives. This preliminary configuration ensures that when DTC IO writes FIFO data to cache, the data is protected from eviction until the consumer reads it, preventing information loss while maintaining high IO performance.
Data Source
AI summary
A processor package comprises a caching agent that is operable to respond to a first sequence of direct-to-cache (DTC) write misses to a partition in a set in a cache by writing data from those write misses to the partition. When the partition comprises W ways, the caching agent is operable to write data from those write misses to all W ways in the partition. After writing data from those write misses to the partition, and before any data from the partition in the set has been read, the caching agent is operable to receive a second sequence of DTC write misses to the partition, and in response, complete those write misses while retaining the data from the first sequence in at least W-1 of the ways in the partition. Other embodiments are described and claimed.