Lower Level Cache Age Manipulation for Write-Back Reduction
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Solution Overview
Problem
Emerging storage class memories face challenges with slow write latency and high write frequency, which impact performance when used as DRAM replacements or in hybrid memory systems, necessitating control over the number of writes and write bandwidth.
Innovation Solution
A method and apparatus that determine whether a read request entering a lower level cache contains modified data, and if not, manipulate age information to reduce the number of write-backs to memory, distinguishing between clean and dirty cache lines to optimize eviction policies.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If storage class memory is used as DRAM replacement or in hybrid memory system, then read latency is improved, but write latency increases and write frequency becomes problematic
Solution Approach 1:
The system performs preliminary actions by manipulating age information of cache lines before write-back operations occur. By controlling the perceived age of clean cache lines, the system proactively prevents unnecessary write-backs to storage class memory, thereby avoiding the write latency penalty before it occurs.
Solution Approach 2:
The invention changes the parameter of cache line age information to control eviction behavior. By manipulating age metadata rather than physical cache contents, the system alters the timing characteristics of write-back operations, effectively reducing write latency without impacting read performance.
2Quantity of substance
If storage class memory is used in hybrid memory system, then memory capacity is improved, but write bandwidth requirements increase
Solution Approach 1:
The system extracts and identifies clean cache lines that are candidates for eviction, separating them from dirty cache lines that require write-back. By manipulating age information specifically for clean cache lines, the system removes unnecessary write operations from the memory subsystem, thereby reducing write bandwidth requirements while maintaining full memory capacity.
3Device complexity
If conventional cache eviction policies are used, then cache management is simplified, but number of write-backs to memory increases
Solution Approach 1:
The invention introduces age information manipulation as an intermediary mechanism between cache eviction policy and write-back operation. This intermediary layer allows the system to control write-back behavior without fundamentally changing the cache management structure, thereby reducing write-backs while maintaining relatively simple cache management.
Data Source
AI summary
A method and apparatus for reducing write-backs to memory is disclosed herein. The method includes determining whether a read/write request entering a lower level cache is a cache line containing modified data, and responsive to determining that the read/write request is not a cache line containing modified data, manipulating age information of the cache line to reduce a number of write-backs to memory.