Hybrid Memory Controller Partitioning for Cache-Maintenance Latency
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Solution Overview
Problem
Existing memory systems face challenges in efficiently managing cache operations in hybrid memory systems, leading to increased latency and reduced speed performance due to interference between memory transactions and cache maintenance operations.
Innovation Solution
A hybrid memory system with a separate hybrid controller component that manages cache fetch and evict operations, utilizing a transaction-merging unit and control logic to identify available access slots in the memory transaction stream, allowing cache maintenance to be performed without interfering with execution unit requests.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If cache maintenance operations are performed in hybrid memory systems, then cache performance is improved, but memory transaction latency increases due to interference between cache operations and memory transactions
Solution Approach 1:
The system segments memory channels into dedicated cache maintenance channels and general-purpose memory channels. Cache maintenance operations are routed to specific channels that are separated from channels handling execution unit requests, allowing concurrent operation without interference and eliminating latency conflicts between cache sync and memory transactions.
Solution Approach 2:
A hybrid controller component acts as an intermediary between the memory controller and physical memory components. It receives requests from both the memory controller and cache, manages channel allocation, and coordinates traffic to prevent conflicts. The hybrid controller intelligently routes cache maintenance operations to available channels without blocking execution unit memory transactions.
2Device complexity
If a unified memory controller manages both memory transactions and cache operations, then device complexity is reduced, but performance degradation occurs due to resource contention
Solution Approach 1:
The controller functionality is segmented into a hybrid controller component that handles cache maintenance operations and a memory controller component that handles execution unit requests. This segmentation allows each component to optimize its operations independently, preventing resource contention while maintaining manageable system complexity through modular design.
Solution Approach 2:
The hybrid controller serves as an intermediary layer between the cache and physical memory, managing cache maintenance operations separately from the memory controller's management of execution unit transactions. This intermediary structure enables parallel processing of different memory operations without direct interference, preserving system performance.
3Device complexity
If cache sync operations are performed using existing memory channels, then device complexity is minimized, but read and write latency increases due to channel contention
Solution Approach 1:
Memory channels are segmented into dedicated cache maintenance channels and general-purpose channels for execution unit transactions. By assigning specific channels to cache sync operations, the system avoids contention with memory transactions while maintaining a relatively simple channel structure that doesn't require complete channel duplication.
Data Source
AI summary
A compute system includes an execution unit (e.g. of a CPU) with a memory controller providing access to a hybrid physical memory. The physical memory is “hybrid” in that it combines a cache of relatively fast, durable, and expensive memory (e.g. DRAM) with a larger amount of relatively slow, wear-sensitive, and inexpensive memory (e.g. flash). A hybrid controller component services memory commands from the memory controller component and additionally manages cache fetch and evict operations that keep the cache populated with instructions and data that have a high degree of locality of reference. The memory controller alerts the hybrid controller of available access slots to the cache so that the hybrid controller can use the available access slots for cache fetch and evict operations with minimal interference to the memory controller.