SLC Cache Migration Control for Consistent QLC Memory Writes
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Solution Overview
Problem
Existing memory sub-systems lack adequate control mechanisms for data transfer rates, leading to significant variance and unwanted latency, particularly in systems using Quad-Level Cell (QLC) memory, which affects host system performance.
Innovation Solution
Implementing a memory sub-system with single-level cell memory caching and a rate control manager that dynamically adjusts data transfer rates (H2C, C2D, C2C, D2D) based on free space and host bandwidth, using a gear-based approach and delayed completion entry returns to manage write commands.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If data transfer rates are not controlled in memory sub-systems, then data transfer flexibility is maintained, but significant variance and unwanted latency occur affecting host system performance
Solution Approach 1:
The patent implements dynamic rate control that adjusts data transfer rates between host system and cache band, and between cache band and data band, based on real-time conditions. The rate control manager dynamically modifies host-to-cache data rate and cache-to-data data rate to optimize performance and minimize latency while maintaining reliability.
Solution Approach 2:
The patent employs feedback mechanisms where the rate control manager continuously monitors data transfer operations and adjusts rates based on system state. Completion entries are used to provide feedback to the host system about write command status, enabling the system to adapt transfer rates to current conditions and reduce latency.
2Productivity
If high data transfer rates are used from host to cache, then productivity is improved, but cache free space depletes rapidly causing bottlenecks
Solution Approach 1:
The rate control manager dynamically adjusts the host-to-cache data rate based on available cache free space. When cache free space is sufficient, higher data rates are permitted to maximize productivity. When cache free space depletes, the rate is reduced to prevent bottlenecks and maintain steady data flow to the data band.
Solution Approach 2:
The system proactively manages cache free space by controlling the host-to-cache data rate before the cache becomes full. This preliminary control prevents cache overflow conditions and ensures continuous operation without bottlenecks.
3Quantity of substance
If aggressive data migration from cache to data band is implemented, then cache free space is maintained, but data band write performance degrades due to QLC memory constraints
Solution Approach 1:
The rate control manager dynamically controls the cache-to-data data rate based on data band availability and QLC memory constraints. Instead of aggressive migration, the system adjusts the rate to match data band write capabilities, maintaining cache free space while preserving data band write performance.
Solution Approach 2:
The system changes the data transfer rate parameter for cache-to-data operations to optimize overall performance. By adjusting this parameter based on QLC memory constraints, the system balances cache free space maintenance with data band write performance.
4Ease of operation
If completion entries are returned immediately to host system, then host system responsiveness is improved, but data transfer rate control precision is reduced
Solution Approach 1:
Completion entries are prepared in advance with timestamp information that encodes rate control data. This preliminary preparation allows the host system to receive responsive completion notices while the embedded timestamp provides precise rate control information for future operations.
Solution Approach 2:
Timestamp information in completion entries acts as an intermediary that carries rate control data to the host system. This intermediary mechanism provides both immediate responsiveness and precise rate control information without requiring separate control channels.
Data Source
AI summary
Processing logic in a memory sub-system detects an occurrence of a rate control trigger event in the memory sub-system, the memory sub-system comprising a memory device, and collects one or more operating statistics of the memory sub-system at a time of the rate control trigger event. The processing logic further determines, based on the one or more operating statistics, a target rate for migrating data from a cache of the memory device to a primary storage band of the memory device and configures one or more data rate control parameters of the memory sub-system based on the target rate for migrating data from the cache to the primary storage band of the memory device.