PCIe TLP Alignment Retry for SSD Transfer Efficiency
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Solution Overview
Problem
In data storage devices like solid state drives (SSDs), unaligned transactions can lead to transfer failures and performance loss due to misalignment with host DRAM lines, as the NVMe and PCIe protocols operate at different layers of the protocol stack, often resulting in suboptimal alignment and size configurations.
Innovation Solution
A data storage device with a controller that issues unaligned transactions, detects transfer failures, and retries them with alternative alignments or sizes, using a host address grouping table to store successful adjustments for future transactions within the same address range.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If data transfers are aligned to host DRAM line to optimize performance, then transfer efficiency is improved, but flexibility in handling different access patterns is reduced
Solution Approach 1:
The system dynamically adjusts alignment requirements based on the specific transaction type and host device capabilities. The controller can switch between aligned and unaligned transaction modes depending on the workload characteristics, allowing optimal performance for both sequential and random access patterns without being constrained to a fixed alignment regime
Solution Approach 2:
The patent changes the alignment parameter from a fixed requirement to a variable that can be adjusted based on transaction characteristics. By modifying alignment parameters dynamically, the system achieves high transfer efficiency for aligned transactions while maintaining the ability to handle unaligned transactions when needed for different access patterns
2Productivity
If maximum TLP size is used for data transfers, then data transfer throughput is improved, but compatibility with host devices having different alignment requirements is reduced
Solution Approach 1:
The controller dynamically selects TLP size based on host device capabilities and transaction requirements. Rather than being locked into a fixed maximum TLP size, the system can adaptively choose appropriate transfer sizes to maintain high throughput while ensuring compatibility with various host devices that may have different alignment and size preferences
Solution Approach 2:
The system changes the TLP size parameter from a fixed maximum value to a variable that can be adjusted per transaction. This allows the controller to optimize data transfer throughput by using larger TLP sizes when appropriate while maintaining compatibility with host devices that require smaller or differently-aligned transfers
3Adaptability or versatility
If unaligned transactions are issued to match host device access patterns, then adaptability to host requirements is improved, but transfer reliability is reduced due to misalignment with memory boundaries
Solution Approach 1:
The controller acts as an intermediary between the host device and the storage memory. It receives unaligned transaction requests from the host, translates and reissues them as properly aligned transactions to the memory device, and then manages the data reassembly. This intermediary function maintains transfer reliability while preserving adaptability to host access patterns
Solution Approach 2:
The system segments unaligned transactions into multiple aligned sub-transactions. By breaking down a single unaligned transaction request into several properly aligned segments that can be processed reliably by the memory device, the system maintains both adaptability to host requirements and transfer reliability through proper alignment
Data Source
AI summary
A data storage device includes a memory device and a controller coupled to the memory device. The controller is configured to issue an unaligned transaction, determine that there is a transfer failure indication for the unaligned transaction, and retry the unaligned transaction with either a different alignment or a different transfer size. The different alignment or the different transfer size is used for another unaligned transaction from a same address range upon successful retry of the unaligned transaction.