SSD Command Aging via Doorbell Timestamps
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing data storage systems face challenges in accurately accounting for the age of commands prior to entering the queue, leading to potential timeouts and degradation of quality of service due to commands aging in the storage device queue.
Innovation Solution
Implementing a system where multiple doorbell requests for the same command queue are used to save timestamps, allowing the storage device to accurately age commands by associating them with the timestamp of their arrival, and optionally using statistical values like average timestamps between first and last doorbell requests.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If commands are assigned timestamps at host receipt time, then quality of service accuracy is improved, but device complexity increases due to multiple timestamp registers and aging algorithms
Solution Approach 1:
The system records timestamps at the doorbell request stage (when the host notifies the storage device of new commands) rather than waiting until commands are actually fetched. This preliminary timestamp recording captures the true arrival time before the storage device's idle periods can cause additional delays, thereby accurately reflecting the host's perspective on command age without requiring complex post-fetch adjustments
Solution Approach 2:
The patent introduces doorbell request timestamps as an intermediary mechanism that bridges the host and storage device timing perspectives. The doorbell request serves as a mediator event that both parties can reference, allowing the storage device to assign commands timestamps based on when the host notified it of new work, rather than when the storage device actually processed the command queue
2Use of energy by moving object
If the storage device goes idle between receiving doorbell requests and fetching commands, then energy consumption is reduced, but command aging accuracy deteriorates causing timeouts
Solution Approach 1:
The system performs the critical timing action of recording the command arrival timestamp at the doorbell request stage, before the storage device enters idle mode. This ensures the timestamp captures the true arrival time even if the device subsequently goes idle for extended periods. The timestamp is preserved and applied when commands are eventually fetched, maintaining accuracy without requiring the device to remain active
Solution Approach 2:
The storage device uses its own doorbell request events to generate timestamps for command aging, rather than relying on host-provided timestamps or external time sources. This self-service approach allows the device to independently track command age based on when it was notified of new commands, ensuring consistency between host and device perspectives without additional complexity
Data Source
AI summary
A method and apparatus for providing accurate command aging in a data storage device. A host provides multiple doorbell requests for the same command queue and a timestamp is saved for each request. When the storage device fetches the commands associated with the requests, the commands are all given the value of the timestamp associated with the requests and placed into the command queue and the aging algorithm of the storage device ages the commands. In an alternate embodiment, the commands may be assigned timestamps based on statistical values such as an average value, between the first and last doorbell request timestamps.