Shadow Submission Queue for Sequential Zone Writes
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Solution Overview
Problem
The sequential write required (SWR) zone model in zone storage architecture faces inefficiencies due to race conditions and errors in command ordering, leading to rejected commands and low adaptation rates in non-volatile memory express (NVMe) and universal flash storage (UFS) systems, as commands must be sequentially written to maintain performance.
Innovation Solution
Implementing a shadow submission queue (SQ) invisible to the host device and a temporary buffer to reorder commands on a per-zone or per-page basis, allowing out-of-order execution while ensuring sufficient storage is available for data and gaps, thereby enabling sequential writing.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If commands are sent in parallel to fill system pipelines, then productivity is improved, but command ordering reliability deteriorates due to race conditions and transfer errors
Solution Approach 1:
The patent introduces an intermediary buffer between the host submission queue and the execution queue. This buffer receives commands in parallel from the host, stores them temporarily, and releases them in sequential order to the execution queue, thereby maintaining both high pipeline utilization and correct command ordering
Solution Approach 2:
The patent implements preliminary action by pre-fetching and buffering commands in the intermediary buffer before they are executed. This allows the system to prepare multiple commands in advance while ensuring they are released in the correct sequential order, resolving the conflict between parallel input and sequential processing requirements
2Reliability
If out-of-order commands are rejected to maintain sequential writing, then command ordering reliability is preserved, but productivity decreases due to rejected commands and low adaptation rates
Solution Approach 1:
The intermediary buffer acts as a mediator that accepts out-of-order commands from the host without rejecting them. It temporarily stores these commands and releases them in sequential order to the execution queue, thereby maintaining sequential writing integrity while accepting all commands for processing
Solution Approach 2:
The patent changes the operational parameters of the buffer system by introducing an intermediary buffer with specific capacity and management policies. This allows the system to tolerate out-of-order arrivals while maintaining sequential execution, effectively changing how the system handles command ordering without rejecting valid commands
Data Source
AI summary
Commands can be placed in a shadow submission queue (SQ) that is invisible to a host device, and corresponding data can be placed in a temporary buffer. Upon executing any command, the shadow SQ is searched for any commands that can be executed. In so doing, sequential writing to a zone is possible for out of order fetched commands. To further increase granularity, the order can be on a per page basis within a zone such that commands can be taken out of order throughout the zone, but if a page can be filled, even if the page is out of order, the page can be written. In either the zone granularity or the page granularity situation, commands can be placed in the shadow SQ so long as there is sufficient storage available in the temporary buffer for both the data of the command and any gaps.