Memory Command Queue Timing for Out-of-Order Sequence Recovery
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Solution Overview
Problem
Conventional memory systems face inefficiencies and potential deadlocks due to out-of-order command delivery from host systems, leading to performance degradation and throughput limitations, as they either reduce command queue depth or reorder commands, which can cause further delays and deadlocks.
Innovation Solution
Implementing a timer-based management system for command queues that maintains a fixed depth and stores out-of-order commands in a pending state, using a timeout policy to ensure missing commands are resent, thereby preventing deadlocks and optimizing command processing efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the command queue depth is reduced to handle out-of-order commands, then deadlock prevention is improved, but system throughput and productivity deteriorate
Solution Approach 1:
The command queue depth is made dynamic rather than fixed. The system adjusts the effective queue depth based on the detection of out-of-order commands, allowing the queue to expand when commands are in order and contract when out-of-order commands are detected, thus balancing deadlock prevention with throughput optimization
Solution Approach 2:
The system implements feedback mechanisms to detect out-of-order commands and adjust queue management accordingly. When out-of-order commands are detected, the system responds by modifying queue depth or command acceptance behavior, creating a closed-loop control system that adapts to maintain both reliability and productivity
2Manufacturing precision
If commands are reordered to maintain sequence, then command processing correctness is improved, but processing delays and deadlocks increase
Solution Approach 1:
The system performs preliminary detection of out-of-order commands before they cause processing delays or deadlocks. By detecting sequence violations early in the queue management process, the system can take preventive actions such as adjusting queue depth or notifying the host, avoiding the need for time-consuming reordering operations
Solution Approach 2:
The system introduces an intermediary mechanism (such as a sequence tracker or buffer management layer) between the host and the command execution engine. This intermediary detects out-of-order commands and manages the queue depth dynamically, allowing the system to maintain correctness without direct reordering of commands, thus reducing processing delays
3Productivity
If the command queue depth is increased to improve throughput, then productivity is improved, but the system becomes more susceptible to deadlocks from out-of-order commands
Solution Approach 1:
The command queue depth is made dynamic rather than fixed. The system adjusts the effective queue depth based on the detection of out-of-order commands, allowing the queue to expand when commands are in order and contract when out-of-order commands are detected, thus balancing deadlock prevention with throughput optimization
Solution Approach 2:
The system changes the parameter of queue depth dynamically based on command sequence analysis. When out-of-order commands are detected, the queue depth parameter is adjusted to prevent deadlocks, while maintaining higher depth values during periods of ordered command arrival to maximize throughput
Data Source
AI summary
Various embodiments described herein provide for handling out-of-order commands by managing a command queue of a memory system based on a timer. In particular, various embodiments stores an out-of-order command in a command queue of a memory system with a pending state that prevents its execution and removal until a missing command preceding (the select command in the sequence of commands) is received and executed by the memory system. For some embodiments, the memory system starts a timer for the out-of-order command and monitors for the expiration of the timer for the out-of-order command. If the timer expires before the missing command is received by the memory system, the memory system can send a response to a host system that causes the host system to restart the sending of the sequence of commands starting from the first command in the sequence.