IOMMU Back-off Mechanism for Peripheral Page Request Log Overflow
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
The overflow of the peripheral page request (PPR) log in I/O memory management units (IOMMUs) leads to dropped requests, system instability, and performance degradation, as existing methods either risk losing system state or degrading performance by pausing I/O activity to avoid overflow.
Innovation Solution
Implementing a method in the IOMMU where a completion message is sent to peripherals indicating that a PPR is complete and discarding the request without queuing it in the PPR log when the available capacity is reached, and using delay queues to manage incoming requests and responses when the log is full.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If PPRs are queued in the PPR log, then system state is preserved, but log overflow causes request loss and system instability
Solution Approach 1:
The patent segments the request handling into two paths: requests are processed immediately without queuing when the system can handle them, and only overflow-critical requests are logged. This segmentation allows the system to maintain stability by preventing log overflow while still preserving necessary state information.
Solution Approach 2:
Instead of logging all PPRs (excessive action), the patent applies partial logging only when necessary to prevent overflow. The system performs the minimum necessary action to maintain stability without the overhead of logging every request, thus avoiding the contradiction between preserving state and preventing overflow.
2Reliability
If I/O activity is paused to avoid overflow, then log overflow is prevented, but system performance degrades
Solution Approach 1:
The patent monitors PPR log capacity in advance and takes preliminary action by discarding non-critical requests before overflow occurs. This prevents the need to pause I/O activity, as the system proactively manages log capacity by selectively dropping requests that are less critical to system state.
Solution Approach 2:
The patent applies different quality levels to different requests: critical requests are preserved in the log while non-critical requests are discarded. This local differentiation allows the system to prevent overflow without pausing overall I/O activity, maintaining performance while ensuring reliability for critical operations.
3Loss of information
If all PPRs are logged, then complete system state is maintained, but log capacity is exceeded and overflow occurs
Solution Approach 1:
The patent extracts only the essential elements needed for system state preservation from the full set of PPRs. By identifying and logging only critical requests while discarding redundant or less important ones, the system maintains necessary state information within log capacity constraints.
Solution Approach 2:
The patent changes the parameter of request retention by introducing a selective filtering mechanism. Instead of a binary all-or-nothing approach to logging, the system dynamically determines which requests to retain based on their importance to system state, effectively changing from a quantity-based to a quality-based retention strategy.
Data Source
AI summary
A system and method of managing requests from peripherals in a computer system are provided. In the system and method, an input/output memory management unit (IOMMU) receives a peripheral page request (PPR) from a peripheral. In response to a determination that a criterion regarding an available capacity of a PPR log is satisfied, a completion message is sent to the peripheral indicating that the PPR is complete and the PPR is discarded without queuing the PPR in the PPR log.