PCI Interrupt Line Management for Faulty Device Isolation
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Solution Overview
Problem
Managing interrupts from multiple PCI devices sharing a single interrupt line is inefficient, particularly when a faulty device or driver bug causes the interrupt line to remain asserted, leading to unhandled interrupts and system instability.
Innovation Solution
The system disables interrupts for all devices on the shared line, periodically enables interrupts for a subset, increments a counter for devices within the subset if an unhandled interrupt persists, and avoids enabling interrupts for devices with counter values exceeding a threshold, effectively isolating the faulty device.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If multiple PCI devices share the same interrupt line, then device complexity is reduced and resource utilization is improved, but interrupt management efficiency deteriorates and system reliability decreases when faulty devices cause unhandled interrupts
Solution Approach 1:
The patent segments the set of PCI devices sharing an interrupt line into multiple subsets and processes them iteratively. In each iteration, a subset is selected, interrupt ability is enabled for devices in that subset, and counters are incremented for devices that generate unhandled interrupts. This segmentation allows the system to isolate faulty devices without disabling interrupts for all devices simultaneously, thereby maintaining reliability while preserving the benefit of shared interrupt lines.
Solution Approach 2:
The patent implements a feedback mechanism using counters for each device. When an unhandled interrupt is detected after enabling interrupts for a subset, the counters for devices in that subset are incremented. This feedback information is used in subsequent iterations to identify and isolate faulty devices. The feedback loop continues until all faulty devices are identified or the counter threshold is reached, ensuring system reliability is maintained while allowing interrupt sharing.
2Ease of operation
If interrupt ability is enabled for all devices on a shared interrupt line, then device functionality is maintained, but unhandled interrupts from faulty devices cause system instability
Solution Approach 1:
The patent dynamically adjusts interrupt ability for different subsets of devices in an iterative manner. Instead of a static all-or-nothing approach, the system dynamically enables interrupts for selected subsets, monitors for unhandled interrupts, and adjusts the configuration based on feedback. This dynamic approach allows the system to maintain device functionality for good devices while isolating faulty ones, thereby ensuring system stability.
Solution Approach 2:
The patent divides the set of devices into multiple subsets and processes them iteratively. In each iteration, a subset is selected and interrupt ability is enabled only for devices in that subset, not all devices simultaneously. This segmentation allows the system to maintain functionality for devices in the current subset while isolating potentially faulty devices in other subsets, balancing ease of operation with system reliability.
3Reliability
If the system periodically checks and manages interrupt ability for all devices, then faulty devices can be identified, but system performance decreases due to continuous monitoring and counter increments
Solution Approach 1:
The patent segments devices into subsets and processes them iteratively, checking for unhandled interrupts only when necessary. This segmentation allows the system to identify faulty devices without continuously monitoring all devices, thereby maintaining reliability while minimizing performance impact. The iterative process continues until faulty devices are identified or the counter threshold is reached.
Solution Approach 2:
The patent implements periodic checking of interrupt ability and counter values at defined intervals. Instead of continuous monitoring, the system performs periodic actions to identify faulty devices. This periodic approach allows the system to maintain reliability by periodically checking for unhandled interrupts while minimizing performance degradation associated with constant monitoring and processing.
Data Source
AI summary
A method performed by a physical computing system includes, with the computing system, determining a set of devices that share a Peripheral Component Interconnect (PCI) interrupt line, with the computing system, disabling interrupt ability for each device within the set, with the computing system, selecting a first subset of devices within the set, with the computing system, enabling interrupt ability for each of the devices within the first subset, and with the computing system, in response to detecting an unhandled interrupt after enabling interrupt ability for the devices within the first subset, incrementing a counter for each device within the first subset.