Pessimistic Interrupt Affinity for Virtual Processors
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Solution Overview
Problem
In modern computer systems with multiple processors, the overhead of inter-processor interrupts (IPIs) is significant due to the need for one processor to forward device interrupts to another, leading to inefficiencies in interrupt handling and response times.
Innovation Solution
A method and system that reconfigures device interrupts to eliminate the need for inter-processor communications by updating the device and interrupt controller to send future interrupts directly to the processor handling the virtual processor controlling the device, based on criteria such as IPI thresholds and virtual processor migrations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If the host scheduler assigns device interrupts to one hardware processor and the virtual machine scheduler assigns virtual processors to handle device interrupts on a different hardware processor, then the system can balance work load between processors and provide virtualization flexibility, but inter-processor interrupts are generated introducing overhead for interrupt processing
Solution Approach 1:
The patent applies preliminary action by proactively tracking the mapping between virtual processors and hardware processors, and pre-configuring interrupt routing before interrupts occur. When a virtual processor is assigned to handle device interrupts, the system proactively updates the device or interrupt controller to route interrupts directly to the appropriate hardware processor, avoiding the need for inter-processor interrupt forwarding and eliminating the time loss associated with IPI overhead.
2Ease of operation
If interrupts are forwarded between processors, then virtual processors can be assigned to handle device interrupts on the processor they run on, but this generates inter-processor interrupts that introduce overhead
Solution Approach 1:
The patent implements feedback by continuously monitoring the assignment of virtual processors to hardware processors and using this information to dynamically adjust interrupt routing. The system tracks which virtual processor is assigned to handle interrupts from which device, and when mappings change, it provides feedback to update the interrupt controller or device configuration accordingly. This ensures interrupts are always routed to the correct processor without requiring IPI forwarding, maintaining both correctness and efficiency.
3Adaptability or versatility
If the system maintains separate schedulers for host and virtual machine, then each can independently manage its own work load balancing, but this leads to mismatched interrupt assignments and increased inter-processor communication
Solution Approach 1:
The patent introduces an intermediary mechanism that bridges the host scheduler and virtual machine scheduler. This intermediary tracks the mappings between virtual processors and hardware processors, and uses this information to coordinate interrupt routing decisions. By acting as a mediator, it allows both schedulers to maintain their independence and work load balancing autonomy while ensuring that interrupt assignments are consistent with the current virtual processor to hardware processor mappings, avoiding the complexity of direct coordination between the two schedulers.
Data Source
AI summary
A computing apparatus identifies that a first processor of a host has forwarded information for a device to a second processor that controls the device. After identifying that the first processor has forwarded the information to the second processor and in response to determining that one or more update criteria have been satisfied, the computing apparatus causes future information for the device to be forwarded to the second processor.