Guest OS Interrupt Coalescing Latency Reduction
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Solution Overview
Problem
Interrupt coalescing in virtualized computer systems increases latency and idle time, leading to wasted CPU resources and decreased operational throughput, as it defers interrupt delivery until a predetermined number of interrupts are queued or an interval timer triggers.
Innovation Solution
A guest operating system proactively requests coalesced interrupts from a hypervisor by monitoring the execution state of applications and temporarily disabling or immediately delivering queued interrupts when the application becomes idle, allowing for reduced latency without disrupting the application's workflow.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If interrupt coalescing is used to reduce interrupt load, then interrupt delivery frequency is reduced, but latency increases and CPU idle time increases
Solution Approach 1:
The patent dynamically adjusts interrupt coalescing parameters based on application state. When the application is idle, coalescing is maintained to reduce CPU wakeups. When the application becomes active, coalescing is reduced or disabled to minimize latency. This dynamic adaptation resolves the contradiction by making the system behavior context-dependent rather than static.
Solution Approach 2:
The system implements feedback mechanisms by monitoring application activity state and using this information to adjust interrupt coalescing behavior. The guest OS or hypervisor detects application idle states and responds by modifying interrupt delivery timing, creating a closed-loop control system that balances energy efficiency with responsiveness based on real-time conditions.
2Device complexity
If interrupt coalescing defers interrupt delivery until a predetermined number of interrupts are queued, then interrupt load on virtual machine is reduced, but operational throughput decreases
Solution Approach 1:
The patent implements dynamic adjustment of coalescing parameters based on system state. Rather than using fixed coalescing thresholds, the system adapts the number of interrupts to coalesce or the time interval between coalesced interrupts based on application activity detection. This allows the system to maintain low processing complexity during idle periods while restoring throughput during active periods.
3Loss of energy
If interrupt coalescing uses an interval timer to defer interrupt delivery, then interrupt frequency is reduced, but application response time increases
Solution Approach 1:
The system uses feedback from application state monitoring to dynamically adjust interrupt coalescing behavior. When the application transitions from idle to active state, the system detects this change and adjusts the coalescing interval or disables coalescing temporarily, ensuring that interrupt response time meets application requirements while still providing energy savings during idle periods.
Data Source
AI summary
A guest operating system of a virtual machine sends a request to a hypervisor to coalesce interrupts from a networking device. The guest operating system then monitors the execution state of an application on the virtual machine to detect when the application becomes idle. Upon detecting that the application is idle, the guest operating system can send a request to the hypervisor for any coalesced interrupts that have been queued for delivery to the application. The guest operating system may then receive the coalesced interrupts from the hypervisor and deliver them to the application.