Interrupt Coalescing for Storage Virtual Function
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Solution Overview
Problem
In virtualization scenarios, high input/output (IO) rates lead to significant processor overhead due to frequent interrupts, which can result in resource shortages, especially when multiple virtual machines share a single multi-processor system, and existing interrupt coalescing techniques are inefficient in hypervisor environments.
Innovation Solution
A method for coalescing IO interrupts to virtual machines by determining whether the virtual machine has responded to a previous interrupt, using a shared memory space for communication between the guest operating system and the virtualization intermediary to decide on interrupt delivery or coalescing based on IO completion queue fill levels and latency measures.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of time
If interrupt coalescing is implemented in hardware controllers with fine-grained timers, then IO latency is bounded, but the system becomes inefficient to use in a hypervisor environment
Solution Approach 1:
The patent introduces a shared memory space as an intermediary between the guest operating system and the virtualization intermediary. This shared memory enables efficient communication and coordination for interrupt coalescing decisions without requiring complex timer mechanisms in the hypervisor, thus maintaining low latency while improving hypervisor efficiency.
2Use of energy by moving object
If interrupt coalescing is used to limit the number of interrupts, then processor overhead is reduced, but IO latency increases
Solution Approach 1:
The patent implements a feedback mechanism where the guest operating system writes information to shared memory indicating whether the IO completion queue has reached an unsafe fill level. The virtualization intermediary reads this information and makes informed decisions about interrupt delivery, dynamically balancing processor overhead reduction with latency maintenance based on real-time queue status.
3Productivity
If multiple virtual machines share a single multi-processor system, then resource utilization improves, but processor overhead from frequent interrupts increases
Solution Approach 1:
The patent merges interrupt handling operations across multiple virtual machines by implementing interrupt coalescing at the virtualization intermediary level. Multiple IO completions from different VMs can be coalesced into a single interrupt delivery when safe, reducing the total number of interrupts processed by the multi-processor system while maintaining efficient resource utilization.
Data Source
AI summary
A method is described for coalescing input/output (IO) interrupts to a virtual machine (VM) running on a host computer. At a virtualization layer of the host computer that supports execution of the VM receives an IO interrupt in response to a completion of an IO request of the VM, wherein a transmission of the IO request by the VM to an IO device bypasses the virtualization layer. The virtualization layer then determines whether the VM has responded to a most recently delivered IO interrupt to the VM by the virtualization layer, and drops the IO interrupt if the VM has not responded to the most recently delivered IO interrupt, thereby failing to deliver the IO interrupt to the VM.