Predictive Virtual Machine Halt Timer Mechanism

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Solution Overview

Problem

Existing virtualization systems face high latency and inefficient CPU usage when handling low-frequency interrupts, as current methods like idle-polling and repeated VM reentries waste CPU cycles and fail to effectively manage VM exits and entries.

Innovation Solution

A predictive virtual machine halt system where a hypervisor starts a timer after receiving a VCPU halt request, allowing another task to run on the host CPU until the timer expires, then restarting the VCPU, thereby optimizing CPU usage and reducing latency by predicting interrupt arrival times.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Speed

If the hypervisor immediately restarts the VCPU upon receiving a halt request, then the response time to interrupts is improved, but the CPU utilization deteriorates due to wasted cycles during idle periods

Engineering Contradiction:

Improveinterrupt response timeVSAvoidCPU utilization

Core Design Contradiction:

SpeedVSProductivity

Solution Approach 1:

The hypervisor performs a preliminary action by starting a timer when the VCPU halts, predicting that the interrupt will arrive within a predetermined time window. This allows the system to proactively manage the VCPU state rather than reactively responding to interrupts, optimizing both response time and CPU utilization by avoiding premature VCPU restarts.

Inventive Principle:

Principle #10Preliminary action

2Reliability

If the hypervisor keeps the VCPU running continuously, then the interrupt handling capability is improved, but the CPU waste increases due to idle polling

Engineering Contradiction:

Improveinterrupt handling capabilityVSAvoidCPU waste

Core Design Contradiction:

ReliabilityVSLoss of energy

Solution Approach 1:

The system implements periodic action by using a timer to periodically check whether the predicted interrupt time has been reached before restarting the VCPU. This periodic mechanism replaces continuous idle polling with efficient timer-based monitoring, reducing CPU waste while maintaining reliable interrupt handling capability.

Inventive Principle:

Principle #19Periodic action

3Measurement precision

If the hypervisor uses traditional idle-polling methods, then the interrupt detection is improved, but the latency increases due to repeated VM exits and entries

Engineering Contradiction:

Improveinterrupt detection accuracyVSAvoidVM exit/entry latency

Core Design Contradiction:

Measurement precisionVSLoss of time

Solution Approach 1:

The timer acts as an intermediary between the halted VCPU and the hypervisor's interrupt handling mechanism. Instead of repeatedly exiting and reentering the VM to check for interrupts, the hypervisor uses the timer to predict and coordinate interrupt arrival, eliminating frequent VM exits/entries and reducing latency while maintaining accurate interrupt detection.

Inventive Principle:

Principle #24Intermediary (Mediator)

Data Source

PatentUS10437308B2Predictive virtual machine halt

Publication Date: 2019.10.08 RED HAT INC

AI summary

A system and method for predictive virtual machine halt includes a memory, a host central processing unit (CPU) in communication with the memory, a hypervisor executing on the host CPU, and a virtual machine executing on the hypervisor. The virtual machine includes a virtual central processing unit (VCPU) and a guest. In an example, the hypervisor starts executing the VCPU on the host CPU. When the hypervisor detects a request to stop executing the VCPU from the guest, the hypervisor starts a timer associated with the host CPU. A predetermined amount of time is set in the timer. Then, the hypervisor stops executing the VCPU and starts executing a task on the host CPU while the timer is running. When the hypervisor detects an expiration of the timer, the hypervisor stops executing the task on the host CPU and restarts executing the VCPU on the host CPU.