Virtual CPU Halt Latency Threshold Registers
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Solution Overview
Problem
In virtualized computer systems, the current halt/resume cycle for virtual CPUs incurs significant latency overhead due to hypervisor assumptions about guest latency needs, leading to inefficient CPU utilization and increased context switching.
Innovation Solution
Implementing input-output based virtual CPU halting by configuring halt registers with latency threshold values, allowing guests to communicate their latency needs to the hypervisor, which then determines the appropriate halt operation, reducing CPU utilization and improving efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If the hypervisor uses traditional halt/resume cycle with fixed assumptions about guest latency needs, then the virtual CPU can be halted to save resources, but this causes significant latency overhead and inefficient CPU utilization
Solution Approach 1:
The patent applies dynamics by making the halt operation flexible and adaptive rather than fixed. The hypervisor dynamically selects between different halt operations (polling, blocking, or running unrelated tasks) based on real-time guest latency needs communicated through halt registers. This allows the system to adapt the CPU management strategy to actual guest requirements, resolving the contradiction between resource savings and latency overhead.
Solution Approach 2:
The patent changes the parameter of halt operation type based on guest communication. By introducing halt registers that allow guests to specify their latency tolerance, the system transforms from using a fixed halt method to selecting from multiple halt operations (polling, blocking, unrelated tasks) depending on the parameter value provided by the guest. This parameter-driven approach optimizes both resource utilization and latency performance.
2Loss of time
If the hypervisor pins the physical CPU during halt polling to prevent context switching, then resume latency is reduced, but CPU utilization becomes inefficient and other tasks cannot execute
Solution Approach 1:
The patent applies dynamics by making the CPU pinning behavior conditional rather than fixed. Instead of always pinning the CPU during halt polling, the hypervisor dynamically decides whether to pin based on guest communication through halt registers. When guests indicate they can tolerate higher latency, the hypervisor avoids pinning and allows other tasks to execute, thus resolving the contradiction between fast resume and CPU utilization.
Solution Approach 2:
The patent changes the CPU pinning parameter based on guest latency tolerance. By introducing halt registers that communicate guest preferences, the system transforms from a fixed pinning strategy to a parameter-driven approach where the pinning duration and behavior are adjusted according to guest-specified latency requirements, optimizing both resume performance and overall CPU productivity.
3Device complexity
If the hypervisor makes assumptions about guest latency needs without guest input, then the halt operation can proceed without additional communication overhead, but the latency needs are not accurately met leading to inefficiency
Solution Approach 1:
The patent applies self-service by enabling guests to autonomously communicate their latency needs to the hypervisor through halt registers. Instead of the hypervisor making assumptions, the guest OS actively provides information about its requirements. This self-service mechanism resolves the contradiction by having guests take responsibility for expressing their needs, allowing the hypervisor to make informed decisions without complex communication protocols.
Data Source
AI summary
A hypervisor configures a plurality of halt registers, wherein each halt register of the plurality of halt registers is associated with a corresponding latency threshold value, and provides the plurality of halt registers to a guest operating system of a virtual machine. The hypervisor detects that the guest operating system of the virtual machine has accessed a halt register of the plurality of halt registers, determines a latency threshold value associated with the halt register accessed by the guest operating system, and performs a halt operation for a virtual processor of the virtual machine in view of the latency threshold value.