CPU oversubscription and new CPU jitter counters in Windows Server 2025

In the ever-evolving landscape of information technology, managing resources efficiently is paramount. With the advent of Windows Server 2025, an innovative approach to handling CPU oversubscription and jitter has been introduced, promising to enhance performance and reliability.

What is CPU oversubscription?​

CPU oversubscription occurs when more virtual processors (VPs) are allocated to virtual machines (VMs) than there are logical processors (LPs) available on the host machine. This technique is commonly used in virtualized environments to maximize resource utilization, improve cost efficiency, reduce data centers energy consumption and environmental impact. While this approach maximizes resource efficiency, it also introduces challenges related to balancing of compute resources and ensuring consistent performance for critical workloads which can be understood and mitigated through robust monitoring strategies.

Introducing new CPU jitter counters in Windows Server 2025​

To address the challenges posed by CPU oversubscription, Windows Server 2025 introduces new CPU jitter counters. These counters are designed to monitor and quantify the variability in CPU processing times, providing valuable insights into the performance of virtualized environments.

CPU jitter refers to the variation in the time it takes for a CPU to process a given workload. This variability can be caused by several factors, including CPU contention, interrupt handling, and other system activities. The new CPU jitter counters in Windows Server 2025 measure this variability, offering a detailed view of performance fluctuations.

\Hyper-V Hypervisor Virtual Processor(*)\CPU Wake Up Time Per Dispatch

\Hyper-V Hypervisor Root Virtual Processor(*)\CPU Wake Up Time Per Dispatch

Wakeup delay: The average amount of time a given VP had to wait for an idle LP to wake up and start running that VP when there is no contention for that LP. This counter estimated the amount of delay incurred by a VP when the system is overloaded.

\Hyper-V Hypervisor Virtual Processor(*)\CPU Contention Time Per Dispatch

\Hyper-V Hypervisor Root Virtual Processor(*)\CPU Contention Time Per Dispatch

Contention delay: The average amount of time a given VP had to spend waiting for an LP to run on that is attributed to VP contention, e.g. having to wait for other VPs to finish running first. This counter estimated the amount of delay incurred by a VP when the system is underloaded

Benefits of using CPU jitter counters​

The introduction of CPU jitter counters in Windows Server 2025 offers several key benefits:

• Improved performance management: By identifying the sources of CPU jitter, administrators can optimize resource allocation and reduce contention, leading to more stable and predictable performance.
• Enhanced troubleshooting: Detailed insights into CPU processing times enable quicker identification and resolution of performance bottlenecks and anomalies.
• Proactive monitoring: Visibility to CPU jitter allows for proactive management of resources, ensuring that potential issues are addressed before they affect service quality.