VCP-DCV vSphere Performance and Scaling Practice Question
A VM configured with 4 vCPUs shows high co-stop time in performance metrics. What does co-stop time indicate and which action should be taken to improve performance?
Answer choices
Why each option matters
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Reduce the number of vCPUs to match workload requirements
Co-stop time is time when the VM is ready to run but waiting for all vCPUs to be scheduled simultaneously. Reducing the number of vCPUs can alleviate this.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✓
Reduce the number of vCPUs to match workload requirements
Why this is correct
Co-stop measures time a vCPU spends ready but unable to run because its co-scheduled siblings are descheduled, typically from over-sized SMP virtual machines. Reducing vCPUs to match actual workload demand lowers scheduling skew and co-stop, improving throughput.
- ✗
Add more vCPUs to the VM
Why it's wrong here
Co-stop measures time a vCPU waits while its co-scheduled siblings are descheduled, so adding vCPUs widens the scheduling group and worsens the stall. More vCPUs suit genuinely parallel workloads that can saturate every core. Reducing vCPU count below the physical core count is the remedy here.
- ✗
Enable hyperthreading on the host
Why it's wrong here
Hyperthreading changes how the host presents logical processors; it does not alter the co-scheduling constraint that causes co-stop. The metric reflects a VM whose vCPU count exceeds available physical cores per NUMA node. Hyperthreading is enabled to raise host consolidation ratios, not to fix co-stop.
- ✗
Increase the VM's memory reservation
Why it's wrong here
Memory reservation guarantees RAM allocation and has no bearing on vCPU co-scheduling, which drives co-stop. The stall arises when sibling vCPUs cannot be run simultaneously on free physical cores. Reservations are used to prevent memory ballooning or swapping for latency-sensitive workloads.
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Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
This VCP-DCV practice question is part of Courseiva's free VMware certification practice question bank. Courseiva provides original exam-style practice questions with explanations, topic-based practice, mock exams, readiness tracking, and study analytics to help learners prepare for the VCP-DCV exam.