LPIC-1 System Architecture Practice Question
A Linux system administrator is tasked with setting up a new server that will host multiple virtual machines using KVM. The server has 64 GB of RAM and two physical CPUs, each with 8 cores (16 threads). The administrator needs to allocate resources efficiently. The VMs will have varying workloads. The administrator wants to ensure that the host system has enough resources for itself and that VMs can use all available CPU cores. Which approach should the administrator take to configure CPU allocation for the host and VMs?
⚠ Common exam trap
It's easy for candidates to assume overcommitting CPU resources is always safe (Option D) or that QEMU emulation is a performance improvement (Option A), when in fact KVM's hardware acceleration and proper pinning are critical for efficient virtualization.
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
✓
Use CPU pinning to reserve two physical cores for the host and distribute the remaining cores among VMs using host-passthrough mode.
It reserves two physical cores for the host system to ensure its stability and performance, while distributing the remaining cores among VMs using CPU pinning and host-passthrough mode. This approach allows VMs to access the full CPU feature set and all available cores efficiently, balancing host overhead with VM resource needs in a KVM environment.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
Use QEMU emulation instead of KVM to reduce CPU overhead.
Why it's wrong here
QEMU emulation interprets guest instructions in software rather than executing them directly on the host CPU via KVM's hardware virtualisation extensions, so throughput drops sharply and the goal of using all physical cores efficiently is defeated. Emulation is tempting when running guest code compiled for a different CPU architecture.
- ✗
Pin all physical CPU cores to the VMs using virsh vcpupin, and leave no cores for the host.
Why it's wrong here
Pinning every physical core to guests leaves the host no CPU time for its own kernel, hypervisor and management tasks, risking host instability and unresponsive VMs. Pinning is tempting for latency-sensitive workloads needing deterministic, uncontended core access, but the host must retain reserved cores.
- ✓
Use CPU pinning to reserve two physical cores for the host and distribute the remaining cores among VMs using host-passthrough mode.
Why this is correct
CPU pinning dedicates two physical cores to the host, guaranteeing its resources, while host-passthrough exposes remaining cores so VMs access all available CPU features. This matches the stem's dual constraints: host reservation plus full core availability.
- ✗
Overcommit CPU resources by assigning 32 vCPUs to each VM, relying on the hypervisor to schedule.
Why it's wrong here
Assigning 32 vCPUs per VM vastly exceeds the host's 16 threads, so the hypervisor cannot deliver the promised parallelism and the host itself is starved of scheduling time. Overcommit is tempting for consolidating many lightly loaded VMs, where average utilisation stays low.
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Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
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