Understanding Affinity in Virtualization: VM Affinity, CPU Pinning, and NUMA Affinity

In virtualization and NFV environments, affinity refers to how workloads (virtual machines, VNFs, or processes) are bound to specific hardware resources. Affinity policies are critical for optimizing performance, ensuring predictable latency, and balancing workloads across the infrastructure. Let’s explore the main types:

1. VM Affinity and Anti-Affinity

• VM Affinity: Ensures that certain VMs always run on the same physical host. This is useful when VNFs or applications require low-latency communication between them.

• VM Anti-Affinity: Ensures that specific VMs run on different hosts. This improves resiliency — if one host fails, not all critical VMs are lost.

Pros: Better control of workload placement.
Cons: Can reduce flexibility of the orchestrator when resources are tight.

2. CPU Pinning (vCPU to pCPU Affinity)

CPU pinning is the practice of binding a virtual CPU (vCPU) to a specific physical CPU core (pCPU). Instead of letting the hypervisor dynamically schedule vCPUs across all available cores, pinning provides a fixed mapping.

• Use Case: Real-time VNFs (e.g., packet processing, firewalls) where jitter and latency must be minimized.

• Pros: Predictable performance and reduced CPU scheduling overhead.

• Cons: Less efficient use of CPU resources if workloads are uneven.

3. NUMA Affinity

Modern servers are often built with Non-Uniform Memory Access (NUMA) architectures, where memory is divided across CPU sockets. NUMA affinity ensures that a VM’s vCPUs and memory are placed within the same NUMA node, minimizing cross-socket memory access delays.

• Use Case: High-performance VNFs like EPC or 5G Core functions that are memory-intensive.

• Pros: Improves throughput and reduces memory latency.

• Cons: Misconfiguration can lead to performance degradation.

4. Network Affinity

While less common in terminology, some deployments also enforce network affinity to ensure VMs or VNFs are located close to specific network interfaces or data paths, improving packet processing performance.

Why Affinity Matters

Affinity policies allow operators to balance performance, resiliency, and efficiency:

• VM Affinity/Anti-affinity → Focus on workload placement.

• CPU Pinning → Focus on CPU determinism.

• NUMA Affinity → Focus on memory locality.

Conclusion

In NFV and virtualization, affinity is about control. By carefully applying VM affinity, CPU pinning, and NUMA affinity, operators can fine-tune performance for demanding telecom workloads while balancing flexibility and resource utilization. As networks evolve toward cloud-native, these concepts still inspire placement policies in Kubernetes for CNFs.