COA Performance Optimization 3

Question 1

Which Nova configuration option allows CPU overcommit ratios to be set, enabling more vCPUs than physical cores on a host?

Accepted Answer

cpu_allocation_ratio

Answer

cpu_allocation_ratio multiplies reported physical CPUs by the given factor, allowing Nova to schedule more vCPUs than physically available.

Question 2

What Neutron mechanism driver provides the best network I/O performance for bare-metal-like workloads using kernel bypass?

Accepted Answer

SR-IOV with ml2 sriovnicswitch

Answer

SR-IOV passes virtual functions directly to instances, bypassing the hypervisor network stack for near-native throughput and lowest latency.

Question 3

In a Ceph-backed Glance deployment, which image format eliminates the conversion overhead during Nova instance boot?

Accepted Answer

raw

Answer

Raw images are directly usable by Ceph RBD without any conversion, so Nova boots instances from them without a CPU-intensive format conversion step.

Question 4

Which Heat resource type should be used to implement auto-scaling policies based on Ceilometer/Aodh alarms?

Accepted Answer

OS::Heat::AutoScalingGroup

Answer

OS::Heat::AutoScalingGroup manages a group of resources that can grow or shrink in response to OS::Heat::ScalingPolicy actions triggered by alarms.

Question 5

What is the primary performance benefit of enabling NUMA topology awareness in Nova when scheduling instances?

Accepted Answer

Instances are placed so their vCPUs and memory reside on the same NUMA node, minimizing cross-node memory latency

Answer

NUMA-aware scheduling ensures that instance vCPUs access memory on the same NUMA node, avoiding expensive cross-node memory transfers.

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