# CPU Model
## What is a CPU Model
In space.vars.product\_name, a CPU model refers to the set of CPU features and flags exposed to a virtual machine. This is how space.vars.product\_name compute service manages the CPU architecture presented to a virtual machine guest operating system, allowing for flexibility and control over performance, compatibility, and migration capabilities.
## Use Cases for CPU Model
* **Performance:** Exposing specific CPU features can maximize the performance of workloads running inside the virtual machines.
* **Compatibility:** Ensuring consistent behavior across different hypervisor hosts in a virtualized cluster, regardless of the underlying host CPU, can be achieved by specifying a CPU model.
* **Migration:** CPU models play an important role in [Live Migration](/private-cloud-director/2026.1/virtualized-clusters/virtualmachine/vm-migration.md#live-migration) and [Dynamic Resource Rebalancing Drr ](/private-cloud-director/2026.1/virtualized-clusters/virtualized-cluster/dynamic-resource-rebalancing-drr.md). Matching CPU models on source and destination hosts is crucial for successful live migration and for [Dynamic Resource Rebalancing Drr ](/private-cloud-director/2026.1/virtualized-clusters/virtualized-cluster/dynamic-resource-rebalancing-drr.md)to operate with full efficiency.
## Locating CPU Models Supported By Your Host
The libvirt KVM driver that comes built in as part of your Ubuntu installation on your hypervisor host provides a number of standard CPU model names.
These models are defined in `/usr/share/libvirt/cpu_map/*.xml`. You can inspect these files to determine which models are supported by your server.
Each file located under this directory contains information about the **feature set provided by the CPU model.**
For example, here the file `x86_SandyBridge-IBRS.xml`describes the CPU vendor, family, model and features supported by the SandyBridge-IBRS CPU Model.
{% tabs %}
{% tab title="Bash" %}
```bash
$ cat /usr/share/libvirt/cpu_map/x86_SandyBridge-IBRS.xml
...
```
{% endtab %}
{% endtabs %}
You can also locate the supported CPU models by running `virsh cpu-models ` command:
{% tabs %}
{% tab title="Bash" %}
```bash
$ virsh cpu-models x86_64
...
SandyBridge
SandyBridge-IBRS
IvyBridge
IvyBridge-IBRS
Haswell-noTSX
Haswell-noTSX-IBRS
Haswell
Haswell-IBRS
```
{% endtab %}
{% endtabs %}
## Supported CPU Models
space.vars.product\_name currently supports following list of [Supported Cpu Models List](/private-cloud-director/2026.1/virtualized-clusters/add-hosts-virtualized-cluster/cpu-model/supported-cpu-models-list.md).
## CPU Model Configuration Per Host
When you configure a host with 'hypervisor' role, here are the steps followed by the compute service to configure the CPU model on the host:
1. It starts by checking the [list of approved models](/private-cloud-director/2026.1/virtualized-clusters/add-hosts-virtualized-cluster/cpu-model/supported-cpu-models-list.md), beginning with the newest models based on the CPU vendor for your host.
2. For each model, it verifies compatibility by checking if the model is marked as **usable** in the `virsh -c qemu:///system domcapabilities` output.
3. The first approved model marked as usable is selected.
4. If no approved models are usable, the system falls back to a generic model.
## CPU Model Pre-requisites for Hypervisor Hosts
* Each host that you authorize in your space.vars.product\_name setup with 'hypervisor' role must support at least one CPU Model that is part of the [Supported Cpu Models List](/private-cloud-director/2026.1/virtualized-clusters/add-hosts-virtualized-cluster/cpu-model/supported-cpu-models-list.md) list.
* Failing this requirement may result in unexpected errors such as the host going to offline state, or virtual machines failing to provision, etc.
## CPU Model Pre-requisites for Migration
Following CPU model prerequisites must be met by all hosts within a virtualized cluster, so that operations like live migration, cold migration, VM evacuation can work smoothly, and services like [Dynamic Resource Rebalancing Drr ](/private-cloud-director/2026.1/virtualized-clusters/virtualized-cluster/dynamic-resource-rebalancing-drr.md), [Virtual Machine High Availability Vm Ha ](/private-cloud-director/2026.1/virtualized-clusters/virtualized-cluster/virtual-machine-high-availability-vm-ha.md)can operate efficiently.
* All hosts in the cluster must have the exact same value for the most recent CPU model supported. Read here for how [system configures CPU model per host](#cpu-model-configuration-per-host).
* This value must be part of the list of [Supported Cpu Models List](/private-cloud-director/2026.1/virtualized-clusters/add-hosts-virtualized-cluster/cpu-model/supported-cpu-models-list.md).
* If the hosts do not all report the same most-recent supported CPU model, or if a host’s CPU model is missing from the supported models list above, then you can set the [CPU Mode and Model](/private-cloud-director/2026.1/virtualized-clusters/virtualized-cluster.md#cpu-mode-and-model)
---
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