Enable vCAT Configuration¶

vCAT is built on top of RDT, so to use vCAT we must first enable RDT. For details on enabling RDT configuration on ACRN, see Enable RDT Configuration. For details on ACRN vCAT high-level design, see Enable vCAT.

The vCAT feature is disabled by default in ACRN. You can enable vCAT via the UI, the steps listed below serve as an FYI to show how those settings are translated into XML in the scenario file:

Configure system level features:

Edit hv.FEATURES.RDT.RDT_ENABLED to y to enable RDT
Edit hv.FEATURES.RDT.CDP_ENABLED to n to disable CDP. Currently vCAT requires CDP to be disabled.

Edit hv.FEATURES.RDT.VCAT_ENABLED to y to enable vCAT

<FEATURES>
    <RDT>
        <RDT_ENABLED>y</RDT_ENABLED>
        <CDP_ENABLED>n</CDP_ENABLED>
        <VCAT_ENABLED>y</VCAT_ENABLED>
        <CLOS_MASK></CLOS_MASK>
    </RDT>
</FEATURES>

In each Guest VM configuration:
- Edit vm.guest_flags.guest_flag and add GUEST_FLAG_VCAT_ENABLED to enable the vCAT feature on the VM.
- Edit vm.clos.vcpu_clos to assign COS IDs to the VM.
  
  If GUEST_FLAG_VCAT_ENABLED is not specified for a VM (abbreviated as RDT VM): vcpu_clos is per CPU in a VM and it configures each CPU in a VM to a desired COS ID. So the number of vcpu_closes is equal to the number of vCPUs assigned.
  
  If GUEST_FLAG_VCAT_ENABLED is specified for a VM (abbreviated as vCAT VM): vcpu_clos is not per CPU anymore; instead, it specifies a list of physical COS IDs (minimum 2) that are assigned to a vCAT VM. The number of vcpu_closes is not necessarily equal to the number of vCPUs assigned, but may be not only greater than the number of vCPUs assigned but less than this number. Each vcpu_clos will be mapped to a virtual COS ID, the first vcpu_clos is mapped to virtual COS ID 0 and the second is mapped to virtual COS ID 1, etc.
```
<vm id="1">
  <guest_flags>
    <guest_flag>GUEST_FLAG_VCAT_ENABLED</guest_flag>
  </guest_flags>
  <cpu_affinity>
      <pcpu_id>1</pcpu_id>
      <pcpu_id>2</pcpu_id>
  </cpu_affinity>
  <clos>
    <vcpu_clos>2</vcpu_clos>
    <vcpu_clos>4</vcpu_clos>
    <vcpu_clos>5</vcpu_clos>
    <vcpu_clos>7</vcpu_clos>
  </clos>
</vm>
```
  Note
  
  CLOS_MASK defined in scenario file is a capacity bitmask (CBM) starting at bit position low (the lowest assigned physical cache way) and ending at position high (the highest assigned physical cache way, inclusive). As CBM only allows contiguous ‘1’ combinations, so CLOS_MASK essentially is the maximum CBM that covers all the physical cache ways assigned to a vCAT VM.
  
  The config tool imposes oversight to prevent any problems with invalid configuration data for vCAT VMs:
  - For a vCAT VM, its vcpu_closes cannot be set to 0, COS ID 0 is reserved to be used only by hypervisor
  - There should not be any COS ID overlap between a vCAT VM and any other VMs. e.g. the vCAT VM has exclusive use of the assigned COS IDs
  - For a vCAT VM, each vcpu_clos must be less than L2/L3 COS_MAX
  - For a vCAT VM, its vcpu_closes cannot contain duplicate values
Follow instructions in Getting Started Guide and build with this XML configuration.