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:
hv.FEATURES.RDT.RDT_ENABLEDto y to enable RDT
hv.FEATURES.RDT.CDP_ENABLEDto n to disable CDP. vCAT requires CDP to be disabled.
hv.FEATURES.RDT.VCAT_ENABLEDto 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:
vm.virtual_cat_supportto ‘y’ to enable the vCAT feature on the VM.
vm.clos.vcpu_closto assign COS IDs to the VM.
GUEST_FLAG_VCAT_ENABLEDis not specified for a VM (abbreviated as RDT VM):
vcpu_closis 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.
GUEST_FLAG_VCAT_ENABLEDis specified for a VM (abbreviated as vCAT VM):
vcpu_closis 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>
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.