Chapter 15. Configuring real-time compute As a cloud administrator, you might need instances on your Compute nodes to adhere to low-latency policies and perform real-time processing. Real-time Compute nodes include a real-time capable kernel, specific virtualization modules, and optimized deployment parameters, to facilitate real-time processing requirements and minimize latency. The process to enable Real-time Compute includes: configuring the BIOS settings of the Compute nodes building a real-time image with real-time kernel and Real-Time KVM (RT-KVM) kernel module assigning the ComputeRealTime role to the Compute nodes For a use-case example of real-time Compute deployment for NFV workloads, see the Example: Configuring OVS-DPDK with ODL and VXLAN tunnelling section in the Network Functions Virtualization Planning and Configuration Guide . Note Real-time Compute nodes are supported only with Red Hat Enterprise Linux version 7.5 or later. 15.1. Preparing Compute nodes for real-time Before you can deploy Real-time Compute in your overcloud, you must enable Red Hat Enterprise Linux Real-Time KVM (RT-KVM), configure your BIOS to support real-time, and build the real-time overcloud image. Prerequisites You must use Red Hat certified servers for your RT-KVM Compute nodes. See Red Hat Enterprise Linux for Real Time 7 certified servers for details. You need a separate subscription to Red Hat OpenStack Platform for Real Time to access the rhel-8-for-x86_64-nfv-rpms repository. For details on managing repositories and subscriptions for your undercloud, see Registering the undercloud and attaching subscriptions in the Director Installation and Usage guide. Procedure To build the real-time overcloud image, you must enable the rhel-8-for-x86_64-nfv-rpms repository for RT-KVM. To check which packages will be installed from the repository, enter the following command: To build the overcloud image for Real-time Compute nodes, install the libguestfs-tools package on the undercloud to get the virt-customize tool: Important If you install the libguestfs-tools package on the undercloud, disable iscsid.socket to avoid port conflicts with the tripleo_iscsid service on the undercloud: Extract the images: Copy the default image: Register the image and configure the required subscriptions: Replace the username and password values with your Red Hat customer account details. For general information about building a Real-time overcloud image, see the knowledgebase article Modifying the Red Hat Enterprise Linux OpenStack Platform Overcloud Image with virt-customize . Find the SKU of the Red Hat OpenStack Platform for Real Time subscription. The SKU might be located on a system that is already registered to the Red Hat Subscription Manager with the same account and credentials: Attach the Red Hat OpenStack Platform for Real Time subscription to the image: Create a script to configure rt on the image: Run the script to configure the real-time image: Re-label SELinux: Extract vmlinuz and initrd . For example: Note The software version in the vmlinuz and initramfs filenames vary with the kernel version. Upload the image: You now have a real-time image you can use with the ComputeRealTime composable role on select Compute nodes. To reduce latency on your Real-time Compute nodes, you must modify the BIOS settings in the Compute nodes. You should disable all options for the following components in your Compute node BIOS settings: Power Management Hyper-Threading CPU sleep states Logical processors See Setting BIOS parameters for descriptions of these settings and the impact of disabling them. See your hardware manufacturer documentation for complete details on how to change BIOS settings. 15.2. Deploying the Real-time Compute role Red Hat OpenStack Platform (RHOSP) director provides the template for the ComputeRealTime role, which you can use to deploy real-time Compute nodes. You must perform additional steps to designate Compute nodes for real-time. Procedure Based on the /usr/share/openstack-tripleo-heat-templates/environments/compute-real-time-example.yaml file, create a compute-real-time.yaml environment file that sets the parameters for the ComputeRealTime role. The file must include values for the following parameters: IsolCpusList and NovaComputeCpuDedicatedSet : List of isolated CPU cores and virtual CPU pins to reserve for real-time workloads. This value depends on the CPU hardware of your real-time Compute nodes. NovaComputeCpuSharedSet : List of host CPUs to reserve for emulator threads. KernelArgs : Arguments to pass to the kernel of the Real-time Compute nodes. For example, you can use default_hugepagesz=1G hugepagesz=1G hugepages=<number_of_1G_pages_to_reserve> hugepagesz=2M hugepages=<number_of_2M_pages> to define the memory requirements of guests that have huge pages with multiple sizes. In this example, the default size is 1GB but you can also reserve 2M huge pages. NovaComputeDisableIrqBalance : Ensure that this parameter is set to true for Real-time Compute nodes, because the tuned service manages IRQ balancing for real-time deployments instead of the irqbalance service. Add the ComputeRealTime role to your roles data file and regenerate the file. For example: This command generates a ComputeRealTime role with contents similar to the following example, and also sets the ImageDefault option to overcloud-realtime-compute . For general information about custom roles and about the roles-data.yaml , see Roles . Create the compute-realtime flavor to tag nodes that you want to designate for real-time workloads. For example: Tag each node that you want to designate for real-time workloads with the compute-realtime profile. Map the ComputeRealTime role to the compute-realtime flavor by creating an environment file with the following content: Add your environment files and the new roles file to the stack with your other environment files and deploy the overcloud: 15.3. Sample deployment and testing scenario The following example procedure uses a simple single-node deployment to test that the environment variables and other supporting configuration is set up correctly. Actual performance results might vary, depending on the number of nodes and instances that you deploy in your cloud. Procedure Create the compute-real-time.yaml file with the following parameters: Create a new rt_roles_data.yaml file with the ComputeRealTime role: Add compute-real-time.yaml and rt_roles_data.yaml to the stack with your other environment files and deploy the overcloud: This command deploys one Controller node and one Real-time Compute node. Log into the Real-time Compute node and check the following parameters: 15.4. Launching and tuning real-time instances After you deploy and configure Real-time Compute nodes, you can launch real-time instances on those nodes. You can further configure these real-time instances with CPU pinning, NUMA topology filters, and huge pages. Prerequisites The compute-realtime flavor exists on the overcloud, as described in Deploying the Real-time Compute role . Procedure Launch the real-time instance: Optional: Verify that the instance uses the assigned emulator threads: Pinning CPUs and setting emulator thread policy To ensure that there are enough CPUs on each Real-time Compute node for real-time workloads, you need to pin at least one virtual CPU (vCPU) for an instance to a physical CPU (pCPUs) on the host. The emulator threads for that vCPU then remain dedicated to that pCPU. Configure your flavor to use a dedicated CPU policy. To do so, set the hw:cpu_policy parameter to dedicated on the flavor. For example: Note Make sure that your resources quota has enough pCPUs for the Real-time Compute nodes to consume. Optimizing your network configuration Depending on the needs of your deployment, you might need to set parameters in the network-environment.yaml file to tune your network for certain real-time workloads. To review an example configuration optimized for OVS-DPDK, see the Configuring the OVS-DPDK parameters section of the Network Functions Virtualization Planning and Configuration Guide . Configuring huge pages It is recommended to set the default huge pages size to 1GB. Otherwise, TLB flushes might create jitter in the vCPU execution. For general information about using huge pages, see the Running DPDK applications web page. Disabling Performance Monitoring Unit (PMU) emulation Instances can provide PMU metrics by specifying an image or flavor with a vPMU. Providing PMU metrics introduces latency. Note The vPMU defaults to enabled when NovaLibvirtCPUMode is set to host-passthrough . If you do not need PMU metrics, then disable the vPMU to reduce latency by setting the PMU property to "False" in the image or flavor used to create the instance: Image: hw_pmu=False Flavor: hw:pmu=False

Commands:
dnf repo-pkgs rhel-8-for-x86_64-nfv-rpms list Loaded plugins: product-id, search-disabled-repos, subscription-manager Available Packages kernel-rt.x86_64 4.18.0-80.7.1.rt9.153.el8_0 rhel-8-for-x86_64-nfv-rpms kernel-rt-debug.x86_64 4.18.0-80.7.1.rt9.153.el8_0 rhel-8-for-x86_64-nfv-rpms kernel-rt-debug-devel.x86_64 4.18.0-80.7.1.rt9.153.el8_0 rhel-8-for-x86_64-nfv-rpms kernel-rt-debug-kvm.x86_64 4.18.0-80.7.1.rt9.153.el8_0 rhel-8-for-x86_64-nfv-rpms kernel-rt-devel.x86_64 4.18.0-80.7.1.rt9.153.el8_0 rhel-8-for-x86_64-nfv-rpms kernel-rt-doc.noarch 4.18.0-80.7.1.rt9.153.el8_0 rhel-8-for-x86_64-nfv-rpms kernel-rt-kvm.x86_64 4.18.0-80.7.1.rt9.153.el8_0 rhel-8-for-x86_64-nfv-rpms [ output omitted...]
(undercloud)USD sudo dnf install libguestfs-tools
sudo systemctl disable --now iscsid.socket
(undercloud)USD tar -xf /usr/share/rhosp-director-images/overcloud-full.tar (undercloud)USD tar -xf /usr/share/rhosp-director-images/ironic-python-agent.tar
(undercloud)USD cp overcloud-full.qcow2 overcloud-realtime-compute.qcow2
(undercloud)USD virt-customize -a overcloud-realtime-compute.qcow2 --run-command 'subscription-manager register --username=<username> --password=<password>' [ 0.0] Examining the guest [ 10.0] Setting a random seed [ 10.0] Running: subscription-manager register --username=<username> --password=<password> [ 24.0] Finishing off
sudo subscription-manager list
(undercloud)USD virt-customize -a overcloud-realtime-compute.qcow2 --run-command 'subscription-manager attach --pool [subscription-pool]'
(undercloud)USD cat rt.sh #!/bin/bash set -eux subscription-manager repos --enable=[REPO_ID] dnf -v -y --setopt=protected_packages= erase kernel.USD(uname -m) dnf -v -y install kernel-rt kernel-rt-kvm tuned-profiles-nfv-host # END OF SCRIPT
(undercloud)USD virt-customize -a overcloud-realtime-compute.qcow2 -v --run rt.sh 2>&1 | tee virt-customize.log
(undercloud)USD virt-customize -a overcloud-realtime-compute.qcow2 --selinux-relabel
(undercloud)USD mkdir image (undercloud)USD guestmount -a overcloud-realtime-compute.qcow2 -i --ro image (undercloud)USD cp image/boot/vmlinuz-4.18.0-80.7.1.rt9.153.el8_0.x86_64 ./overcloud-realtime-compute.vmlinuz (undercloud)USD cp image/boot/initramfs-4.18.0-80.7.1.rt9.153.el8_0.x86_64.img ./overcloud-realtime-compute.initrd (undercloud)USD guestunmount image
(undercloud)USD openstack overcloud image upload --update-existing --os-image-name overcloud-realtime-compute.qcow2
cp /usr/share/openstack-tripleo-heat-templates/environments/compute-real-time-example.yaml /home/stack/templates/compute-real-time.yaml
openstack overcloud roles generate -o /home/stack/templates/rt_roles_data.yaml Controller Compute ComputeRealTime
- name: ComputeRealTime description: | Compute role that is optimized for real-time behaviour. When using this role it is mandatory that an overcloud-realtime-compute image is available and the role specific parameters IsolCpusList, NovaComputeCpuDedicatedSet and NovaComputeCpuSharedSet are set accordingly to the hardware of the real-time compute nodes. CountDefault: 1 networks: InternalApi: subnet: internal_api_subnet Tenant: subnet: tenant_subnet Storage: subnet: storage_subnet HostnameFormatDefault: '%stackname%-computerealtime-%index%' ImageDefault: overcloud-realtime-compute RoleParametersDefault: TunedProfileName: "realtime-virtual-host" KernelArgs: "" # these must be set in an environment file IsolCpusList: "" # or similar according to the hardware NovaComputeCpuDedicatedSet: "" # of real-time nodes NovaComputeCpuSharedSet: "" # NovaLibvirtMemStatsPeriodSeconds: 0 ServicesDefault: - OS::TripleO::Services::Aide - OS::TripleO::Services::AuditD - OS::TripleO::Services::BootParams - OS::TripleO::Services::CACerts - OS::TripleO::Services::CephClient - OS::TripleO::Services::CephExternal - OS::TripleO::Services::CertmongerUser - OS::TripleO::Services::Collectd - OS::TripleO::Services::ComputeCeilometerAgent - OS::TripleO::Services::ComputeNeutronCorePlugin - OS::TripleO::Services::ComputeNeutronL3Agent - OS::TripleO::Services::ComputeNeutronMetadataAgent - OS::TripleO::Services::ComputeNeutronOvsAgent - OS::TripleO::Services::Docker - OS::TripleO::Services::Fluentd - OS::TripleO::Services::IpaClient - OS::TripleO::Services::Ipsec - OS::TripleO::Services::Iscsid - OS::TripleO::Services::Kernel - OS::TripleO::Services::LoginDefs - OS::TripleO::Services::MetricsQdr - OS::TripleO::Services::MySQLClient - OS::TripleO::Services::NeutronBgpVpnBagpipe - OS::TripleO::Services::NeutronLinuxbridgeAgent - OS::TripleO::Services::NeutronVppAgent - OS::TripleO::Services::NovaCompute - OS::TripleO::Services::NovaLibvirt - OS::TripleO::Services::NovaLibvirtGuests - OS::TripleO::Services::NovaMigrationTarget - OS::TripleO::Services::ContainersLogrotateCrond - OS::TripleO::Services::OpenDaylightOvs - OS::TripleO::Services::Podman - OS::TripleO::Services::Rhsm - OS::TripleO::Services::RsyslogSidecar - OS::TripleO::Services::Securetty - OS::TripleO::Services::SensuClient - OS::TripleO::Services::SkydiveAgent - OS::TripleO::Services::Snmp - OS::TripleO::Services::Sshd - OS::TripleO::Services::Timesync - OS::TripleO::Services::Timezone - OS::TripleO::Services::TripleoFirewall - OS::TripleO::Services::TripleoPackages - OS::TripleO::Services::Vpp - OS::TripleO::Services::OVNController - OS::TripleO::Services::OVNMetadataAgent
source ~/stackrc openstack flavor create --id auto --ram 6144 --disk 40 --vcpus 4 compute-realtime openstack flavor set --property "cpu_arch"="x86_64" --property "capabilities:boot_option"="local" --property "capabilities:profile"="compute-realtime" compute-realtime
openstack baremetal node set --property capabilities='profile:compute-realtime,boot_option:local' <node_uuid>
parameter_defaults: OvercloudComputeRealTimeFlavor: compute-realtime
(undercloud)USD openstack overcloud deploy --templates -e [your environment files] -r /home/stack/templates/rt~/my_roles_data.yaml -e home/stack/templates/compute-real-time.yaml
parameter_defaults: ComputeRealTimeParameters: IsolCpusList: "1" NovaComputeCpuDedicatedSet: "1" NovaComputeCpuSharedSet: "0" KernelArgs: "default_hugepagesz=1G hugepagesz=1G hugepages=16" NovaComputeDisableIrqBalance: true
openstack overcloud roles generate -o ~/rt_roles_data.yaml Controller ComputeRealTime
(undercloud)USD openstack overcloud deploy --templates -r /home/stack/rt_roles_data.yaml -e [your environment files] -e /home/stack/templates/compute-real-time.yaml
uname -a Linux overcloud-computerealtime-0 4.18.0-80.7.1.rt9.153.el8_0.x86_64 #1 SMP PREEMPT RT Wed Dec 13 13:37:53 UTC 2017 x86_64 x86_64 x86_64 GNU/Linux cat /proc/cmdline BOOT_IMAGE=/boot/vmlinuz-4.18.0-80.7.1.rt9.153.el8_0.x86_64 root=UUID=45ae42d0-58e7-44fe-b5b1-993fe97b760f ro console=tty0 crashkernel=auto console=ttyS0,115200 default_hugepagesz= 1G hugepagesz= 1G hugepages= 16 tuned-adm active Current active profile: realtime-virtual-host grep ^isolated_cores /etc/tuned/realtime-virtual-host-variables.conf isolated_cores=1 cat /usr/lib/tuned/realtime-virtual-host/lapic_timer_adv_ns 4000 # The returned value must not be 0 cat /sys/module/kvm/parameters/lapic_timer_advance_ns 4000 # The returned value must not be 0 To validate hugepages at a host level: cat /proc/meminfo | grep -E HugePages_Total|Hugepagesize HugePages_Total: 64 Hugepagesize: 1048576 kB To validate hugepages on a per NUMA level (below example is a two NUMA compute host): cat /sys/devices/system/node/node0/hugepages/hugepages-1048576kB/nr_hugepages 32 cat /sys/devices/system/node/node1/hugepages/hugepages-1048576kB/nr_hugepages 32 crudini --get /var/lib/config-data/puppet-generated/nova_libvirt/etc/nova/nova.conf compute cpu_dedicated_set 1 crudini --get /var/lib/config-data/puppet-generated/nova_libvirt/etc/nova/nova.conf compute cpu_shared_set 0 systemctl status irqbalance ● irqbalance.service - irqbalance daemon Loaded: loaded (/usr/lib/systemd/system/irqbalance.service; enabled; vendor preset: enabled) Active: inactive (dead) since Tue 2021-03-30 13:36:31 UTC; 2s ago
openstack server create --image <rhel> --flavor r1.small --nic net-id=<dpdk_net> test-rt
virsh dumpxml <instance_id> | grep vcpu -A1 <vcpu placement='static'>4</vcpu> <cputune> <vcpupin vcpu='0' cpuset='1'/> <vcpupin vcpu='1' cpuset='3'/> <vcpupin vcpu='2' cpuset='5'/> <vcpupin vcpu='3' cpuset='7'/> <emulatorpin cpuset='0-1'/> <vcpusched vcpus='2-3' scheduler='fifo' priority='1'/> </cputune>
openstack flavor set --property hw:cpu_policy=dedicated 99