第10章 Configuring Real-Time Compute
In some use-cases, 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
ComputeRealTimerole 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.
10.1. Preparing Your Compute Nodes for Real-Time
Real-time Compute nodes are supported only with Red Hat Enterprise Linux version 7.5 or later.
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 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 must enable the
rhel-7-server-nfv-rpmsrepository for RT-KVM to build the real-time image.注記You need a separate subscription to Red Hat OpenStack Platform for Real Time before you can access this repository. For details on managing repositories and subscriptions for your undercloud, see the Registering and updating your undercloud section in the Director Installation and Usage guide.
To check which packages will be installed from the repository, run the following command:
$ yum repo-pkgs rhel-7-server-nfv-rpms list Loaded plugins: product-id, search-disabled-repos, subscription-manager Available Packages kernel-rt.x86_64 3.10.0-693.21.1.rt56.639.el7 rhel-7-server-nfv-rpms kernel-rt-debug.x86_64 3.10.0-693.21.1.rt56.639.el7 rhel-7-server-nfv-rpms kernel-rt-debug-devel.x86_64 3.10.0-693.21.1.rt56.639.el7 rhel-7-server-nfv-rpms kernel-rt-debug-kvm.x86_64 3.10.0-693.21.1.rt56.639.el7 rhel-7-server-nfv-rpms kernel-rt-devel.x86_64 3.10.0-693.21.1.rt56.639.el7 rhel-7-server-nfv-rpms kernel-rt-doc.noarch 3.10.0-693.21.1.rt56.639.el7 rhel-7-server-nfv-rpms kernel-rt-kvm.x86_64 3.10.0-693.21.1.rt56.639.el7 rhel-7-server-nfv-rpms [ output omitted…]
Building the real-time image
To build the overcloud image for Real-time Compute nodes:
Install the
libguestfs-toolspackage on the undercloud to get thevirt-customizetool:(undercloud) [stack@undercloud-0 ~]$ sudo yum install libguestfs-tools
重要If you install the
libguestfs-toolspackage on the undercloud, disableiscsid.socketto avoid port conflicts with thetripleo_iscsidservice on the undercloud:$ sudo systemctl disable --now iscsid.socket
Extract the images:
(undercloud) [stack@undercloud-0 ~]$ tar -xf /usr/share/rhosp-director-images/overcloud-full.tar (undercloud) [stack@undercloud-0 ~]$ tar -xf /usr/share/rhosp-director-images/ironic-python-agent.tar
Copy the default image:
(undercloud) [stack@undercloud-0 ~]$ cp overcloud-full.qcow2 overcloud-realtime-compute.qcow2
Register the image and configure the required subscriptions:
(undercloud) [stack@undercloud-0 ~]$ 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
Replace the
usernameandpasswordvalues with your Red Hat customer account details. For general information about building a Real-time overcloud image, see the Modifying the Red Hat Enterprise Linux OpenStack Platform Overcloud Image with virt-customize knowledgebase article.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. For example:
$ sudo subscription-manager list
Attach the Red Hat OpenStack Platform for Real Time subscription to the image:
(undercloud) [stack@undercloud-0 ~]$ virt-customize -a overcloud-realtime-compute.qcow2 --run-command 'subscription-manager attach --pool [subscription-pool]'
Create a script to configure
rton the image:(undercloud) [stack@undercloud-0 ~]$ cat rt.sh #!/bin/bash set -eux subscription-manager repos --enable=rhel-7-server-rpms --enable=rhel-7-server-openstack-13-rpms --enable=rhel-7-server-nfv-rpms yum -v -y --setopt=protected_packages= erase kernel.$(uname -m) yum -v -y install kernel-rt kernel-rt-kvm tuned-profiles-nfv-host # END OF SCRIPT
Run the script to configure the real-time image:
(undercloud) [stack@undercloud-0 ~]$ virt-customize -a overcloud-realtime-compute.qcow2 -v --run rt.sh 2>&1 | tee virt-customize.log
Re-label SELinux:
(undercloud) [stack@undercloud-0 ~]$ virt-customize -a overcloud-realtime-compute.qcow2 --selinux-relabel
Extract
vmlinuzandinitrd:(undercloud) [stack@undercloud-0 ~]$ mkdir image (undercloud) [stack@undercloud-0 ~]$ guestmount -a overcloud-realtime-compute.qcow2 -i --ro image (undercloud) [stack@undercloud-0 ~]$ cp image/boot/vmlinuz-3.10.0-862.rt56.804.el7.x86_64 ./overcloud-realtime-compute.vmlinuz (undercloud) [stack@undercloud-0 ~]$ cp image/boot/initramfs-3.10.0-862.rt56.804.el7.x86_64.img ./overcloud-realtime-compute.initrd (undercloud) [stack@undercloud-0 ~]$ guestunmount image
注記The software version in the
vmlinuzandinitramfsfilenames vary with the kernel version.Upload the image:
(undercloud) [stack@undercloud-0 ~]$ openstack overcloud image upload --update-existing --os-image-name overcloud-realtime-compute.qcow2
You now have a real-time image you can use with the ComputeRealTime composable role on select Compute nodes.
Modifying BIOS settings on Real-time 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.
