Description of problem: The "Configuring RealTime Compute" section of the OpenStack manual lacks customizations to the guest device configuration necessary for realtime operation. Version-Release number of selected component (if applicable): OSP 13 is affected: https://access.redhat.com/documentation/en-us/red_hat_openstack_platform/13/html/advanced_overcloud_customization/realtime-compute#rtc-instances Newer versions seem to be affected as well. How reproducible: Easily. Steps to Reproduce: 1. Enable graphics or USB and run cyclictest. 2. Perform graphics operations with Cirrus and VNC. Actual results: Cirrus and VNC (and X11 in zoom mode): # Total: 000026758 # Min Latencies: 00005 # Avg Latencies: 00006 # Max Latencies: 04122 USB and usbtablet: # Total: 000003784 # Min Latencies: 00005 # Avg Latencies: 00006 # Max Latencies: 00259 Expected results: no USB and no graphics: # Min Latencies: 00005 # Avg Latencies: 00006 # Max Latencies: 00014 Additional info: The manual should be updated with the following information: Its recommended to disable USB and graphics since the execution of these features can negatively impact realtime workloads. 1. Edit the guest XML configuration file virsh edit guestname 2. Make the following changes: Remove non-essential hardware, such as USB devices, serial devices, QXL device, the graphic display, etc libvirt adds a default USB controller to the xml schema, change its model to none to disable it, eg: <controller type='usb' index='0' model='none'/>
This is less a documentation and more an issue with nova. If these features should be disabled for real-time, nova should expose the knobs to do this or do it automatically. One should not modify libvirt's XML behind nova's back. I'm going to close this as WONTFIX. Can you please reopen an RFE against nova where we can track this work?