Some pci-e resources can be useful to just hand over to VM's directly, like GPU's and infiniband networking cards. This article describes the steps necessary to configure pci-passthrough to hand PCI-devices to certain flavors in the openstack cloud.

Enable IOMMU on the compute-node

Configure Openstack to know about the PCIe-devices.

Configure host-aggregates to aid in the scheduling.

Create a flavor with PCI-e devices attached

Verify that it works