QEMU/KVM are a popular backend for OpenStack. In StarlingX Openstack (stx-openstack) this is also the case. I’ll try to describe various techniques that I used to optimize RT behavior on an STX 4.0.1 cluster with worker nodes.


Bare-Metal is a a physical computer and it’s base OS

Host is a bare-metal machine that runs VMs

Thread is a core of a CPU

CPU thread refers to the thread on the host system CPU

vCPU thread is a thread on a VM’s virtualized CPU

Note: I borrowed terminology heavily from this article on null-src

Isolating CPUs

My last article covers this topic. Isolating a VM’s vCPU threads from the host system ensures that host’s processes don’t interfere with the VM.

Scheduling Openstack VMs on isolated cores

CPU Affinity

using taskset

Linux Process Scheduler Tuning

GRUB cmdline

Okay… don’t delete the console entries in your command line… the entries below are for isolated cpu 1. This is not a comprehensive list… Just append whatever makes sense to you.

GRUB_CMDLINE_LINUX_DEFAULT="threadirqs rcu_nocbs=1 rcu_nocb_poll isolcpus=1 nohz_full=1 nohz=off intel_pstate=disable nosoftlockup nohalt"