Tips for Tuning and Optimizing RHEL Virtualization Hosts

To get the best possible performance from virtual machines running on Red Hat Enterprise Linux KVM host systems (whether using separate hosts or hosts in a RHEV environment), there are some steps you can take to tune and optimize your systems. Some tuning techniques can be applied to the KVM host, while others can directly tune your virtual machines.

The RHEL 6 Virtualization Tuning and Optimization Guide offers tips on tuning your RHEL KVM hosts and the virtual machines that run on them. Here are some examples of tuning and optimization techniques that you can find in this guide.

Host Tuning

• Host tuning with tuned: On a KVM host, you can set the tuned profile to virtual-host. This results in changes to system settings (such as decreased swapiness and more aggressive dirty page writebacks) that can improve the host performance.

• Network Tuning Tips: Configuring dedicated networks and setting appropriate MTU values can improve performance of your KVM host.

• Huge Pages and Transparent Huge Pages: Enabling huge page memory support on RHEL hosts can significantly improve system performance for large-memory and memory-intensive workloads.

• NUMA vCPU Pinning: Assigning specific CPUs and memory to virtual machines using NUMA settings can help you make the most efficient use of your host system's memory.

Virtual Machine Tuning

Tuning that is aimed at a specific virtual machine can be accomplished by changing settings associated with how the virtual machine is launched or by changing settings with the virtual machine itself. Here are some examples:

• Operating System Details and Devices: If you use the virt-manager tool (Virtual Machine Manager window) to create a new virtual machine on a RHEL KVM host, simply selecting the right operating system type or removing unused drivers as described in this manual can improve performance of that virtual machine.

• CPU Performance Options: Again, when you first configure your virtual machine using virt-manager, things such as overcommitting virtual CPUs can negatively impact performance, while choosing the right CPU configuration can have a positive impact in the VM's performance.

• Virtual machine tuning with tuned: On a virtual machine, you can set the tuned profile to virtual-guest. This results in changes to system settings (such as decreased swapiness in virtual memory) that can improve the performance of that virtual machine.

• Virtio drivers on virtual machines: Using virtio drivers improves network performance for virtual machines by reducing copy operations and lowering latency.