KVM Notes
Summary
This document contains useful notes from user experience.
Notes
Choosing hardware
When selecting hardware check if it really supports virtualization as that is required for KVM to work. Double check corresponding settings in BIOS, if it is enabled, if it still does not work - check weather motherboard BIOS upgrade is available.
list of CPUs supporting virtualization: Wikipedia about virtualization support on x86 CPUs
In short: If buying Intel CPU double-check if you are getting correct model, if AMD, all new CPUs will support virtualization.
KVM guest multi CPU
When using RouterOS os primary OS on the router changing /system hardware settings will change kernel that is loaded at boot time effectively enabling or disabling SMP support in RouterOS. But using this setting in KVM guest does not work as intended, because in KVM guest configuration user can explicitly point what kernel to use, default setting is kernel="/boot/vmlinuz" that loads guest with non-SMP kernel.
Correct setting for multi CPU support is kernel="/boot/vmlinuz-smp"
Performance considerations
When planning using KVM guests, consider that host system will have to handle all the packets that are passing through, so still, host systems packets per second is important.
Packet flow
from one RouterOS KVM guest to another packets will always go through RouterOS host system.