KVM as hypervisor choice in GCE

Question

As per wikipedia, google compute engine uses KVM as hypervisor. I can see mention about vcpu while creating an instance.

Why KVM? Why not VMware OR Xen? I mean what is the specific reason to choose KVM as a Hypervisor choice?

PS: Even Xen is a Open source product.

Answer 1

There were a number of factors in the decision, you might not be surprised to learn. :-)

One important factor was compatibility between KVM and existing isolation/scaling processes at Google. (cgroups aka "containers") This allows Google to reuse the same mechanisms that it uses to ensure performance of applications like websearch and gmail to provide consistent performance between VMs scheduled on the machine. This helps GCE avoid noisy neighbor problems.

As you're probably aware, Google has had a long history of Linux kernel development; using KVM allows Google to leverage that talent for GCE. In addition, the hypervisor/hardware emulation split in KVM (where the hypervisor implemented by KVM only emulates a few low-level devices/features, and defers the remaining emulation the the process that opens /dev/kvm) allows for development of virtual devices that have access to the full range of user-space software, including infrastructure like Colossus and BigTable where needed.

Xen, VMware, and HyperV are also great hypervisors and machine emulators, but hopefully that gives you a glimpse into some of the reasons that KVM was a good fit for Google.