[shortsunblack]

KVM was made because Citrix made moves against Xen that spooked Linux community, hence KVM. Then Red Hat ran with it and based its virtualization platform on it.

Citrix involvement has subsided in meantime and the ecosystem is much healthier (governance is actually under Linux Foundation), but the damage was done.

Xen to this day lacks in features, also.

[jacobgorm]

Also, Xen's main clame to fame was that para-virtualization allowed it to host Linux and *BSD VMs at close to zero overhead, but at time what everyone was looking for was a way to host Windows VMs, which is where all the pain points and the money was. CPUs were evolving to support this use-case, making para-virtualization less important, and Xen had to evolve quite quickly to include QEMU in the mix, leaving a bit of convoluted mess initially, and causing a lot of friction during the attempts to get merged into the Linux kernel. On top, the Xen management tool-stack had been written by happy amateurs in Python and Twisted, before any of those technologies where near ready for production use, with massive slowness and unfixable memory leaks as results. KVM provided a fresh take built with the benefits of hindsight, got merged into Linux on the first attempt, and gained the backing of Redhat, and the rest is more of less history.

[jacobgorm]

KVM was launched before Citrix acquired XenSource. But Redhat had also tried to acquire XenSource and threatened its founders that if they did not come along Redhat would “rip off their heads and shit down the hole”, because “Redhat was the only company allowed to make money off open source”. In that light it made sense for Redhat to back a competitor to Xen.