We always wanted the libguestfs appliance to boot in 5 seconds, and today after about a week of tweaking and optimization, we made that happen. On relatively old hardware too …
real 0m4.954s user 0m2.117s sys 0m1.739s
The patches are not upstream yet, but we hope to have the required changes in Fedora 14 by the time it comes out.
Another optimization that we made was to switch to using virtio-serial for communications. This is considerably faster than the current qemu user-net-based communication channel.