Tobias Hunger wrote:

Both. Assuming that context switching is an expensive operation, and that most of the cost comes from flushing the TLBs, the current model has more overhead than a model where the drivers are mapped into the same address space (though still protected from domU access other that through hypercalls) as the currently running domain. Xen already contains magic that allows it to be permanently mapped into running domains, while still being protected from accidential/malicious access.

I am calling that monolithic, because that is what standard linux does, and what the old Xen 1.x did. The current model is more like a microkernel, such as L4 or Mach (though of course a lot more clever, no offense people ;-))

Apart from perhaps increasing performance, I was saying it would be cool if the Xen-interface could be provided on platforms such as Windows or native Linux. People have done similar stuff before (e.g. VMWare vmmon, the Adeos nanokernel, coLinux), so it should be possible. It seems Xen would have better chances of world domination that way, if that is a goal. It would also save some duplication of effort in porting guestOSes to the different models out there.

Anyway, it was just an idea, and it is likely that with future hardware the Xen NGIO/microkernel model will finally be overhead-free, vendors will start writing Xen-VM drivers, and we will all live happily ever after :-).

Jacob