[Gllug] performance of xen dom0 vs native linux

[Richard Jones]

On Fri, May 08, 2009 at 11:01:31PM +0100, Nahuel Marisi wrote:
> Teh only thing I don't quite get is how the hypervisor controls the hardware
> by using dom0's kernel modules.

Hi, don't top-post please.

The answer is that the hypervisor doesn't use the dom0's kernel
modules.  The dom0 kernel controls most of the hardware (peripherals),
and the hypervisor controls other bits of hardware (CPU, RAM, IO,
interrupts).  The domU's direct their I/O requests to the dom0 which
services them through lots of userspace and dom0 kernel magic, and the
hypervisor is not involved in that part at all (except that it passes
the messages between domains).

So, it's all a bit crazy, but it does work much of the time, except
when you get dreaded errors like 'hotplug scripts not working' where
the inner horribleness is revealed.  The performance story behind Xen
is very nice indeed though.

Rich.

-- 
Richard Jones
Red Hat
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