[SGVLUG] Xen

[John Kreznar]

In a message purporting to be from matti <mathew_2000 at yahoo.com> but
lacking a digital signature, it is written:

> I am still looking to see which MB/chipset would support Xen, and
> attempting to find a list of chipsets which work with this.

The most useful and authoritative answers to this that I found when I
chose hardware for xen last year were [1,2].

Also, USENET newwsgroup gmane.comp.emulators.xen.user is valuable.  I
archive it all, and that's one place I search when I've got a question.

An important distinction to keep in mind is whether an unmodified
operating system can be run (full virtualization, requiring hardware
support), or an operating system tailored for Xen has to be used
(paravirtualization).  There's nothing wrong with paravirtual, but
sometimes you want to run a system not having the paravirtual hooks.  I
ran Linux paravirtual for years on an AMD Athlon.

The second important distinction, assuming you have hardware to run full
virtual, is whether the hardware supports IOMMU [3,4].  When I chose
hardware for xen in early 2010, AMD was not yet delivering a product
with IOMMU.  Intel VT-d technology was the only game in town.  I chose a
Supermicro 5036T [3], which uses a X8SAX motherboard with an Intel VT-d
CPU.

With IOMMU, peripheral devices can be selectively "passed through" the
xen hypervisor to a virtual machine.  IO memory (such as DMA) is then
mapped by the hardware just like CPU-addressed memory, so the virtual
machine can efficiently use the device as though it were directly
connected.  I use this for sound and to pass through a subset of the USB
ports.

[1] http://wiki.xensource.com/xenwiki/HVM_Compatible_Processors
[2] http://wiki.xensource.com/xenwiki/HVM_Compatible_Motherboards
[3] http://en.wikipedia.org/wiki/X86_virtualization
[4] http://wiki.xensource.com/xenwiki/VTdHowTo

-- 
 John E. Kreznar jek at ininx.com 9F1148454619A5F08550 705961A47CC541AFEF13

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