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Re: [Xen-users] Multiseat workstation with one VM per user

On 2014-12-31 12:38, Luis P. Mendes wrote:

- base system (dom0) as lean as possible, just for Xen

Trying to lean things out to a great extent is generally a
waste of time. On any recent Linux distribution the base
install is sufficiently large that it's losing game and
saving a few GB of disk space is not worth the effort.

- one Slackware VM and one Ubuntu VM with direct access to hardware
via PV

You need to clarify what exactly you mean by this. Getting
hardware passthrough working at all can be hit and miss and
is very hardware dependant. There are so many hardware and
firmware bugs around that luck is a large factor in hardware

- other VMs for occasional use, which can run in virtualized hardware.

- three fanless graphic cards, for example AMD Radeon 6450. One for
base system (could be a cheaper one), and one dedicated (passthrough)
to Slackware VM, and similar for the third one for the Ubuntu VM.
Iâd be using HDMI as the output interface for the two VMs and VGA
for the base system, in case of necessity.

 I've read http://wiki.xen.org/wiki/Xen_VGA_Passthrough [1] and
http://wiki.xen.org/wiki/Xen_VGA_Passthrough_Tested_Adapters [2]

but still would like your opinions, as itâs my first time with Xen
and Iâm not fully aware of all the corners I could face.

People's experience with ATI cards is at best mixed. I never got
it fully working. Most people find it works OK on the first boot
of the VMs, but as soon as you need to reboot VMs things fall
apart pretty quickly with cards not being reinitialized properly
on a reboot. That's on Windows VMs. With Linux VMs, a lot would
depent on how up to the job the radeon driver is. Last I checked,
it wasn't.

If all you are after is Linux-on-Linux kind of a setup, you would
probably be a lot better off with something like LXC, OpenVZ or
VServer for separating server tasks.

If all you need is a multi-seat workstation, you don't need
virtualization at all, you can just configure multiple Xorg
instances to access different GPU/keyboard/mouse sets.

Now, what Iâd like to know:

1. Is Slackware 14.1 or current with the xen package from
http://slackbuilds.org/repository/14.1/system/xen/ [3] as stable as
Slackware without it? Iâve been using Slackware for ten years as a
rock solid Linux. Would I gain anything in having another OS as dom0?
Is NetBSD up to the task?

I think this is the first time I heard of anyone using Slackware in
at least 10 years. Most people these days prefer to have a
package management system in their OS.

Does NetBSD even have support for being Xen dom0?

2. As a multiseat workstation, Iâd have to configure Xorg to use a
keyboard, a mouse and a screen with a graphic device? As Iâd like to
have native performance for each of the two VMs, how should I
configure Xorg? How can each of us have the same keyboard, mouse,
graphic card and monitor with native graphics speed attached to each
VM all the time?

See above.

3. What PCIe slots do I need for the fanless graphic cards? 16X? 4X?
Or 1x is sufficient not to be constrained and use full power of such
fanless cards? I could use at least one for GPU programming in order
to speed up data treatment in the future.

Results for this will vary massively based on the application.
Google for GPU benchmarks with differet PCIe lane widths.

In most cases you will end up having problems getting the card to
fit in the smaller slot. You will at least need to cut open the
end of the slot, and on most motherboards there will be components
on the board that will get in the way of the card's PCIe connector.

4. Iâd like to have dedicated disk partitions for each VM. I think
there should be no problem about this, am I correct?

Not a problem.

5. Can I dedicate CPU cores to each VM?


6. Iâve read that itâs more stable to passthrough usb devices
individually, than usb host controllers. Is this still the case? As
Iâd like each of the two of us to have two USB 3.0 ports in

Passing USB devices has been hit and miss for me. Passing PCIe devices
that are USB host controllers, on the other hand, has worked well.

7. (repetition)  Is NetBSD with its lower power requirements up to
this task?

There is no gain. Getting this kind of a setup to work reliably at
all on OS-es that are used (and thus debugged) by thousands of people
is difficult enough without getting bogged down in OS-es that only
a handful of people use in a similar scenario.

In conclusion:

One workstation, with native disk and graphic card access to each of
the two main VMs running as fast as it they were native.

As fast as native? Not going to happen. Fast enough? Sure. I have
a triple seat gaming machine that works quite well, but that is
very different from what you are proposing above (Nvidia GPUs,
Windows guests)

What else would you advise me?

You need to establish whether you need different VMs in the
first place or whether you would be better off with a combination
of containers and multi-seat Xorg configuration.


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