thinking about Haswell desktop

[D. Hugh Redelmeier]

| From: Lennart Sorensen <lsorense-1wCw9BSqJbv44Nm34jS7GywD8/FfD2ys at public.gmane.org>

| On Thu, Sep 05, 2013 at 09:10:44PM -0400, William Park wrote:
| > Asrock?  I don't recommend them.  Horrible RMA experience...
| 
| It isn't a brand I was planning to buy at the moment, but apparently
| they do make VT-d work on their boards unlike most brands.  Strange.

Yeah.  I'm also confused about any relationship between Asus and
ASRock (Pegatron).  Apparently ASUStek spun out Pegatron in 2010.
Afterwards Pegatron still manufactured many Asus boards.

| VT-d allows things like assigning a PCI/PCIe card to a guest.  That is
| the entire card, not part of it, and not a disk.

I remember when XEN was introduced (before VT-D and IOMMU), at an OLS
presentation, XEN folks claimed:
- XEN was a secure way of sharing a machine
- XEN could selectively allocate PCI devices directly to guests

Of course either might be true at one time, but both cannot be true at
one time.  There was no way to give a guest direct access to only a
part of the PCI bus.  But they didn't say that.  A clue to me that the
presentation was too close to marketing.

With VT-d/IOMMU, both could be true at one time.

Giving a guest direct access to a PCI bus device could be a big
performance boost.  Think of any high-bandwidth device.  A NIC or a
disk controller comes to mind.  Without doing any measurements, I
cannot be sure that the performance improvement is significant.

I really want some cards to be willing to provide virtual sub-cards.
The greatest need is in video cards.  Allowing unpriviledged processes
(and VM guests) constrained direct access to parts of a card would
seem to be a big performance win.

To be honest, I don't understand the security model of "direct
rendering" or whatever it is that allows high performance graphics
from userland.  I fear it is insecure.
--
The Toronto Linux Users Group.      Meetings: http://gtalug.org/
TLUG requests: Linux topics, No HTML, wrap text below 80 columns
How to UNSUBSCRIBE: http://gtalug.org/wiki/Mailing_lists