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RE: [Xen-devel] Questioning the Xen Design of the VMM

To: Al Boldi <a1426z@xxxxxxxxx>, Petersson@xxxxxxxxxxxxxx, Mats <Mats.Petersson@xxxxxxx>
Subject: RE: [Xen-devel] Questioning the Xen Design of the VMM
From: Daniel Stodden <stodden@xxxxxxxxxx>
Date: Thu, 10 Aug 2006 20:07:48 +0200
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On Thu, 2006-08-10 at 18:34 +0200, Petersson, Mats wrote:

> Context-switching is only part of the problem, as Daniel says. 

> IOMMU is a technology that is coming in future products from AMD

>  (and I'm sure Intel are working on such products as well. 

> IBM already have a chipset in production for some of the PowerPC 

> and x86-based servers).

i didn't have a look yet at the papers from amd, but
it may be of interest that the PCI interfaces (1998, maybe even earlier)
built by sun for their ultrasparc processors already implemented such a
beast. al, docs on the bridge should be available from sun online, if
you're interested in such things.

the basic idea being virtualization of the I/O address space, this
feature is quite cool even if you don't give a single thought about
system virtualization (sun probably didn't at that point). getting your
hands on contiguous, dma-able memory areas can be a permanent headache
in os and device driver design if you peripheral bus seeks physical
memory untranslated. put a translation table in between and upstream
transactions become a non-issue, without offloading any additional logic
into the peripheral bus interface.

mats, i suppose amd's iommu solves this as well?


Daniel Stodden
LRR     -      Lehrstuhl für Rechnertechnik und Rechnerorganisation
Institut für Informatik der TU München             D-85748 Garching
http://www.lrr.in.tum.de/~stodden         mailto:stodden@xxxxxxxxxx
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