On Fri, Jan 04, 2008 at 11:57:09AM -0500, Dustin Henning wrote:
I was reading an article about Windows PE 2.0 in virtual environments, and apparently Windows PE 2.0 is based on Vista, which doesn't have a driver for the default NIC used by VMWare. The suggested solution is to use a different virtual NIC (a gigabit one). Obviously Xen isn't VMWare, and on top of that, I am not trying to run Windows PE 2.0, or even Vista. However, I had long wondered but never asked this question: Does Xen have any virtual NICs other than the two mentioned in the hvm example files in /etc/xen? More importantly, does it matter, for instance, will Xen or Windows limit the response time or throughput to 100MB/s levels in an hvm environment if a 100MB/s virtual NIC is used? I don't see why it would, but then again, I don't see why SATAII hard drives running on controllers in IDE mode are slowed to IDE speeds, so I wouldn't be surprised if it did, and I am hoping someone can tell me. Thanks, Dustin
Xen HVM guests see _emulated_ hardware. Emulated NIC, Emulated ide/disk controller, etc.
Emulation is slow.
You need to have/install paravirtualized (=optimized) drivers that "bypass" the whole emulation layer and talk directly to Xen.. this way you can get good performance.
Xen includes paravirtualized drivers ("unmodified drivers") for linux HVM guests.
People are working with free/opensource paravirtualized drivers for Windows HVM guests atm, but they're not really usable/stable yet.
XenEnterprise, VirtualIron, and Novell SLES have Windows HVM pv drivers available.. if you buy those products.
-- Pasi
Pasi � wrote:
On Fri, Jan 04, 2008 at 11:57:09AM -0500, Dustin Henning wrote:
I was reading an article about Windows PE 2.0 in virtual environments, and apparently Windows PE 2.0 is based on Vista, which doesn't have a driver for the default NIC used by VMWare. The suggested solution is to use a different virtual NIC (a gigabit one). Obviously Xen isn't VMWare, and on top of that, I am not trying to run Windows PE 2.0, or even Vista. However, I had long wondered but never asked this question: Does Xen have any virtual NICs other than the two mentioned in the hvm example files in /etc/xen? More importantly, does it matter, for instance, will Xen or Windows limit the response time or throughput to 100MB/s levels in an hvm environment if a 100MB/s virtual NIC is used? I don't see why it would, but then again, I don't see why SATAII hard drives running on controllers in IDE mode are slowed to IDE speeds, so I wouldn't be surprised if it did, and I am hoping someone can tell me. Thanks, Dustin
Xen HVM guests see _emulated_ hardware. Emulated NIC, Emulated ide/disk controller, etc.
Emulation is slow.
Compared with hardware, yes. The bit that emulates hardware, yes. Expect the Windows driver to run full speed, it's when there's an interrupt to switch to the emulator that the rot sets in.
I would expect any emulated network device to go as fast as the hardware permits, and not to be constrained to any notion of the emulated device's speed. A real device is constrained by its need to talk to other hardware (electronic signal timing and such) whereas an emulated device is talking to more software.
A more complex device will be harder to emulate and so run slower.
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John Summerfield -
Pasi Kärkkäinen