Xen users - Apr 2009 - Increasing network performance on Windows DomUs

Hi all,

I''m preparing to deploy some Windows servers under Xen on Red Hat 5  
and would like to maximize network performance.  I''ve been looking  
over some previous posts and it looks like the present situation is  
this, and please do correct me if I''m wrong:

- Windows guests get slower network performance than their Dom0''s  
because of the fully-virtualized hardware (HVM)
- Assigning the Dom0 and DomU its own processor core can improve this  
slightly
- It''s possible to use Windows paravirtual (PV) drivers from  
XenExpress or other commercial products, but they will only work with  
commercial versions of Xen and not open-source ones such as Red Hat''s  
version

If the last point is true, what options are there?  If I have a Dom0  
machine with lots of NICs, can I assign one of the NICs to my DomU and  
bypass the whole HVM, network bridge, etc?  At this point, I''m only  
interested in getting one of the windows guests with optimal network  
speed.  For now, I can deal with less-than-optical network performance  
on my other windows guests, but it would be nice to know all the  
options.

Here are some details about my environment:

Dom0 = IBM 3550, Dual-core 3.0 Ghz Xeon
DomU = 2 paravirtual linux guests. 1 fully-virtual Windows 2008 Server

Right now, an iperf test to a server on the same subnet yields 850 Mb/ 
s from either Dom0 or one of the linux DomUs, but only about 30 Mb/s  
from the Windows DomU.

Any ideas will be greatly appreciated, and I''m happy to share the  
results.

thanks,

...adam






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On Thu, Apr 30, 2009 at 1:08 PM, Adam Wead <awead@indiana.edu>
wrote:
> Hi all,
>
> I''m preparing to deploy some Windows servers under Xen on Red Hat
5 and
> would like to maximize network performance.  I''ve been looking
over some
> previous posts and it looks like the present situation is this, and please
> do correct me if I''m wrong:
>
> - Windows guests get slower network performance than their Dom0''s
because of
> the fully-virtualized hardware (HVM)
nitpicking:

- HVM isn''t "fully-virtualized hardware", it''s the
hardware support
(on the CPU) for virtualization.  before that was available, it was
possible to do fully virtualized hardware (qemu is an example); but it
was too slow.  HVM lets you have a full set of priviledge rings in a
VM, making it far faster than software emulation.

- HVM is slower than PV, because the new context switches are slower
than usual context switches when crossing rings, and the software is
more complex, but it''s not the biggest bottleneck that concerns you.

- out-of-the-box systems (usually windows) do run, thanks not only to
HVM, but also thanks to a modified qemu process running on Dom0, that
receives all the hardware access of an HVM DomU, and does all the
device emulation.  this emulation is totally done in software, so it''s
not as fast as one would wish.

- qemu emulated hardware is (on purpose) very generic and a little
old, usually IDE drives, and simple network cards.  that makes it easy
to support a wide variety of systems, but also means that the drivers
used by the guest OS have to do a lot of bit-twiddling to make it
work.  each of these small accesses means a full context switch,
limiting performance.

- PV drivers help (a lot!) both because the corresponding Dom0
software is far simpler than emulating every detail of a hardware
card; but also because there are a lot less context switches per
transfer, and also it''s easier to make a single hypercall manage a
bigger chunk of data than what old emulated chips can handle.


now, to your real question...

commercial PV drivers are somewhat expensive, and usually locked to
very specific Xen versions; but there''s a version of Open Source
drivers, called "GPLPV drivers", thanks to James Harper, a common
contributor to this list.  they''re not perfect, but several users can
report that they work reliably and efficiently.



-- 
Javier

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On Fri, May 1, 2009 at 1:08 AM, Adam Wead <awead@indiana.edu>
wrote:
> - It''s possible to use Windows paravirtual (PV) drivers from
XenExpress or
> other commercial products, but they will only work with commercial versions
> of Xen and not open-source ones such as Red Hat''s version
>
> If the last point is true, what options are there?
Try gplpv :
- http://wiki.xensource.com/xenwiki/XenWindowsGplPv/Installing (a
little out of date)
- http://lists.xensource.com/archives/html/xen-users/2009-04/msg00058.html
- http://meadowcourt.org/downloads/

The other option is using stubdom (http://wiki.xensource.com/xenwiki/StubDom)

Regards,

Fajar

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On Tue, May 5, 2009 at 8:13 AM, Adam Wead <awead@indiana.edu>
wrote:
> Thanks, Fajar, and thanks to Javier for the posts to this thread.
>
> I was able to install gplpv_chk_wlh_AMD64_0.10.0.55.msi on a new install of
> Windows Server 2008 Enterprise, and the network speed did increase.
>  Previously, with the old drivers, iperf tests reported about 40 Mb/s, now
> with the GplPv drivers it''s about 140 Mb/s, and the NIC on the
guest
> actually says it''s running at gigabit speed.  Not bad.
Ehm, you didn''t say that you''re running Windows 2008 x64. BE
CAREFUL.

When not installed correctly, it can cause disk corruption.
Please check :
- how many disks you have now? If previously you have one (c:) but now
suddenly you have two (c: and d:) wit the same content, then most
likely your disk is corrupted already
- open device manager. Which NIC is active? Is it Realtek, or is it the Xen Net?
>From my experience I had to do some specific setup (not simply click
"Next" and reboot) to get it working correctly.
If you had it working correctly, great! Just to be safe though, you
should check the above.
>
> The Shutdown Monitor also installed automagically, and now the guest
> restarts gracefully...  Thank you, James Harper!
>
> Now, if I can only figure out how to sign the driver so I don''t
have to go
> through that annoying process of disabling driver signature enforcement.
>  I''d love to hear anyone''s experiences with that.  It
seems all I need is
> the signtool on Windows, but I can''t figure out how to actually
get that.
>
> Any suggestions are appreciated.
Again, from experience, testsigning doesn''t work correctly with GPLPV.
Or rather, disk driver works but NIC driver doesn''t. I suggest you use
Ready Driver Plus (try Google for it). Basically it automate some key
press to select "disable driver signing enforcement" on every boot.

Regards,

Fajar

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On May 4, 2009, at 11:33 PM, Fajar A. Nugraha wrote:
> On Tue, May 5, 2009 at 8:13 AM, Adam Wead <awead@indiana.edu> wrote:
>> Thanks, Fajar, and thanks to Javier for the posts to this thread.
>>
>> I was able to install gplpv_chk_wlh_AMD64_0.10.0.55.msi on a new  
>> install of
>> Windows Server 2008 Enterprise, and the network speed did increase.
>>  Previously, with the old drivers, iperf tests reported about 40  
>> Mb/s, now
>> with the GplPv drivers it''s about 140 Mb/s, and the NIC on the
guest
>> actually says it''s running at gigabit speed.  Not bad.
>
> Ehm, you didn''t say that you''re running Windows 2008 x64.
BE CAREFUL.
>
> When not installed correctly, it can cause disk corruption.
> Please check :
> - how many disks you have now? If previously you have one (c:) but now
> suddenly you have two (c: and d:) wit the same content, then most
> likely your disk is corrupted already
No, I''m still at one disk.
> - open device manager. Which NIC is active? Is it Realtek, or is it  
> the Xen Net?
When I first installed the GplPV drivers, both the Realtek and the  
Xen Net Device driver were active, the latter appearing as Local Area  
Connection 2.  I disabled the Realtek connection and activated the  
Xen driver.  All seems well after a couple of reboots.  I could go  
ahead and remove the Realtek driver completely, but maybe it''s a good  
idea to keep it around in case the other goes haywire?
>
> From my experience I had to do some specific setup (not simply click
> "Next" and reboot) to get it working correctly.
> If you had it working correctly, great! Just to be safe though, you
> should check the above.
Thanks for the caveat.  Other than the disabling/enabling of the  
drivers, it was pretty simple, but I will keep an eye on it.
>
>>
>> The Shutdown Monitor also installed automagically, and now the guest
>> restarts gracefully...  Thank you, James Harper!
>>
>> Now, if I can only figure out how to sign the driver so I
don''t
>> have to go
>> through that annoying process of disabling driver signature  
>> enforcement.
>>  I''d love to hear anyone''s experiences with that.  It
seems all I
>> need is
>> the signtool on Windows, but I can''t figure out how to
actually
>> get that.
>>
>> Any suggestions are appreciated.
>
> Again, from experience, testsigning doesn''t work correctly with
GPLPV.
> Or rather, disk driver works but NIC driver doesn''t. I suggest you
use
> Ready Driver Plus (try Google for it). Basically it automate some key
> press to select "disable driver signing enforcement" on every
boot.
Great.  Testsigning looks to be a pain anyway.  I''ll give that a try.

Thanks again for the help.  It''s very appreciated!

best,

...adam



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