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Re: [Xen-devel] [Xen VGA Passthrough] Performance of AMD Radeon HD 6450 in Windows 7 HVM domU Poorer Than in Bare-Metal Windows 8.1 OS

  • To: xen-devel@xxxxxxxxxxxxx
  • From: Gordan Bobic <gordan@xxxxxxxxxx>
  • Date: Tue, 09 Sep 2014 19:51:07 +0100
  • Delivery-date: Tue, 09 Sep 2014 18:51:26 +0000
  • List-id: Xen developer discussion <xen-devel.lists.xen.org>

On 2014-09-09 17:51, Teo En Ming wrote:
On 09/09/2014 23:49, Gordan Bobic wrote:

Also, how many VCPUs do you have in the domU vs. total in the

I have 4 VCPUs in the domU and 4 cores in the machine.

A 25-40% drop from virtualization overheads isn't unheard of.
If some parts of the benchmark are CPU bound such a drop
wouldn't be particularly unusual.

Can you test bare metal with CPUs disabled? For example,
if you have a quad core CPU, disable 2 cores, test bare metal.

How do I do that?

See if your BIOS has an option for it. I'm not sure if there
is a way to make Windows itself ignore some cores.

Then start up Xen, limit dom0 to 2 cores, give 2 cores to domU,
test and compare.

4 cores were automatically assigned to dom0. I gave 4 cores to domU as well.

So limit dom0 to 2 cores, and give 2 cores to domU. Ideally pin
dom0 to the first 2 (0,1) and limit domU to the other 2 (2,3).

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