Intel VT hardware acc. does not work with Win XP Guest

[devsk]

Hi,

I am running VB 3.0.12 on a Gentoo box here. I am trying to boot a Windows XP guest with IOAPIC off and Intel VT on but it dies with a Guru Meditation just after it starts to boot off. I have the ACPI HAL installed (device manager->system->update driver->Choose myself->ACPI HAL). The log shows "triple CPU fault..." or something like that.

I can boot with IOAPIC OFF and Intel VT OFF, and the performance is decent. But I want more.

Does anybody know of such issues with 3.0.12. The linux kernerl being used is vanilla 2.6.32-rc7.

Thanks.

[MarkCranness]

I have the ACPI HAL installed (device manager->system->update driver->Choose myself->ACPI HAL). The log shows "triple CPU fault..." or something like that.

That's ambigious. The 'ACPI' selections I see are:

• ACPI Multiprocessor PC (needs IO APIC)
• Advanced Configuration and Power Interface (ACPI) PC (doesn't need IO APIC, but is single processor)

(In XP I don't see ACPI Uniprocessor PC, but that's the same as ACPI Multiprocessor PC anyway.)

Try with IOAPIC ON.
The manual says:

... As with ACPI, the I/O APIC therefore must not be turned off after installation of a Windows guest OS. Turning it on after installation will have no effect however.

AFAIK, the performance hit is not when it's turned on, but when the VM uses it. If the VM has a non multiprocessor HAL, then it won't use it.

[Sasquatch]

I just set 2 CPU's to one of my XP VMs that does not have IO-APIC enabled, and I got this warning:

On the System page, you have assigned more than one virtual CPU to this VM. This will not work unless the IO-APIC feature is also enabled. This will be done automatically when you accept the VM Settings by pressing the OK button.

I run 3.1.0 Beta 2, so the warning might not show up in older versions. This warning just proved that you MUST enable IO-APIC, else it won't work.

[devsk]

I am not using multiple CPUs in guest.

@Mark: You should try "Update Driver" in properties and follow the manual selection in Wizard. Its under Device Manager->Computer (earlier I was typing from memory). Right click and select "Update Driver".

If I enable IOAPIC, the performance is extremely slow. If I disable it, the performance is much much better with ACPI PC HAL but doesn't work with ACPI Multi-Processor HAL. So, I enabled IOAPIC, and then changed HAL to ACPI PC using above procedure, and then moved back to IOAPIC off.

My question was more about Intel VT. If I enable that, I get Guru Meditation.

[Sasquatch]

The manual, or at least here on the forums, mentioned some time ago that VT-x on XP didn't improve the performance, just the opposite. It slowed it down a bit. I don't have any problems with my VMs, having VT-x on or not, with or without IO APIC (just tested with an Ubuntu server VM).

[MarkCranness]

@devsk: Yes, that's what I did before I made my post, which displays this:

Device Manager Computer.png (24.29 KiB) Viewed 2338 times

(on my host) ... thus my comment about 'ambigious'.

[devsk]

@devsk: Yes, that's what I did before I made my post, which displays this:

Device Manager Computer.png

(on my host) ... thus my comment about 'ambigious'.

ahh...ok. I meant ACPI PC.

[Sasquatch]

But, why do you want to change it? Windows picks the right kernel to install without you messing it up.

[devsk]

But, why do you want to change it? Windows picks the right kernel to install without you messing it up.

Because the install is already there. I am booting a native partition containing XP.

I still don't understand why Intel VT gives a guru meditation in this case. May be I should just be happy with the performance that I am getting now and not expect major gains from Intel VT.

[Sasquatch]

But, why do you want to change it? Windows picks the right kernel to install without you messing it up.

Because the install is already there. I am booting a native partition containing XP.

I still don't understand why Intel VT gives a guru meditation in this case. May be I should just be happy with the performance that I am getting now and not expect major gains from Intel VT.

I told you above, there is no gain with VT on, only the opposite, a bit slower VM. Maybe they fixed that in recent versions, but it was an issue some versions back (2.1.x, maybe 2.2.x).