Still very slow SMP operation on 3.0.2 with Linux 64-bit host and Windows XP 32-bit guest

[Matti Rintala]

I upgraded from 2.x.x to 3.0.2. My host is Opensuse 11.1 64-bit, and I'm running Windows XP 32-bit guest on a Intel Core 2 processor.

Running my old virtual machine (from 2.x.x) works as before, but utilises naturally only 1 CPU. When I create a new virtual machine with 2 CPUs, it is unbearably slow. Installing Windows XP and its updates took hours, and running the virtual machine after it is equally slow. Later editing virtual machine settings to allow only 1 CPU changes nothing in this respect, the virtual machine is still slow.

Host CPU utilisation drops when the guest is idle, but when the guest is actually doing something, both CPU cores show almost 100 % most of the time.

[Matti Rintala]

VirtualBox logfile

[rggjan]

I can confirm this with XP 32-bit and Ubuntu 64-bit, exactly the same problem.

When turning off "IO-Apic" however, (and thus also disabling the 2-processor feature) then it is fast as before again...

[Sander van Leeuwen]

As stated in the known limitations section some Intel CPUs (yours included) and all AMD CPUs do not support any hardware optimization that's needed when turning on the IO-APIC. Will be fixed in a future release.

This is a duplicate defect (search for IO APIC)

[Matti Rintala]

Ok, good to know this is a known thing.

However, I'd like to point out that the Known Limitations section in the user manual for version 3.0.2 only says: "Bad performance with 32-bit guests on AMD CPUs. This affects mainly Windows and Solaris guests, but possibly also some Linux kernel revisions." I didn't find anything about "some Intel CPUs".

Same thing when I searcher this bugtracker for IO APIC, the only relevant bug I found even contained "AMD-V only" in the title. :-)

[Yuhong Bao]

"As stated in the known limitations section some Intel CPUs (yours included) and all AMD CPUs do not support any hardware optimisation that's needed when turning on the IO-APIC. " To be more precise, Intel introduced this hardware optimization (which relates to the APIC TPR) in the G0/M0 stepping of 65nm Core 2 processors, which means older steppings of the 65nm Core 2 processors as well as all older Intel CPUs with VT will not have it. Suggestions is to either replace the CPU with at least G0/M0 stepping 65nm Intel Core 2 processors, using a newer version of Windows (Windows Server 2003 SP2/Vista/Server 2008) that has Lazy IRQL, making this optimisation unnecessary, or disable the IO-APIC. I wonder how many such older CPUs with VT are in the installed base?

[Sander van Leeuwen]

#4392

The next VirtualBox version will have a software solution for Intel CPUs that support 64 bits mode. (similar to the AMD-V solution)