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Im using WindowsXP guest on win7 host and its horrible slow when I enable more cores of my Q9300.
With one core it works just like 2.x.x did. When I enable 2 cores it slows down and when I enable 4 cores it gets to crawling speeds up to the point where it is useless and host CPU utilization is horrible high. It uses all 4 cores just to open up IE.

It locks up pretty regularly and it was impossible to install windows XP when I had 2 cores enabled. I was able to install just one instanc out of 10 trys but even this locked up later when using.

Same problem here, i tried on 2 machines (Macbook and Desktop both with OSX host and intel core 2 duo).

I am having the same problem but with a windows 7 64 bits guest in an Ubuntu 64 bits host with VB 3.0 with phenom x4 940 processor. If i use 1 processor i am having a decent performance but when i select more then 1 processor the performance is slowed to near unusable.

SawyerX wrote:Im using WindowsXP guest on win7 host and its horrible slow when I enable more cores of my Q9300.
With one core it works just like 2.x.x did. When I enable 2 cores it slows down and when I enable 4 cores it gets to crawling speeds up to the point where it is useless and host CPU utilization is horrible high. It uses all 4 cores just to open up IE.

It locks up pretty regularly and it was impossible to install windows XP when I had 2 cores enabled. I was able to install just one instanc out of 10 trys but even this locked up later when using.

Yes, I have the same problem. I wrote about them to the following thread: http://forums.virtualbox.org/viewtopic.php?f=7&t=19527 (It is in "Linux hosts" rather than "Windows guests" forum).

Your description matches my experience to a T.

I have some suspicion that hard drive access may be the real culprit (if more than one core tries to access the drive at the same time).

I experience a very slow Windows Guest with 2 CPUs here too.

I run a WindowsXPPro SP3 guest inside an Ubuntu Jaunty Host. Both 32Bit. VirtualBox ist 3.0.2. I enabled SMP and booted the Windows Guest. Everything works fine, but only one CPU is used. I searched the forum an found one thread: http://forums.virtualbox.org/viewtopic.php?f=2&p=84602 and another one http://forums.virtualbox.org/viewtopic.php?f=2&t=19878. As i was unable to install the "ACPI Multiprocessor PC" via the device-manager i tried:
a) manually replacing the DLLs as descibed here: http://www.handaware.com/multiprocessor_XP.html
b) enable SMP support via the HAL-Tools from here: http://www.hardware.info/en-US/news/ym2 ... t_anymore/

Both times a got a Windows Guest horribly slow, using all CPU resources.
As a work-around setting the number of CPUs available to 1 fixes the problem, but this leaves me with a single-core Guest running an SMP-aware virtualbox. Not quiet optimal...

All hints are very welcome.
Regards, Jens

@jensen,
You might want to read Chapter 13. Known limitations in the Users Guide.

Perryg wrote:@jensen,
You might want to read Chapter 13. Known limitations in the Users Guide.

Ok this is how it feels when

The following Guest SMP (multiprocessor) limitations exist: Bad performance with 32-bit guests on AMD CPUs.

kicks in
Missed that part in the first place. Thanks Perryg!. So i guess i will come back in VirtualBox 3.2 or something like this.

Ok but with hyper-threading if you use a 32 bit host you will not see any improvement using SMP I don't believe. My system is 32 bit and I run (4) vm's at the same time. They work as fast as the host. IMHO. With the exception of moving huge files which are slower.

Might be worth upgrading to v3.2 now cos of this (taken from the Changelog):

VMM: guest SMP performance improvements

At least kick the wheels of the newer version and see does it do anything for performance.