VirtualBox not maxing out CPU?

Cheetah Designs · 2 Mar 2011 at 15:17

Is there something that I may not have enabled in settings that would prevent VirtualBox from maxing out my i3 CPU?

SiriusB · 2 Mar 2011 at 15:25

Is your VM set to use 2 CPUs?

If I recall, VB will only use one core on the host system if set to 1 CPU.

Cheetah Designs · 2 Mar 2011 at 15:38

Ah right...that makes a little more sense.....it seems to be using around 25% of my CPU though when it's maxed out. With the 25% being spread over all cores (according to windows)

SiriusB · 2 Mar 2011 at 15:40

Oh, hmm. I may be wrong then.

What is it exactly you are trying to do?

Cheetah Designs · 2 Mar 2011 at 15:46

Well I am doing compiling stuff in Ubuntu in a VirtualBox and it doesn't max out the CPU.

I have also run super-pi to check that its not just that task, but it isn't.

EniGmA1981 · 2 Mar 2011 at 21:50

Super-PI doesn't max my C2D either, highest I get is low 70%'s... check it with Prime95 or IBT (with coretemp running to show core load)

SiriusB · 3 Mar 2011 at 12:07

I wonder if something has changed. I recall running Folding@Home inside a VirtualBox VM a while back and that quite happily maxed my CPUs. Perhaps they have limited the amount it can use to prevent the host system from being bogged down?

Cheetah Designs · 3 Mar 2011 at 12:43

Ah...I need to set the number of CPUs to 2 in the virtual box settings...

I thought that Virtualbox would spread the load automatically if I put 1 CPU.

I have the option to select up to 4 CPUs i think (probably due to hyperthreading)...should I....or do I leave it at 2?

When I select 2 CPUs it uses a maximum of 50%...and compilation takes 1 min 55 seconds....when I select 4 it goes up to about 90% sometimes and takes 2 mins 12 seconds...

....no idea why its slower...

aln · 3 Mar 2011 at 12:48

Nevermind you've answered yourself.

That said, some works loads will be slower with HT on. Some server distributors specifically advise that it be turned off, as the overhead isn't worth it. Its very specific to what you're doing though.

Cheetah Designs · 3 Mar 2011 at 12:50

aln said:
25% sounds like its using 1 of your 4 threads (if your cpu has 4). Tell it to use more if you want more, but this will require a reboot of the VM afaik.

This appears to be true.....but that said....the 25% is split over all the Threads.