2D graphics performance issue when increasing the number of cores

[roland651]

Hi,

to increase the performances of Adobe Lightroom in a Windows 7 VM, I tried recently to increase the number of cores in my Windows 7 VM and I noticed a serious drop in 2D graphics performances.

I first believed it was due to some regression in recent versions of VirtualBox, so I did some benchmarks (using PassMark 9) in the VM with VirtualBox 5.2.x and 6.1.x, and I got the same performance drop for 2D graphics, whatever the VirtualBox version, when I increased the number of cores in the VM. So, it's not a regression.

I have a very powerful machine, with 16 physical cores and 128 GB RAM, so I was able to plot the PassMark 2D score vs the number of cores (2, 4, 8 or 16) in the VM. Then I exported my VM to VMware Player, and I did the same benchmark. The attached image 'figure_2D.png' shows the results (higher score is better). As you can see, the 2D graphics score for VirtualBox linearly decreases as the number of cores increases. The 2D score is divided by ~4 between 2 cores and 16.

However, this is not the same for VMware, where one can see a small decrease of 15% between 2 cores and 16.

I also plotted the CPU score of PassMark vs the number of cores in the VM (image 'figure_CPU.png', higher score is better). For this benchmark, VirtualBox and VMware perform the same until 8 cores, but VMware gives a much better result for 16 cores.

I tried many parameter tweaks in VirtualBox but I was not able to improve the situation. I also tried with another PC that has less cores, and I saw the same performance drop...

Note that the performance drop I see in PassMark scores (in a Windows 7 VM) reflects what I see as a user in the windows 7 VM. This is not an artefact of using PassMark in a VM. For example, with 16 cores in a VirtualBox VM, moving a window is painfully slow. The CPU load is very high even when I do nothing, the fans are at maximum speeds, etc. Those problems do not arise in VMware player: the CPOU load is low, and the VM is very snappy, whatever the number of cores.

To me, there should be no interaction between increasing the number of cores and the 2D graphics performance. It's clearly a bug or perhaps a side effect of the way multicore processing is done in VirtualBox...

My hardware: HP Z820 Workstation with two Intel Xeon CPU E5-2687W 0 @ 3.10GHz, 16 cores, 32 threads and 128 GB RAM, graphic card id an Nvidia Quadro K2000

Host system: Ubuntu Linux 18.04, 64 bits

Guest system: Windows 7 Professional SP1, 64 bits, 4GB RAM in the VM, guest additions installed, 256 MB video RAM

[roland651]

2D score

[roland651]

CPU score