Network perfomance degradation while passing from 5 to 6 CPUs on a 12 cores Intel CPU.

[earizon]

I have an Intel Core(TM) i7-10850H CPU with "cores", with a native Windows 11 hosting an Ubuntu Box on top of VirtualBox 7.

Virtual Box clearly states not to use more than 6 CPUs in the guest VM in order to avoid decreased performance. I also noticed that performance is degraded (at least on Windows 11) when using more than 5 processors ("half minus one"). When I add the sixth one, networking and Firefox on the guest machine start running very slow, and pages loading blocks "forever". Not only network, but already loaded pages looks to block (probably caused by starvation or lock contentions in internal Firefox threads waiting for network response).

I used ​https://webglsamples.org/aquarium/aquarium.html for example as "benchmark" page. With 6 CPUs it takes much more time to load, and once loaded, performance is unstable. With 5 CPUs, page loading is much faster and the rendering performance stays constants at 13-14 fp/sec.

I use an Intel PRO/1000 T Server (82543GC) as virtual network.

I just found this old bug (from 2012) that can be related: https://www.virtualbox.org/ticket/10157

[fth0]

You're missing the fact that your CPU only has 6 cores with hyperthreading (​Intel Core i7-10850H Processor). According to some older Intel documentation, hyperthreading roughly adds 30% of performance, so you cannot really build on that. In consequence, you should give the host and the guest a fair share of the 6 cores.