Crosspost from /WSL2-Linux-Kernel - .wslconfig "processors"

[just-Bri]

https://github.com/microsoft/WSL2-Linux-Kernel/issues/188

So there is some basic documentation for the wslconfig options available. One thing I am not sure about is what "processors" actually relates to. I have a 4 core 8 thread cpu, when I set the wslconfig processor option to 2, does that assign 2 physical cpu cores to the VM? Or does that allow 2 threads to the VM?

[therealkenc]

Documentation for .wslconfig is here.

Which SMT thread goes to work is up to the Windows scheduler. Shorter, simpler answer: you get two virtual processors, which you can see in /proc/cpuinfo. Neither threads nor cores are "assigned".

[just-Bri]

I'm trying to figure out what is being used on the hardware side. If you look at my other issue from WSL2-Linux-Kernel you'll see what I mean. And I even have a screenshot from the documentation in that thread where it says "processors" but does not define whether or not that is a core or a thread.

/proc/cpuinfo only tells me what the VM knows about, but it doesn't know how many physical cores, or threads, on the hardware CPU it is using.

[therealkenc]

Was curious so did a test to look. The logical CPUs aren't being scheduled evenly, either because they are (as a practical matter) assigned at startup or because there is some strong processor affinity going on. On my 16C/32T box with processors=8, I ended roughly the same logical processors doing the heaving lifting on two runs of "sysbench cpu --threads=8 run". Either way the work was not allocated by physical cores vs logical cores, AFAICT. So short answer, as a practical matter, "processors" means "logical processors". Which logical processors is implementation detail.

Run 1:

Run 2:

[maltem-za]

Just wanted to add that @therealkenc's answer is confirmed by a comment in the example .wslconfig file: "Sets the VM to use two virtual processors"