Comment by monocasa

It's not the context switch that kills you for the most part, but the nature of the API and it's lack of direct access to the buffer cache and VMM layer. Making a stable FKSE leads to the same issues.

That's why Windows moved WSL2 to being a kernel running on hyper-v rather than in kernel. Their IFS (installable filesystem driver) stack screws up where the buffer cache manager is, and it was pretty much impossible to change. At that point, the real apples to apples comparison left NT lacking. Running a full kernel in another VM ended up being faster because of this.