[HippoBaro]

I am not sure I buy the underlying idea behind this piece, that somehow a lot of money/time has been invested into asynchronous IO at the expense of thread performance (creation time, context switch time, scheduler efficiency, etc.).

First, significant work has been done in the kernel in that area simply because any gains there massively impact application performance and energy efficiency, two things the big kernel sponsors deeply care about.

Second, asynchronous IO in the kernel has actually been underinvested for years. Async disk IO did not exist at all for years until AIO came to be. And even that was a half-backed, awful API no one wanted to use except for some database people who needed it badly enough to be willing to put up with it. It's a somewhat recent development that really fast, genuinely async IO has taken center stage through io_uring and the likes of AF_XDP.

[mmis1000]

Make os thread runs more efficient is like `faking async IOs (disk/network/whatever goes out from the computer shell) into the sync operations in a more efficient way`. But why would you do it at first place if the program can handle async operations at first place? Just let userland program do their business would be a better decision though.