[joatmon-snoo]

Someone more familiar with kernel workings than me should clarify, but my understanding is that IO generally happens via a syscall which requires the thread/process in question to context switch between userspace and kernel space, which can be very expensive. By enabling IO polling in userspace, you get to avoid that context switching.

[int0x80]

Yes. Instead of using a syscall to get/issue events you use a mapped ring buffer. See https://lwn.net/Articles/743714/