Probably the biggest argument against doing what you describe is that the status quo gives you control over scheduling which fds to service (of the ones that ar

Probably the biggest argument against doing what you describe is that the status quo gives you control over scheduling which fds to service (of the ones that are active). If you processed incoming network data in strict FIFO order, a single host on your LAN could totally DoS your system by flanking you with incoming data. That host would never get TCP flow-controlled because if you're processing anything, you're processing his obnoxiously voluminous input. If he was just on FD among many, you would service him once in a while, but then you would service other clients. While you're servicing other clients, he gets TCP flow-controlled, so he doesn't singlehandedly demand all your attention.