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Comment by contrarian_ | Hacker News Reader

Yep, I was actually debating whether I'd mention sendmmsg/recvmmsg in my original post but I left it out. Definitely an option for UDP, but you're out of luck if your game server uses TCP (surprisingly many do) because you have to recv from each socket separately.

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There may still be some options depending on the structure of your server and where the added CPU load is hurting most, for example, shunting IO to a thread/threadpool where futex() calls (if necessary) only occur for every N IO requests, rather than pay the syscall price for every IO on the main thread. But that might introduce new latency/ordering problems all of its own

The majority of online games use TCP these days with good prediction it’s more reliable than UDP.

Latency is more important than reliability for online gaming because the world state instantly gets stale. Instead of retransmit you want latest snapshot. I'd be curious to find out in what online games that is not the case.

Latency isn’t an issue today what so ever, it’s not like UDP also has a magical lower latency it had in the past because of smaller packets and slower computers but today?

Online games work today with fixed ticks and polling usually at half of full frame rate which means that the server updates and polls the client 30 or 60 times a second or any other even multiplier of the expected synced frame rate.

I'm calling bullshit. TCP has to retransmit lost packets whereas UDP can keep on going without waiting for transmission. Ephemeral data like controller input or past game states can be ignored because that time has passed, while TCP is still trying its best to get the packets there in order and reliably.

Latency is still absolutely an issue. I play games from Japan with my friends in the states and I often have a ping of 140 ms or so. That is latency, and properly implemented games (Rocket League, for example) will deal with it using UDP among other techniques.

Slower paced games can still use TCP though because latency issues are less sensitive.

>This fixed and predictable rate pretty much means that UDP is near pointless and games that still don’t have a predictable tick rate and use UDP tend to be a rubber banding lag fest.

You're wrong. Head of line blocking is a real thing that happens very often in TCP.

Edit: parent poster removed that part of the comment between me reading and submitting a reply

Nope, sorry but you're completely wrong on this. UDP is better because head of line blocking will causes large delays during packet loss.

Source: I used to write networking stacks for realtime games.

It really depends on the type of game.

If it's a latency sensitive (like a twitch FPS), UDP is the way to go. Having up to date data is more important than having all the data.

If it's a synchronized game (like a turn based game or an RTS where all clients run at the same logic framerate), or not latency sensitive (an MMO like WOW), TCP is fine and probably easier.

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