On: Unix Domain Sockets vs Loopback TCP Sockets (2014)

[duped]

What's in the way of TCP hitting the same performance as unix sockets, is it just netfilter?

[noselasd → duped]

TCP has a lot of rules nailed down in numerous RFCs - everything from how to handle sequence numbers, the 3-way handshake, congestion control, and much more.

That translates into a whole lot of code that needs to run, while unix sockets are not that much more than a kernel buffer and code to copy data back and forth in that buffer - which doesn't need a lot of code to make happen.

[woodruffw → duped]

I believe the conventional wisdom here is that UDS performs better because of fewer context switches and copies between userspace and kernelspace.

[foobiekr → woodruffw]

No. This is exactly the same. Think about life of a data gram or stream bytes on the syscall edge for each.

[woodruffw → foobiekr]

I’m not sure I understand. This isn’t something I haven’t thought about in a while, but it’s pretty intuitive to me that a loopback TCP connection would pretty much always be slower: each transmission unit goes through the entire TCP stack, feeds into the TCP state machine, etc. Thats more time spent in the kernel.

[foobiekr → woodruffw]

Yea but those aren’t context switches.

[foobiekr → duped]

The ip stack.