Measures latency between Linux packet RX and UDP poll() return.
Newest Linux kernel packet timestamping interface SO_TIMESTAMPNS_NEW requires kernel v5.1 or later.
If using an older kernel, you could use plain SO_TIMESTAMP which as been around forever but is not Y2038-safe.
Generate data:
$ echo "a" | nc -n4u -w1 127.0.0.1 9001
Example output:
$ ./timestamp
Latency between packet and poll return: 123292 ns
realtime before poll = 1653046981 s 030207629 ns
packet time = 1653046982 s 345149554 ns
realtime after poll = 1653046982 s 345251334 ns
monotime after poll = 47723 s 713906136 ns
realtime after recv = 1653046982 s 345272846 ns
See timestamping.txt in kernel-doc: https://www.kernel.org/doc/html/latest/networking/timestamping.html
Monotime is provided to correspond with kernel timestamps in perf script.
Used https://github.com/bibiboot/kernel_so_timestamp to understand how to setup the control message and iovec.