When the NIC collects packets and notifies the CPU once per batch to reduce CPU load, packets arrive later by the time spent collecting.
Why The NIC collects packets for a set time or count before raising an interrupt → Effect Packets wait while the batch fills → On screen A small rise in latency. Usually tiny, but ms-scale if overdone
Use adaptive coalescing, tune the values for game servers (ethtool -C).
Ballpark numbers
Typically tens to hundreds of µs. That’s negligible for most games, but aggressive settings can push it into the ms range.
On the graph
Always high · Round-trip time within the same data center
Where to look
Check the current coalescing settings (adaptive-rx, rx-usecs, rx-frames) with ethtool -c, and compare ping round-trip time to another server in the same data center before and after changing them
Confirmed if
rx-usecs is set high (hundreds of µs or more), and lowering it cuts round-trip time within the data center by about the same amount
Ruled out if
Round-trip time unchanged after lowering it: not this cause