Which time should be regarded as the actual write latency?

[Darleen71]

DRAMsim3/src/controller.cc

Line 260 in 2981759

simple_stats_.AddValue("write_latency", wr_lat);

I'd like to consult you on this. The latency of a write transaction starts to be calculated only when it reaches this line of code. However, in reality, when the ReturnDoneTrans function returns the write transaction, the data of the write transaction has already been written into the DDR. Why is this? Which time should be regarded as the actual write latency? Thank you for your explanation!