How can I measure the delay of system?

If you want 'real results', you should not rely on the mirror functionality of the switch for this, as you will never know how exactly (in which order) the switch copies the frames from 3+2 to the mirror port. The best option would be to capture the traffic of port 3 and 2 with a TAP for each port and with two systems with 'highly synchronized' clocks.

However: That's pretty much overhead (TAPs, two systems, etc.). If the expected delay is small (a few microseconds), you'll have to do it like described above, if you want to get 'real results'. If the expected delay is much larger (a few milliseconds) the approach with a switch mirror port and one capture system might be good enough.

Either way you need to calculate the delay between two identical frames in the capture file. That can be done with tshark and a script (perl, python, whatever).

tshark -nr input.pcap -T fields -e frame.number -e ip.id -e frame.time_relative

The output looks similar to this:

1       0xf038  0.000000000
2       0xf039  0.019413000
3       0xf038  0.02136700
4       0xf039  0.03316100

With the script you can find duplicate IP IDs and calculate the delta between the two time stamps. The delta values can be loaded into a spreadsheet software to create a chart.

Regards
Kurt