Hi Eddie, thank you very much for the help, here are the tests and results I have according to your suggestion. I hope this can help you to better identify the reason of the issue.
Summary:
1) MLNX-OS verion of SN2700 is 3.5.0202
2) I configured global pause frame, but it does not work. Switch port receiving too fast will get into an abnormal state. Please see my attachement for details.
3) I have not successfully setup PFC according to the documents because I cannot enable it with ubuntu 12.04. It seems I need to upgrade to 14.04 or above to make it work. I will post my result when I managed to get it running.