On the one hand, I have built two projects that are almost the same but one is written in Labview 2018 and the other is written in NXG 3.0.2. The performance of program in LV2018 is obviously better than that in NXG 3.0 and in LV2018 I can achieve a higher IQ rate without buffer error.
On the other hand, I used the example project "FM demodulation" which is shipped with Both LV2018 and NXG. With the same parameters and configuration of USRP, the performance of program in LV2018 is still better than the other and it seemed that the same code written in NXG costs more time generally.
I sincerely hope that the performance in NXG will be improved in the near future because I prefer to establish my project with NXG in class. Thanks a lot for all engineers working for NXG here!!