We use mean Average Precision (mAP) to evaluate the performance. Please refer to 
https://en.wikipedia.org/wiki/Evaluation_measures_(information_retrieval)#Average_precision
Or 
https://darren1231.pixnet.net/blog/post/347752732-machine-learning-map%28mean-average-precision%29-%E8%A9%B3%E7%B4%B0%E8%A7%A3%E8%AA%AA

for detailed explanation of Average Precision.