Much Lower Result & GPU Problem

Hi, I use only 1 GPU(GXT 1080Ti 11GB) for training this model. Limited by memory of GPU, I set the batchsize=4 instead of 16 in your code. And I trained the model only on Market-1501 dataset instead of 10 datasets. The result is mAP = 0.385818, r1 precision = 0.627969 much lower than your paper said. So there are two problems.
1. How many GPUs you used in this experiment? I wonder whether the batchsize mostly influence the accuracy.
2. If I can't get the whole 10 datasets and only use 1 dataset for training and testing, how much will the result fall?
Thank you for your wonderful work. Looking forward to your response.