Solved by twister9458 in post #7 
              
              
                Thank you @ptrblck. 
As I’m working on aws services, I found that when I moved all my dataset to my EC2 instance, where I have my PyTorch/Cuda optimized notebooks, the GPU started to be used, which speeded it up. 
Though, the usage of the GPU is still low, and doesn’t reach 80% unless I input big lo…