Solved by tom in post #2 
              
              
                Yes. 

No. 

You want warmup, probably.
You don’t want to use time.time for timing. Use time.perf_counter. Or use Jupyter/IPython and %timeit
One thing to keep in mind with GPU benchmarking is to do the syncing before looking at the wall clock (before start and before end).

Best regards 
Thomas