I would create the issue directly in pytorch/pytorch as dynamo should now be part of the core framework. The code owners could cross-post it into the pytorch/torchdynamo repo if needed.
You may be encountering dynamic shapes in your model, causing recompilation. The periods of low gpu utilization could be compilation time, and the second epoch could be better if the majority of input shapes have been seen before. You can use .explain or recompilation profiler (see Troubleshooting guide)
Posting issues on pytorch/pytorch is also ok, we may end up redirecting all issues there soon, but it’s true we originally asked for issues to be filed on pytorch/torchdynamo since that’s where we developed before launch.