The linearRegression.fit() is too slow.

[zeng-hello-world]

https://github.com/mit-han-lab/amc/blob/040d83fe9f0288556c8afe363c190e763425a6fe/lib/utils.py#L130

[wu-leaf]

I don't understand why the export_model step need to use LinearRegression.fit(). The whole export_model process is very slow