Count number of rehashing in unordered map

What is the right way to evaluate the unordered_map performance? [C++14]

In my code, I am using std::unordered_map very extensively in the order of billions of keys. For the purpose of performance I wished to know the behavior of unordered_map as how many times it had to rehash and all other parameter (how many buckets? How many buckets where empty before rehashing?). I know stl provides the number of buckets? But what else would be needed to profile or what do you use to analyze?