https://github.com/10gen/mongo/blob/af39933b7e530cf1e582093fa06197ec6dd7799a/src/mongo/db/storage/wiredtiger/wiredtiger_record_store.cpp#L2182

    // Implicit construction of StringData:
    metricsCollector.incrementOneCursorSeek(c->uri); 

This line of code implicitly constructs a StringData from a const char*, which results in a call to strlen every time we seek on a record store cursor. While this is not an enormous cost, it has shown up in some profiles I've taken.