rlm_perl and checksimul

hi: I am using freeradius 3.0.4 comes with rhel 7.1. I want to write a checksimul perl script. but it seems won't be called. I create a rlm_perl instance "check_login", and put it under "default" site: session { check_login } and at perl script I write my code at finction below: sub checksimul { &radiusd::radlog(L_INFO, "check_login: I am here"); return RLM_MODULE_OK; } but "radiusd -X" show my code is not be called after user authentication. the code works fine if I put it at "authroize" or "post-auth" section. I don't know if I miss some steps or I met a bug..