I know ippsRSADecrypt uses pthread to speedup decription.But unless the whole program exits,ipp will leaves an useless thread for each calling process/thread. For most ssl servers,each connection will be dispatched to a seperate thread.This will leaves a lot of uselses thread even RSA routine ends.
See below,the bold texts shows the conclusion above.
Ipp is threaded with OpenMP. OpenMP runtime may internally maintain the threading it used. If the application is threaded at the high level, you can link with static non threaded IPP library, it can disable IPP threading.