void print_pipeline(struct connectdata *conn) function will be called every time when Curl_add_handle_to_pipeline called.
there is no need for the call. when conn_list is large, cpu will be 100% and the hot point of cpu is the calling of print_pipeline.
this function do nothing just print some debug info . I think there is no need to call this function.
Thanks a lot for this report. I agree completely and I've now pushed a change (commit 231b23acbba2) that removes this function.
Case closed!
thank you for your reply.