If you have enabled an option accept_mutex is set to on, worker processes will accept new connections by turn. Otherwise, all worker processes will be notified about new connections.  Some of the worker processes may just waste system resources if the volume of new connections is low.

Open your nginx.conf file and add a line in your events field "accept_mutex on;", 

events {
    worker_connections 200000;
    use epoll;
    accept_mutex on;

Referred from: http:/nginx.org/en/docs/ngx_core_module.html#accept_mutex