Why is 'accept_mutex' 'on' as default in Nginx?

mutex, nginx

Solution

As of nginx mainline version 1.11.3 (released 2016-07-26), `accept_mutex` now defaults to `off`. This is partly because the new `EPOLLEXCLUSIVE` flag provides the benefits of `accept_mutex` without the extra overhead.

Problem

I found 'accept_mutex' is 'on' as default in Nginx as follows: http://wiki.nginx.org/EventsModule Then does accepting connection require mutex? Why?

Original source