worker_cpu_affinity

Syntax: worker_cpu_affinity cpumask [cpumask...]

Default: none

Linux only.

With this option you can bind the worker process to a CPU, it calls sched_setaffinity().

 For example worker_processes     2; worker_cpu_affinity 01 10; worker_processes     4;  worker_cpu_affinity 0001 0010 0100 1000;  Bind each worker process to one CPU only.  worker_processes     2;  worker_cpu_affinity 0101 1010;  Bind the first worker to CPU0/CPU2, bind the second worker to  CPU1/CPU3. This is suitable for HTT

nginx可以使用多个worker进程，原因如下：

to use SMP to decrease latency when workers blockend on disk I/O 。to limit number of connections per process when select()/poll()。 is used The worker_processes and worker_connections from the event sections allows you to calculate maxclients value: 

max_clients = worker_processes * worker_connections

综上：2核是 01，四核是0001，8核是00000001，有多少个核，就有几位数，1表示该内核开启，0表示该内核关闭。