worker_cpu_affinity

By Default, without setting worker_cpu_affinity directive in nginx.conf, linux kernel will spread all nginx’s worker all over CPUs.

I have 4 logical CPUs on my server, which is CPU0 – CPU3

Cpu0  :  2.9%us,  0.9%sy,  0.0%ni, 88.9%id,  7.2%wa,  0.0%hi,  0.2%si,  0.0%st
Cpu1  :  1.8%us,  0.6%sy,  0.0%ni, 95.3%id,  2.2%wa,  0.0%hi,  0.1%si,  0.0%st
Cpu2  :  2.4%us,  0.7%sy,  0.0%ni, 94.3%id,  2.5%wa,  0.0%hi,  0.1%si,  0.0%st
Cpu3  :  1.9%us,  0.7%sy,  0.0%ni, 96.7%id,  0.6%wa,  0.0%hi,  0.0%si,  0.0%st

Using default setting, nginx’s worker always bind to those 4 logical CPUs. which is has “f” bitmask

# taskset -p 12348
pid 25748's current affinity mask: f
# taskset -p 12349
pid 25749's current affinity mask: f
# taskset -p 12351
pid 25751's current affinity mask: f
# taskset -p 12352
pid 25752's current affinity mask: f
# taskset -p 12353
pid 25753's current affinity mask: f

CPU affinity is represented as a bitmask (given in hexadecimal), with the lowest order bit corresponding to the first logical CPU and the highest order bit corresponding to the last logical CPU.
Examples: