Top Nginx Performance Tweaks: Worker Processes and CPU Affinity Explained

All Nginx performance improvements start by editing the nginx.conf file.

1. worker_processes – number of worker processes

The default is one worker with a maximum of 1024 connections per process. Each worker runs a single thread and invokes various modules. If the modules are non‑blocking, the number of workers should match the number of CPU cores; if blocking I/O is possible, a few extra workers may be needed.

For example, when static files are read from a small‑memory server, disk I/O can block workers and degrade overall performance.

Typical setting: set the number of workers to the number of CPU cores (or cores × 2). Use top -1 to view core count.

# Edit nginx configuration
vi /usr/local/nginx/conf/nginx.conf
# Set workers, e.g., 4
worker_processes 4;
# Reload configuration
/usr/local/nginx/sbin/nginx -s reload
# Verify processes
ps -aux | grep nginx | grep -v grep

2. worker_cpu_affinity – binding workers to CPU cores

If each worker is heavily loaded, allowing multiple workers to compete for the same CPU can cause contention. Assigning each worker a dedicated core enables true parallelism on Linux.

Note: worker_cpu_affinity works only on Linux.

Configuration examples:

# 2‑core system
worker_processes 2;
worker_cpu_affinity 10 01;

# 4‑core system
worker_processes 4;
worker_cpu_affinity 1000 0100 0010 0001;

# 8‑core system
worker_processes 8;
worker_cpu_affinity 00000001 00000010 00000100 00001000 00010000 00100000 01000000 10000000;

These settings bind each worker to a specific CPU mask, eliminating CPU contention and improving throughput.