Tuning Linux TCP BBR, Epoll & File Descriptors for Loader.io Stress Tests

Before Nginx or PHP ever see a packet, the Linux network stack governs SYN queues, socket buffers, and congestion windows. Proper sysctl tuning prevents dropped handshakes when 10,000+ clients connect simultaneously from Loader.io.

BBR + Fair Queueing (fq)

Enabling net.ipv4.tcp_congestion_control = bbr paired with net.core.default_qdisc = fq maximizes throughput across transcontinental links with non-zero packet loss while keeping queueing delay minimal.