Liangxu Linux

Sep 4, 2024 · Fundamentals

Why Does TCP Send‑Q Exceed SO_SNDBUF? Inside Linux Kernel Buffer Mechanics

A Linux client sets SO_SNDBUF to 4096 bytes, sends 1 KB packets while the server never reads, yet the TCP Send‑Q grows to 14480 bytes because the kernel doubles the buffer size, adds overhead, and expands memory via GSO and sk_wmem scheduling.