Liangxu Linux

Oct 21, 2024 · Fundamentals

Why Does TCP Send‑Q Exceed SO_SNDBUF? Deep Dive into Linux Kernel Buffer Mechanics

A Linux client that sets SO_SNDBUF to 4096 bytes and sends 1 KB packets to a non‑receiving server sees the TCP Send‑Q grow to 14480 bytes, revealing how the kernel doubles the buffer size, uses sk_wmem_queued, and expands memory via GSO‑driven size goals.