Liangxu Linux
Oct 27, 2024 · Fundamentals
Why Does TCP Send‑Q Exceed SO_SNDBUF? Inside Linux Kernel Buffer Mechanics
A client sends 1 KB TCP packets every second with a 4 KB SO_SNDBUF while the server never calls recv(), yet the observed Send‑Q grows to 14 480 bytes, revealing how the Linux kernel doubles the buffer size, uses sk_wmem_queued, and expands write queues via GSO and memory scheduling.
GSOSO_SNDBUFSend-Q
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