Why is tcp_congestion_control=westwood set ?

[liushooter]

slv/template/2026.5.1.1510/ansible/cmn/optimize_system.yml

Line 14 in 086e249

net.ipv4.tcp_congestion_control=westwood

net.ipv4.tcp_congestion_control=westwood

Curious about the reasoning here — is there a benchmark behind this choice?

Westwood feels outdated to me: it was designed for lossy wireless links, and on the wired DC/bare-metal hosts validators run on
it offers no real advantage. Mainstream today is CUBIC (the kernel default), or BBR for high-RTT/lossy paths.

Is westwood a deliberate, tested choice, or carried over from older tuning guides? Thanks!

[liushooter]

BTW

slv/template/2026.5.1.1510/ansible/cmn/optimize_system.yml

Line 18 in 086e249

net.ipv4.tcp_low_latency=1

tcp_low_latency=1 is a no-op on modern kernels (obsolete since 4.14)

This line has no effect on any modern kernel and should be removed.

Why

The TCP prequeue mechanism this knob controlled was removed in kernel 4.14 (2017). The sysctl is kept only as a backward-compat stub — writing to it does nothing.

The kernel source marks it obsolete (v6.8, net/ipv4/sysctl_net_ipv4.c):

  /* obsolete */
  static int sysctl_tcp_low_latency __read_mostly;
  ...
  {
      .procname     = "tcp_low_latency",
      .data         = &sysctl_tcp_low_latency,
      .maxlen       = sizeof(int),
      .mode         = 0644,
      .proc_handler = proc_dointvec   // only stores the value; nothing in the kernel reads it
  }

Verified on 6.8.0-111-generic: sysctl net.ipv4.tcp_low_latency still returns = 1 (the key exists and doesn't error), but the setting has no actual effect.

On coverage

Worth noting given 4.14's footprint: 4.14 is still one of the most widely deployed older kernels (default on Amazon Linux 2, and Oracle Linux UEK R5) — and it's precisely the release that marked this knob obsolete.

So across the entire current kernel range (4.14 → 6.x) this parameter is a no-op. It only did anything on kernels < 4.14 (e.g. RHEL/CentOS 7's 3.10, Debian 9's 4.9), all of which are EOL and wouldn't be used to run a node.