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Power: 2 streams and a 2.0 GHz clock pinned by a new checkMaxFreq SETTINGS check (performance governor + scaling_max_freq = fixed clock) take line rate from 80 W to 29.7 W package, qualified 96 s zero-loss; measured on the bench: streams buy scheduling headroom not watts (C1-parked threads, lonelier spinners boost harder), relaxed cpu_dma_latency never reaches deep idle (scheduler spreads wakeups, ~2% residency), offlining E-cores saves 1.7 W and is wire-invisible mid-run, the cliff is TX starvation below 1.6 GHz (1.2 GHz sags to ~18 G, zero errors)

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flamingcow
2026-08-19 14:11:19 -07:00
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docs/hardware.md
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@@ -12,12 +12,13 @@ Module identities, EEPROM honesty (and why the X520 needs `allow_unsupported_sfp
## Host tuning (resets every reboot; re-apply before trusting results)
Required for zero baseline loss; without them baseline loss is 0.02–0.3% and masks cable faults.
Required for zero baseline loss (without them baseline loss is 0.02–0.3% and masks cable faults) and for the power budget.
1. **CPU governor → `performance`** on all cores. Biggest single contributor: under powersave, cores idle at 400 MHz, ramp too slowly, and drop frames at startup.
2. **Disable adaptive coalescing**: `ethtool -C <dev> adaptive-rx off adaptive-tx off rx-usecs 25 tx-usecs 25`. Syntax/values differ per driver — re-derive per NIC.
3. **Rings deep**, raised toward the max via `ethtool -G` (the tool asks RX 8160 / TX 4096; ixgbe takes it as-is). Effect was not isolated in testing; don't claim it as a proven win.
4. **Socket buffers**: no sysctl change needed — the tool forces `SO_RCVBUFFORCE`/`SO_SNDBUFFORCE` (needs root) past the 4 MB `rmem_max` clamp.
2. **CPU max frequency → 2.0 GHz** (`scaling_max_freq`, all cores). Under the performance governor this is a pinned clock, not a ceiling, and it is the power budget: ~30 W package at line rate against ~80 W unbounded (measurement.md, "Power"). The value is host-silicon-bound — 1.6 GHz still holds line rate with thinner margin, 1.2 GHz cannot fill the wire — so re-derive it on new host silicon and re-qualify zero-loss.
3. **Disable adaptive coalescing**: `ethtool -C <dev> adaptive-rx off adaptive-tx off rx-usecs 25 tx-usecs 25`. Syntax/values differ per driver — re-derive per NIC.
4. **Rings deep**, raised toward the max via `ethtool -G` (the tool asks RX 8160 / TX 4096; ixgbe takes it as-is). Effect was not isolated in testing; don't claim it as a proven win.
5. **Socket buffers**: no sysctl change needed — the tool forces `SO_RCVBUFFORCE`/`SO_SNDBUFFORCE` (needs root) past the 4 MB `rmem_max` clamp.
Verify a clean run shows `tx frames == rx frames` exactly before a run counts.