X520 live as the product NIC: rate buckets re-keyed to read time (one shared clock, one commit per drained batch) with the backward smear as a settled window — each completed bucket enters once, donates excess to the nearest earlier deficits once, locks for display when nothing later can refill it (per-sample recompute double-counted excess and read >20G on a 20G wire); timestamp machinery deleted (ts.go, SO_TIMESTAMPING, rx_filter=ALL check) after the audit confirmed the buckets were its sole consumer; testDriver ixgbe; RollBall mailbox hardened against orphaned-command completions (never sample status before a poll gap, value from the same block read, devad/reg echo required — a killed session's 7.60 read answered a PHY ID as 0x0006); full hardware pass: 20.00G flat both directions, zero errors, ECD 42m, SNR +7.4dB

counters.go

@@ -47,7 +47,7 @@ var nicRxStatsByDriver = map[string][]string{
 		"mac_remote_faults.nic",
 	},
 	// The 82599 exposes no jabber, fragment, illegal-byte or fault counters
-	// (divergence: docs/open-questions.md).
+	// (docs/nics/x520/).
 	"ixgbe": {
 		"rx_crc_errors",
 		"rx_missed_errors",