Failure Signature Debug and Triage: Inputs and Outputs

Inputs and outputs contract

Inputs and Outputs for Failure Signature Debug and Triage focuses on Mean time to root cause (MTTR) and signature classification accuracy.. The purpose is to turn link observations into mechanism-backed actions with explicit owners and release-safe validation.

Use this contract for architecture, controller firmware, PHY, and validation handoffs. Missing inputs create expensive late-stage rework and inconclusive debug loops.

INPUTS
  - workload distribution and QoS target
  - firmware revision, controller policy profile, timing registers
  - data-rate / voltage / temperature operating state
  - training snapshot and reliability policy status

OUTPUTS
  - bottleneck classification with command-level evidence
  - owner-signed mitigation proposal
  - before/after trend for latency, bandwidth, and reliability
  - regression matrix with rollback triggers

Ownership split

OWNERSHIP LAYERS - Failure Signature Debug and Triage

protocol/MAC     : link firmware owner
PHY digital      : SerDes architect
PHY analog       : PHY analog designer
SI/PI + package  : SI/PI owner
validation       : validation owner

SerDes deep dive

Compliance fixtures, BERT/eye scan, failure signature debug, and production screening for SerDes signoff.

Concept diagram

VALIDATION DEBUG
compliance-test-fixtures -> bert-and-eye-scan -> closure

Metric graph

MARGIN TREND
healthy ██████
failing ██

Reports and artifacts

• eye margin log

• BER/FEC counter sheet

• coefficient dump

• JTOL/compliance margin report

Mini case study

A corner board failed link training after package update; isolating lane skew and PI noise restored margin.

Debug branches

• Classify failure: training, eye, jitter, deskew, or runtime drift

• Capture coefficient and margin artifacts under fixed thermal tags

• Correlate SI/PI measurements before retuning adaptation

Senior review question

Ask: which latency, bandwidth, and reliability evidence proves this SerDes topic is closed under real traffic?

Key takeaways

• Always tie controller and PHY counter shifts to application latency and throughput outcomes.

• Lock firmware timing profile, thermal condition, and DIMM state before comparing SerDes captures.

Common pitfalls

• Chasing peak bandwidth while ignoring p99 latency and fairness tails.

• Changing timing guardbands without separating SI noise from scheduling issues.

• Declaring closure without reliability gates, fault injection, and regression replay.

Handoff explanation

Inputs extend beyond timing registers. SERDES analysis inputs include traffic distribution, address map, queue policy, training state, SI/PI condition, thermal state, and firmware version.

Outputs must be action-ready: Mean time to root cause (MTTR) and signature classification accuracy., artifact packet (Failure signature taxonomy with exemplar logs per class.), bottleneck class, owner, expected gain, and rollback scope. "Bandwidth improved" without this packet is not signoff-ready.

The safest handoff is a before/after evidence set: environment tags, traces, hypothesis, chosen fix, rejected alternatives, and regression criteria.