Scenario: Hollow Coverage Closure

Scenario

Functional coverage hits 98% on headline bins, but a customer plugfest finds an interop failure on a rare cross of burst length, error recovery, and power-state exit that was never stimulated.

OBSERVED METRIC
High bin percentage with zero hits on P0 cross-coverage interactions tied to customer workloads.

45-MINUTE INTERVIEW FLOW
0-5: scope traffic and SLA context
5-15: map first failing VIP transition
15-25: identify proving artifacts
25-35: propose bounded fix with owner
35-45: state validation matrix and rollback

Common pitfalls

• Celebrate percentage closure without cross-bin risk review.

• Waive critical crosses without silicon or interop correlation.

• Conflate toggle coverage with spec-meaningful functional bins.

Scenario debrief

Score candidate response on traffic framing, timing proof, mitigation boundedness, and regression discipline.

request stream -> controller policy -> VIP timing behavior -> measured outcome

latency/bandwidth trend

Debrief prompts

1. Which VIP timing or queue behavior fails first in evidence?

2. Which smallest safe controller, PHY, or policy change addresses it?

3. Which benchmark + counter gate proves closure under production 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 VIP 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.