Mixed-Precision Matmul: Throughput Gains with Accuracy Controls: Interview Drills

Interview drills

Interview Drills for Mixed-Precision Matmul: Throughput Gains with Accuracy Controls is anchored on Tokens or inferences per second at fixed quality target and overflow or underflow incidence per training or inference step.. Convert measurements into mechanism-backed decisions with clear owner accountability.

PROMPT
You observe regression in Tokens or inferences per second at fixed quality target and overflow or underflow incidence per training or inference step. for Mixed-Precision Matmul: Throughput Gains with Accuracy Controls. Explain root cause and release decision.

STRONG ANSWER
1. Defines workload and first failing mechanism.
2. Explains mechanism: Mixed precision increases matrix throughput by using lower-precision inputs such as FP16, BF16, or INT8 while accumulating in wider formats to reduce numerical error. Hardware tensor cores expose fast paths for these formats, but stability still depends on scaling strategy, calibration, and reduction order. For training, techniques like dynamic loss scaling and selective higher-precision layers preserve convergence while capturing most performance gains. For inference, quantization-aware calibration and outlier handling determine whether speedups hold at production accuracy thresholds.
3. Requests proving artifact: Precision policy sheet mapping operators to compute and accumulation formats with quality guardrails.
4. Proposes bounded fix + owner + rollback-safe validation.

WEAK ANSWER
Gives generic optimization ideas without mechanism proof or ownership.

AI accelerator deep dive

Sparse and mixed-precision wins require stable compiler lowering and runtime support coverage.

Concept diagram

SPARSE TENSOR EXECUTION

model graph -> compiler lower -> sparse or dense kernel path -> runtime scheduling -> SLA outcome

Metric graph

SPARSE REALITY CHECK

nominal sparsity      ████████████
real speedup          ██████
fallback overhead     █████

Metrics and artifacts to collect

• tensor-core occupancy

• fallback kernel rate

• sparse metadata overhead

• quality guardrail drift

Mini case study

Structured sparsity improved one layer family while unsupported operators forced dense fallbacks elsewhere.

Debug branches

• Track dense fallback counters

• Audit sparse-format conversions

• Check precision policy with quality gates

Senior review question

Ask: which first-principles bottleneck class explains the symptom, and what artifact proves it reproducibly?

Key takeaways

• Tie every accelerator claim to a reproducible workload slice and one primary metric trend.

• Prefer bounded fixes with clear owner and rollback boundary over broad tuning bundles.

Common pitfalls

• Optimizing synthetic kernels without production-shape validation.

• Reading average latency while ignoring p95 and p99 behavior.

• Declaring sparse or precision wins without fallback and quality evidence.

Interview answer expansion

A strong answer on Mixed-Precision Matmul: Throughput Gains with Accuracy Controls names the workload symptom, explains mechanism (Mixed precision increases matrix throughput by using lower-precision inputs such as FP16, BF16, or INT8 while accumulating in wider formats to reduce numerical error. Hardware tensor cores expose fast paths for these formats, but stability still depends on scaling strategy, calibration, and reduction order. For training, techniques like dynamic loss scaling and selective higher-precision layers preserve convergence while capturing most performance gains. For inference, quantization-aware calibration and outlier handling determine whether speedups hold at production accuracy thresholds.), and proposes one measurable validation plan.

Then it identifies owner and fallback action if the proposed fix under-delivers.

The goal is practical engineering reasoning, not keyword listing.