research28 min studyLesson 1000 in Engineering

Choose a design point that meets the whole contract

Compare heterogeneous hardware and model changes through matched quality, loaded latency, complete costs, and reproducible evidence.

On this page

What you’ll understand

  • Filter candidate designs by quality, latency, capacity, and workload requirements.
  • Compute cost and energy per completed request at matched boundaries.
  • Distinguish calibrated models, measured prototypes, and reproducible application evidence.

Hardware-model co-design changes both the computation and the machine used to execute it. A smaller quantized model may fit a new accelerator and improve throughput while reducing quality; another mapping may preserve quality but add transfer latency. The useful comparison is a set of feasible design points under the application’s requirements. Define those requirements first, then collect evidence at matched load, input distribution, and accounting boundaries. A peak operations-per-second figure cannot settle a decision that also requires a minimum quality score, a tail-latency limit, and a sustainable operating cost.

Freeze the comparison contract before searching

Specify the task, evaluation data, quality metric, request shapes, arrival process, latency statistic, and required throughput. Include memory capacity, numerical tolerance, availability, and supported operators where they constrain deployment. A design that misses one mandatory requirement is infeasible for that decision even if it has excellent arithmetic efficiency. Keep its result in the research record, but do not rank it as a cheaper replacement for a system meeting the original contract.

Separate controlled ablations from complete-system comparisons. Holding the model fixed can isolate a mapping or hardware mechanism; changing quantization, architecture, or sparsity explores another design point. Both are valuable when labeled. Timeloop illustrates systematic architecture and mapping exploration, while MLPerf Inference defines concrete quality and scenario-based performance methodology. Neither eliminates the need to disclose the actual workload, versioned rules, tuning budget, and measurements used in a particular co-design claim.

F={d:qd≥qmin⁡, ℓd≤ℓmax⁡, Rd≥Rmin⁡, Md≤Mavailable}\mathcal F=\{d:q_d\geq q_{\min},\ \ell_d\leq\ell_{\max},\ R_d\geq R_{\min},\ M_d\leq M_{\rm available}\}
d indexes complete hardware-model configurations. q is a quality metric whose larger value is better, ℓ the declared latency statistic, R completed requests/s under the specified load test, and M required resident memory. Other mandatory constraints can extend the feasible set.↔ Scroll wide equations horizontally.

Match cost and energy denominators

For a steady interval, average included power divided by completed request rate yields energy per completed request. Include host, memory, networking, conversion, and idle allocation according to the declared boundary. If only successful deadline-qualified requests matter, use their rate and assign all spent energy to that same interval. Do not quietly divide one design’s board power by another design’s best kernel throughput. State whether replication, spare capacity, and utilization losses are part of the deployment budget.

Cost per request depends on provisioned capacity and achieved utilization as well as nominal device price. Include the hardware or rental boundary, software support, power, and any required auxiliary systems consistently. A design with lower cost per completed request at saturation may still need more replicas to handle a latency target or failure budget. Use the expected deployment demand rather than assuming every purchased device runs continuously at the benchmark’s maximum useful rate.

erequest=PincludedRcompleted,crequest=Chour3600Rcompletede_{\rm request}=\frac{P_{\rm included}}{R_{\rm completed}},\qquad c_{\rm request}=\frac{C_{\rm hour}}{3600R_{\rm completed}}
P is average watts over the same steady interval as R>0 requests/s, so e is joules/request. Chour is currency/hour for the declared resource boundary, giving currency/request. Deadline-qualified goodput can replace R when explicitly defined and measured consistently.↔ Scroll wide equations horizontally.

Demand evidence at the claimed level

An analytical ceiling, cycle simulation, synthesis estimate, implemented prototype, and production workload measurement support different claims. Describe the method and uncertainty for each design point. Calibrate cost models on representative observations, reserve validation cases, and explain residual errors. A simulation can guide search without proving physical timing or power. A measured prototype can prove one implementation’s behavior without establishing a result for a larger, differently connected system.

Release model artifacts, compiler and driver versions, placement plans, numerical settings, dataset IDs, warm-up, measurement intervals, and raw per-run summaries. Repeat experiments enough to characterize relevant variation and inspect tail behavior at the intended load. Report the feasible Pareto set rather than declaring one universal winner across incompatible objectives. The final choice should follow the application contract and evidence, while unresolved assumptions remain visible for the next experiment to test.

The lowest cost point may lack required capacity

Use fictional candidates tested under one quality metric and p99 latency rule. Require quality≥0.90 and p99≤10 ms. A achieves 2000 requests/s, quality 0.89, p99=7 ms. B achieves 1500 requests/s, quality 0.91, p99=8 ms at 6 currency units/hour and 600 W. C achieves 1200 requests/s, quality 0.92, p99=9 ms at 4 units/hour and 480 W. Deployment requires at least 1300 requests/s.

  1. A fails the mandatory quality threshold despite its high throughput. B and C pass quality and latency, but C’s tested capacity 1200 is below the required 1300 requests/s. B remains feasible among these single-instance candidates.

  2. At their stated operating points, B costs 6/(3600×1500)≈1.111×10⁻⁶ currency units/request. C costs 4/(3600×1200)≈0.926×10⁻⁶ units/request, but that lower ratio does not remove its capacity shortfall.

  3. Energy per completed request is 600/1500=0.4 J for B and 480/1200=0.4 J for C at the specified boundaries. Equal energy ratios and C’s lower saturated cost do not make the designs interchangeable for the deployment demand.

The result

B is the feasible choice within the stated single-instance candidate set. Replicating C would create another design point with new cost, routing, latency, and failure assumptions that must be evaluated explicitly.

Explore the model

Interactive lab

Interactive lab · roofline

A ceiling is evidence for one mechanism only

Reset, set Operational intensity I to 16 and Memory bandwidth B to 100. Predict the synthetic fixed compute ceiling 1000 GFLOP/s before Step. Reset, explicitly set I=16 and B=50, then Step: predict bandwidth ceiling 800 GFLOP/s. Playback traces the same hypothetical roof model. It has no quality score, request distribution, cost, tail latency, or power boundary, so it cannot choose a co-design winner.

A ceiling is evidence for one mechanism onlySynthetic roofline ceiling min(1000, B·I), in GFLOP/s, with B in decimal GB/s and I in FLOP/byte. Playback traces the roof without changing the selected kernel. This upper-bound model is not a measured throughput prediction, hardware comparison or price model. Current readings: Attainable ceiling: 640 GFLOP/s; Ridge intensity: 12.5 FLOP/byte; Ceiling regime: Memory-bound ceiling. All parameters are adjustable with the labeled controls below.Hypothetical roofline upper bound: 640 GFLOP per second at operational intensity 8 FLOP per byte and bandwidth 80 gigabytes per second.0.1110641101001000Operational intensity · FLOP/byte · log scaleCeiling · GFLOP/s · log scalePeak: 1000
Attainable ceiling / kernelBandwidth roof / traceCompute ceiling
Attainable ceiling
640 GFLOP/s
Ridge intensity
12.5 FLOP/byte
Ceiling regime
Memory-bound ceiling
t = 0 s

Synthetic roofline ceiling min(1000, B·I), in GFLOP/s, with B in decimal GB/s and I in FLOP/byte. Playback traces the roof without changing the selected kernel. This upper-bound model is not a measured throughput prediction, hardware comparison or price model. Parameter changes pause playback and recompute the model at the current elapsed time. Reset restores both parameters and returns time to zero. Playback starts paused. Adjust either parameter, then choose Play or Step.

Look forUse each model for the question it actually answers, then validate the complete design contract.

Check your understanding

Why is candidate C not a direct single-instance replacement for B under the worked deployment requirement?

Try it yourself

A fictional complete measured system draws 250 W and completes 500 requests/s at a cost of 3.6 currency units/hour. Compute energy and cost per completed request. A model change raises throughput but lowers quality from 0.91 to 0.89 when the minimum is 0.90; can it be treated as a feasible improvement under that requirement?

Take a moment to make a prediction or work it out on paper. Open a hint when you need one.

Give me a hint

Divide matched interval power and hourly cost by the completed rate, then apply feasibility before ranking.

Compare with the solution

Energy is 250/500=0.5 J/request. Cost is 3.6/(3600×500)=2×10⁻⁶ currency units/request. The changed model misses the quality minimum and is infeasible for that contract, regardless of its higher throughput. It can be reported as a separate research point, not an accepted equivalent improvement.

Take it with you

  • Define feasibility before comparing heterogeneous design points.
  • Match quality, load, units, and complete cost/energy boundaries.
  • Separate predictive models from implemented and measured application evidence.

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