# EXP-SIMFID-Q30-LATENCY-EXPANSION: remaining Fixed/Trace × PD/P cases

> Status: completed (2026-07-18). The low-load Fixed cases below are retained
> as sensitivity evidence; the later 4096-token, 1.125 req/s/GPU Fixed matrix
> is the primary comparison. Trace-PD is excluded from this card.

## Question and fixed boundary

Does the same graph-aligned Frontier configuration that selected the correct
winner on Trace-PD also select the real vLLM winner when either the arrival/
prefix state or the decode phase is removed? This is a selection test, not an
SLO/capacity evaluation.

| Case | Input / output | arrival and cache | Applicable objectives |
|---|---|---|---|
| Fixed-PD | 2048 / 128 | 129 uniform requests; `t'=t/TP`; prefix cache off | mean/p90 TTFT, TPOT, E2E |
| Trace-P | exact held-out input, arrival, session and complete block-16 prefix relation / 1 | same TP-normalized 129-row trace; prefix cache on | mean/p90 TTFT, E2E; TPOT=N/A |
| Fixed-P | 2048 / 1 | 129 uniform requests; `t'=t/TP`; prefix cache off | mean/p90 TTFT, E2E; TPOT=N/A |

All cases use Qwen3-30B-A3B BF16, community vLLM 0.20.0, H20, `TP∈{1,2,4}`
and `MNS∈{8,16,32,64}`, MBT=8192, chunked prefill, three fresh-server trials
per cell. The fixed QPS is the Trace-PD base offered rate (`129/600` req/s per
GPU), hence the global arrival rate is multiplied by TP. It makes throughput
per GPU comparable without claiming that different TP values see identical
cluster-level load.

## Simulator and real contracts

- Frontier uses commit `deadc4a…`, `piecewise`, the frozen CUDA-event profile
  for prefill/mixed batches and KERNEL_ONLY profile for captured pure decode.
- Trace-P reuses the already verified graph buckets/KV capacities because the
  server CLI is unchanged from Trace-PD. The only workload change is `OSL→1`.
- Fixed-P/PD disables vLLM prefix caching on both sides. Before freezing their
  simulator surfaces, a no-request server-start preflight records the actual
  graph captures and KV-block capacities for every `(TP,MNS)`; no request
  latency or winner is used as calibration.
- Each real result verifies every request's input/output usage and row-vector
  digest. `OSL=1` produces JSON `null` TPOT samples and is never converted to
  zero.

## Decision rule and cost

For every applicable objective, compare the complete 12-cell simulator and
pooled three-trial real surface: winner match, selected-config real regret,
and non-tied pair direction agreement. A simulator crash or missing request
metric is a coverage failure, not a high-latency cell.

The no-request Fixed runtime preflight is capped at 2 H20-GPUh. Each 36-run
real surface is estimated at 13 nominal / 41 worst-case H20-GPUh, plus CPU-only
Frontier replay. Launch logs record the resolved inputs, paths, and duration.

## Result: exact-selection fidelity is not stable across workload phase/state

All three real surfaces completed 36 valid fresh-server trials (12
TP×MNS cells × 3 trials), each with 129/129 exact-usage requests.  The
corresponding 12-cell Frontier replays completed all 129 requests per cell.
The following table compares the simulator argmin with the pooled real argmin;
`regret` is the selected simulator configuration's real relative latency
regret.  It deliberately reports exact winner equality rather than treating a
high pairwise-order agreement as success.

| Case | Objective | Frontier winner | Real winner | Match | Real regret |
|---|---|---|---|---:|---:|
| Trace-P (OSL=1) | TTFT mean | TP4/MNS16 | TP4/MNS64 | no | 3.2% |
| Trace-P (OSL=1) | TTFT p90 | TP4/MNS16 | TP4/MNS8 | no | 0.4% |
| Trace-P (OSL=1) | E2E mean | TP4/MNS16 | TP4/MNS64 | no | 3.2% |
| Trace-P (OSL=1) | E2E p90 | TP4/MNS16 | TP4/MNS8 | no | 0.3% |
| Fixed-PD | TTFT mean/p90 | TP4/MNS16 | TP4/MNS16 | yes | 0.0% |
| Fixed-PD | TPOT mean | TP1/MNS16 | TP4/MNS32 | no | 14.0% |
| Fixed-PD | TPOT p90 | TP1/MNS16 | TP4/MNS8 | no | 13.4% |
| Fixed-PD | E2E mean | TP1/MNS16 | TP4/MNS32 | no | 26.9% |
| Fixed-PD | E2E p90 | TP1/MNS16 | TP4/MNS8 | no | 25.7% |
| Fixed-P (OSL=1) | TTFT/E2E mean/p90 | TP4/MNS16 | TP4/MNS8 | no | 1.5--3.6% |

The decisive failure is Fixed-PD: its TPOT and E2E pairwise orders are exactly
reversed on all 48 informative pairs.  Thus the graph-aligned profile can
preserve coarse TP ordering yet still choose the wrong configuration for the
serving objective.  The prior Trace-PD success is therefore a workload-specific
success, not evidence that Frontier has solved config tuning.

## Superseding primary Fixed workload

The subsequent pressure sweep changed the Fixed shapes to 4096->256 and
4096->1, raised the offered load to 1.125 req/s/GPU, and used 257 requests per
cell. Those Fixed-PD/PO results, together with Trace-PD and Trace-PO, are
reported in the consolidated
[Qwen30/Qwen235 selection-regret report](../../docs/simulator-tuning/frontier-selection-regret-qwen30-qwen235-20260719.md).

Under that primary Fixed-PD workload, Frontier's selected config is 58.0%
slower for real mean TTFT and 56.2% slower for real p90 TTFT than the
real-hardware optimum. The low-load table above must therefore not be quoted
as the final Fixed-PD result.
