Measure lower-range performance for infeasible trials

docs/harness-ablation/qwen235b-thinking-prefill-ttft-20260510.md

@@ -26,7 +26,9 @@ Both runs were launched through `python3 -m aituner.cli study tune`; no proposal
 
 The table below is the raw per-iteration performance for a Fig18-style plot. Use this table as `perf[i]`; do not replace missing points with `max(perf[:i+1])`.
 
-Metric: `best_request_rate_per_gpu` from that trial's own `result.json`. `NA` means the proposed config did not produce a feasible point under the SLO, either because the engine/probe failed or because every sampled probe was infeasible.
+Metric: `best_request_rate_per_gpu` from that trial's own `result.json`. `NA` means the proposed config did not produce a feasible point in the measured search range, either because the engine/probe failed or because every sampled probe was infeasible.
+
+Important caveat: these runs were produced before the lower-range fallback fix. For same-parallel-size runtime patches, AITuner inherited the incumbent `sampling_u` as the new search floor. If the config was infeasible above that floor, the old worker wrote `NA` without searching below the floor. Therefore the `NA` entries below are not complete Fig18-quality raw performance points; they are "no feasible point above inherited floor." A rerun with the fixed worker is required to fill their true lower-load performance.
 
 | Variant | iter1 | iter2 | iter3 | iter4 | iter5 | iter6 | iter7 | iter8 | iter9 | iter10 | iter11 | iter12 |
 | --- | ---: | ---: | ---: | ---: | ---: | ---: | ---: | ---: | ---: | ---: | ---: | ---: |

docs/harness-ablation/qwen27b-chat-0-8k-ttft4s-tpot25-20260510.md

@@ -26,7 +26,9 @@ The previous no-harness run was affected by the `dash0` migration and had many e
 
 The table below is the raw per-iteration performance for a Fig18-style plot. Use this table as `perf[i]`; do not replace missing points with `max(perf[:i+1])`.
 
-Metric: `best_request_rate_per_gpu` from that trial's own `result.json`. `NA` means the proposed config did not produce a feasible point under the SLO. `stop` means the harness stopped before launching another GPU trial.
+Metric: `best_request_rate_per_gpu` from that trial's own `result.json`. `NA` means the proposed config did not produce a feasible point in the measured search range. `stop` means the harness stopped before launching another GPU trial.
+
+Important caveat: these runs were produced before the lower-range fallback fix. For same-parallel-size runtime patches, AITuner inherited the incumbent `sampling_u` as the new search floor. If the config was infeasible above that floor, the old worker wrote `NA` without searching below the floor. Therefore the `NA` entries below are not complete Fig18-quality raw performance points; they are "no feasible point above inherited floor." A rerun with the fixed worker is required to fill their true lower-load performance.
 
 | Variant | iter1 | iter2 | iter3 | iter4 | iter5 | iter6 | iter7 | iter8 | iter9 | iter10 | iter11 | iter12 |
 | --- | ---: | ---: | ---: | ---: | ---: | ---: | ---: | ---: | ---: | ---: | ---: | ---: |

src/aituner/worker.py

@@ -539,25 +539,34 @@ def run_trial(trial_spec_path: Path) -> dict[str, Any]:
                     payload=payload,
                 )
 
-            search = binary_search_max_feasible(
+            primary_search = binary_search_max_feasible(
                 low=trial.search.low,
                 high=trial.search.high,
                 tolerance=trial.search.tolerance,
                 max_probes=trial.search.max_probes,
                 evaluator=evaluator,
             )
-            best = search.best_feasible_payload
-            result = {
-                "study_id": trial.study_id,
-                "trial_id": trial.trial_id,
-                "status": "completed",
-                "config_patch": to_jsonable(trial.config_patch),
-                "best_sampling_u": search.best_threshold if best is not None else None,
-                "best_request_rate": best.request_rate if best is not None else None,
-                "best_pass_rate": best.pass_rate if best is not None else None,
-                "best_request_count": best.request_count if best is not None else None,
-                "probes": [
-                    {
+            search_for_best = primary_search
+            best = primary_search.best_feasible_payload
+            best_source = "primary_search"
+            fallback_search = None
+            original_search_low = float(study.search.low)
+            inherited_search_floor = float(trial.search.low)
+            if best is None and inherited_search_floor > original_search_low:
+                fallback_search = binary_search_max_feasible(
+                    low=original_search_low,
+                    high=inherited_search_floor,
+                    tolerance=trial.search.tolerance,
+                    max_probes=trial.search.max_probes,
+                    evaluator=evaluator,
+                )
+                if fallback_search.best_feasible_payload is not None:
+                    search_for_best = fallback_search
+                    best = fallback_search.best_feasible_payload
+                    best_source = "lower_range_fallback"
+
+            def serialize_probe(probe: ThresholdProbe[ProbePayload]) -> dict[str, Any]:
+                return {
                     "threshold": probe.threshold,
                     "feasible": probe.feasible,
                     "payload": {
@@ -569,11 +578,49 @@ def run_trial(trial_spec_path: Path) -> dict[str, Any]:
                         "latency_summary": probe.payload.latency_summary,
                     },
                 }
-                    for probe in search.probes
-                ],
+
+            all_probes = [
+                *primary_search.probes,
+                *((fallback_search.probes if fallback_search is not None else [])),
+            ]
+            result = {
+                "study_id": trial.study_id,
+                "trial_id": trial.trial_id,
+                "status": "completed",
+                "config_patch": to_jsonable(trial.config_patch),
+                "best_source": best_source,
+                "best_sampling_u": search_for_best.best_threshold if best is not None else None,
+                "best_request_rate": best.request_rate if best is not None else None,
+                "best_pass_rate": best.pass_rate if best is not None else None,
+                "best_request_count": best.request_count if best is not None else None,
+                "probes": [serialize_probe(probe) for probe in all_probes],
             }
-            if best is None and search.probes:
-                last_probe = search.probes[-1]
+            if fallback_search is not None:
+                result["primary_search"] = {
+                    "low": inherited_search_floor,
+                    "high": trial.search.high,
+                    "best_sampling_u": primary_search.best_threshold
+                    if primary_search.best_feasible_payload is not None
+                    else None,
+                    "best_request_rate": primary_search.best_feasible_payload.request_rate
+                    if primary_search.best_feasible_payload is not None
+                    else None,
+                    "probes": [serialize_probe(probe) for probe in primary_search.probes],
+                }
+                result["lower_range_fallback"] = {
+                    "triggered": True,
+                    "low": original_search_low,
+                    "high": inherited_search_floor,
+                    "best_sampling_u": fallback_search.best_threshold
+                    if fallback_search.best_feasible_payload is not None
+                    else None,
+                    "best_request_rate": fallback_search.best_feasible_payload.request_rate
+                    if fallback_search.best_feasible_payload is not None
+                    else None,
+                    "probes": [serialize_probe(probe) for probe in fallback_search.probes],
+                }
+            if best is None and all_probes:
+                last_probe = all_probes[-1]
                 result["all_infeasible_diagnostics"] = {
                     "threshold": last_probe.threshold,
                     "request_count": last_probe.payload.request_count,

tests/test_core_flow.py

@@ -2062,6 +2062,90 @@ class CoreFlowTests(unittest.TestCase):
             self.assertEqual(rows[0]["outcomes"][0]["request_id"], "r1")
             self.assertEqual(rows[0]["outcomes"][0]["sampling_u"], 0.1)
 
+    def test_run_trial_falls_back_below_inherited_search_floor(self) -> None:
+        with tempfile.TemporaryDirectory() as tmp:
+            tmp_path = Path(tmp)
+            study_path = _write_study_assets(tmp_path)
+            payload = json.loads(study_path.read_text(encoding="utf-8"))
+            payload["search"]["max_probes"] = 2
+            study_path.write_text(json.dumps(payload), encoding="utf-8")
+            study = load_study_spec(study_path)
+            store = StudyStore(tmp_path / ".aituner" / "studies")
+            store.init_study(spec_path=study_path, study=study)
+            state = StudyState(
+                study_id=study.study_id,
+                best_trial_id="trial-0001",
+                best_parallel_size=1,
+                best_sampling_u=0.5,
+                best_request_rate=2.0,
+                best_request_rate_per_gpu=2.0,
+                next_trial_index=2,
+                best_by_parallel_size={
+                    "1": {
+                        "trial_id": "trial-0001",
+                        "parallel_size": 1,
+                        "best_sampling_u": 0.5,
+                        "best_request_rate": 2.0,
+                        "best_request_rate_per_gpu": 2.0,
+                    }
+                },
+                trials=[],
+            )
+            proposal = Proposal.from_dict(
+                {
+                    "observation": "runtime patch",
+                    "diagnosis": "measure even if worse than incumbent",
+                    "config_patch": {"env_patch": {}, "flag_patch": {"max-num-seqs": 2}},
+                    "expected_effects": ["measure"],
+                }
+            )
+            trial, _ = store.materialize_trial(study=study, state=state, proposal=proposal)
+            self.assertEqual(trial.search.low, 0.5)
+
+            def fake_replay(requests, **kwargs):
+                passing = len(requests) <= 1
+                return (
+                    [
+                        RequestOutcome(
+                            request_id=request.row_id,
+                            success=True,
+                            ttft_ms=10.0 if passing else 10000.0,
+                            tpot_ms=5.0 if passing else 1000.0,
+                            prompt_tokens=request.prompt_tokens_hint,
+                            completion_tokens=request.completion_tokens_hint,
+                        )
+                        for request in requests
+                    ],
+                    False,
+                    "",
+                )
+
+            process = mock.Mock()
+            process.poll.return_value = 0
+            with mock.patch("aituner.worker.subprocess.Popen", return_value=process):
+                with mock.patch("aituner.worker._wait_for_server_or_exit", return_value=None):
+                    with mock.patch("aituner.worker._terminate_process_tree", return_value=None):
+                        with mock.patch("aituner.worker._replay_requests", side_effect=fake_replay):
+                            result = run_trial(Path(trial.artifact_dir) / "trial_spec.json")
+
+            self.assertEqual(result["status"], "completed")
+            self.assertEqual(result["best_source"], "lower_range_fallback")
+            self.assertEqual(result["best_sampling_u"], 0.375)
+            self.assertEqual(result["best_request_rate"], 0.1)
+            self.assertEqual(result["primary_search"]["low"], 0.5)
+            self.assertIsNone(result["primary_search"]["best_request_rate"])
+            self.assertEqual(result["lower_range_fallback"]["low"], 0.0)
+            self.assertEqual(result["lower_range_fallback"]["high"], 0.5)
+            self.assertEqual(result["lower_range_fallback"]["best_request_rate"], 0.1)
+            self.assertEqual(
+                [probe["threshold"] for probe in result["primary_search"]["probes"]],
+                [0.75, 0.625],
+            )
+            self.assertEqual(
+                [probe["threshold"] for probe in result["lower_range_fallback"]["probes"]],
+                [0.25, 0.375],
+            )
+
     def test_materialize_trial_does_not_mutate_input_state_trials(self) -> None:
         with tempfile.TemporaryDirectory() as tmp:
             tmp_path = Path(tmp)