Ascend Profiling Anomaly

Ascend Profiling Anomaly Discovery Skill

Purpose

Analyze Ascend NPU profiling data through three parallel pipelines:

1. Structure breakdown: step → structure (layer) → block / side → op → PMU judgement — answers where the time goes.
2. Anomaly discovery: step → device busy union → bubble detection → anomaly tags → soft attribution — answers what looks unnatural and where hidden issues may lurk.
3. Model architecture analysis: FIA timeline → pass boundaries → layer classification → per-layer sub-structure → communication pipeline → architecture summary — answers what is this model and how does each component execute. Produces a separate Markdown report file.

The core philosophy is separation of concerns: "anomaly exists" is a hard fact derived from device intervals; "why it exists" is a soft attribution that may require additional evidence. Even under weak profiling configurations (no stacks, no shapes, sparse host events), the skill must still reliably surface device idle bubbles and risk labels.

Reference Files — When to Read

Read these before starting analysis:

Pipeline Overview

The full state machine:

INGEST → INVENTORY → FACT_EXTRACTION → CANDIDATE_STEP_DETECTION →
STEP_GROUPING → MACRO_STEP_RESOLUTION → SEGMENTATION →
CLOCK_ACCOUNTING → ANOMALY_DISCOVERY → PERF_JUDGEMENT →
RECOMMENDATION → RENDER → DONE
                                        ↘
                          ARCHITECTURE_ANALYSIS → ARCH_REPORT_RENDER → ARCH_REPORT_SAVE

ANOMALY_DISCOVERY sits after CLOCK_ACCOUNTING and before PERF_JUDGEMENT. It receives already-segmented steps and structures, and runs the bubble detection pipeline on top of them.

ARCHITECTURE_ANALYSIS runs in parallel with PERF_JUDGEMENT, using the same segmented data from CLOCK_ACCOUNTING plus FIA timeline analysis. It produces a separate Markdown report file saved alongside the profiling data.

Data Hierarchy: Step → Structure → Block/Side → Op

Understanding how raw kernel data maps to each level is essential. Read references/kernel_data_guide.md for the full column schemas and parsing details. Here is the conceptual overview:

Level 0: Raw Kernels

Each row in kernel_details.csv represents a single device kernel execution — one invocation of an AI Core task, an AI CPU task, or an HCCL communication task. Key fields: Name, Task Type, Start Time(us), Duration(us), Wait Time(us), Accelerator Core, Stream ID, Input Shapes, Output Shapes.

Level 1: Step

A step is one training/inference iteration. Steps are identified by ProfilerStep#N user annotations or Iteration#N markers in trace_view.json. Each step defines a service window [S_i, S_{i+1}). All kernels whose start time falls within this window belong to step i.

At step level, compute:

• Total service time, device busy union, underfeed ratio
• Prelaunch gap, tail gap, internal bubbles
• Per-step anomaly tags and soft root-cause labels

Level 2: Structure (Layer)

Within a step, kernels form repeating structures — typically corresponding to model layers (e.g., transformer blocks, attention layers, MLP blocks). Segmentation identifies these by:

1. Repeating name-pattern sequences in the kernel timeline
2. Significant time gaps between kernel groups
3. User annotations marking layer boundaries (if present)

Each structure contains a contiguous span of kernels within the step window.

At structure level, compute:

• Structure wall time, device busy union within structure span
• Structure share of total step time
• Per-structure bubble metrics (is the bubble inside this structure or between structures?)

Level 3: Block / Side

Within each structure, kernels split into:

• Block (main compute path): The dominant chain of AI Core kernels forming the forward or backward pass of this layer. These execute on the main compute stream.
• Side (auxiliary ops): Everything else — small element-wise ops, communication (HCCL), AI CPU fallback ops, memory copies, synchronization events. These may execute on separate streams.

At block/side level, maintain four timing perspectives simultaneously:

• wall_ms — wall-clock time from first kernel start to last kernel end
• busy_union_ms — merged device-busy time (accounts for multi-stream overlap)
• kernel_sum_ms — arithmetic sum of all kernel durations (ignores overlap)
• total_cost_ms — sum of duration + wait for all kernels

Conclusions based on only one metric are incomplete. A block appearing heavy in kernel_sum but light in wall means high stream parallelism. A side appearing heavy in total_cost but light in duration means wait-anchor false hotspot risk.

Level 4: Op (individual operator)

The finest grain. Each op may produce one or many device kernels. Op-level analysis handles:

• Top ops by total cost vs. top ops by kernel duration (these rankings often differ)
• Wait-anchor detection: ops with wait_ratio > 0.95 and tiny duration but high total_cost
• AICPU classification: ops running on AI CPU instead of AI Core, classified by masked_ratio
• Small-op initial judgement: whether small individual ops are real inefficiencies or noise

Anomaly Discovery Pipeline (Detail)

Phase 1: BUILD_DEVICE_INTERVALS

For each step, collect all device kernel intervals from kernel_details.csv:

device_intervals = []
for each kernel row where Start_Time_us is within step window:
    s = max(step_start_us, row.Start_Time_us)
    e = min(step_end_us, row.Start_Time_us + row.Duration_us)
    if e > s:
        device_intervals.append(Interval(s, e))

Key rules:

• Clip kernel intervals to the step window boundary
• Apply communication dedup rules BEFORE interval statistics (see references/kernel_data_guide.md section on comm dedup)
• Include AI_CORE, AI_CPU, and HCCL tasks — all count as "device busy"
• When multiple streams exist, intervals from all streams are collected into the same set

Phase 2: MERGE_INTERVALS

Sort intervals by start time, merge overlapping ones:

merged = merge(device_intervals)  # see scripts/reference_host_gap_branch.py
busy_union = sum of merged segment durations

This produces the merged busy segments from which all bubble metrics derive.

Phase 3: GAP_CLASSIFICATION

From the merged segments, compute per-step metrics:

• service_ms = step window duration
• device_busy_union_ms = sum of merged segment durations
• underfeed_ms = service − busy_union
• underfeed_ratio = underfeed / service
• prelaunch_gap_ms = start(first_merged_segment) − step_start
• tail_gap_ms = step_end − end(last_merged_segment)
• internal_bubble_total_ms = sum of gaps between consecutive merged segments
• largest_internal_bubble_ms = max gap between consecutive merged segments
• bubble_count = number of inter-segment gaps

Phase 4: HOST_EVIDENCE_COLLECTION

For each bubble window (gap between merged segments, or prelaunch/tail gap), scan the same time range in host events from trace_view.json:

Host event categories to collect:

• cpu_op / python_function / user_annotation — general host activity
• AscendCL@* — ACL runtime events
• HostToDevice / torch_to_npu / aclrtMemcpy* / aclrtSynchronize* — sync/copy markers
• c10d / Hccl / hcom / StreamWaitEvent / Notify_Wait — communication markers

Compute overlap ratios:

• host_visible_coverage_ratio = fraction of bubble covered by any host event
• sync_marker_overlap_ratio = fraction covered by sync/copy markers
• comm_marker_overlap_ratio = fraction covered by communication markers

Phase 5: SOFT_ATTRIBUTION

For each significant bubble, assign probability-level labels based on overlap ratios:

Multiple labels can co-exist. These are explicitly NOT unique root causes.

Phase 6: ANOMALY_TAGGING

Apply the anomaly tags from references/rulebook.md decision tables. Core tags:

Bubble severity: DEVICE_IDLE_GAP_HEAVY, PRELAUNCH_GAP_HEAVY, TAIL_GAP_HEAVY, INTERNAL_BUBBLE_HEAVY

Risk tags: HOST_ORIGINATED_RISK, COMM_SYNC_RISK, WAIT_POLLUTION_RISK, WAIT_ANCHOR_FALSE_HOTSPOT, AICPU_EXPOSED_RISK, UNTRACED_HOST_BLOCKING_RISK, PARTIAL_CAPTURE_BOUNDARY, VARIABLE_SHAPE_SAME_TEMPLATE

Phase 7: WAIT_ANCHOR_SCAN

At op level, scan for false hotspots:

wait_ratio = wait_us / (duration_us + wait_us)
if wait_ratio > 0.95 and duration_us < 10.0 and total_cost_rank <= 10:
    tag WAIT_ANCHOR_FALSE_HOTSPOT

These ops absorb idle wait time and appear expensive, but their kernel execution is negligible. Demote them in root-cause ranking.

Phase 8: GROUP_AGGREGATION

Aggregate step-level metrics by step_group_id:

• Compute avg, median, P90, P95 for each bubble metric
• recurring_bubble_pattern = true if ≥60% of steps in group have bubble_count > 0
• dominant_idle_pattern = whichever of prelaunch/internal_bubble/tail contributes most

Phase 9: PRODUCE_OUTPUT

Merge anomaly results with structure breakdown. The report MUST include:

Hidden Issue Discovery section

• Dominant step/group bubble metrics (service, busy_union, underfeed_ratio)
• Raw kernel evidence table: for each top bubble window, list the kernel(s) immediately before and after the gap — their names, task types, durations, streams — so the human expert can locate the exact spot in the timeline
• Top 5 bubble windows with timestamps, scope, and host evidence
• Bubble periodicity statistics across the step group
• Host evidence coverage assessment
• Soft root-cause labels with evidence chains
• Follow-up sampling recommendations

Bubble-first Summary (fixed 5-question template)

1. Are there significant device idle bubbles?
2. Which step type/group do they concentrate in?
3. Are they primarily prelaunch / tail / internal / inter-step?
4. Is there significant host-originated risk?
5. Is evidence sufficient for root cause? If not, say so explicitly.

Structure-Level Bubble Drill-Down

For the dominant step, break down bubble contributions per structure:

• Which structure(s) contain the largest internal bubbles?
• Are bubbles concentrated at structure boundaries (between layers) or within structures?
• For structures with large bubbles, what are the surrounding kernel names and task types?

Model Architecture Analysis Pipeline (Separate Markdown Report)

This pipeline produces a standalone Markdown report file that documents the model architecture as reverse-engineered from profiling data. Read references/architecture_report_template.md for the full template, formatting rules, and analysis techniques.

The report is saved as model_architecture_report_<profiling_dir_name>.md in the profiling or output directory.

When to produce the architecture report

Always. Every profiling analysis MUST produce this report alongside the anomaly discovery output. The architecture report provides essential context that makes the anomaly findings interpretable.

Architecture Analysis Phases

Phase A1: FIA_TIMELINE_ANALYSIS

Use FusedInferAttentionScore (FIA) invocations as the primary structural marker:

1. Extract all FIA kernels from kernel_details.csv (match by name containing FusedInferAttentionScore)
2. Sort by Start Time(us)
3. Classify each FIA as prefill (duration > 10ms) or decode (duration < 1ms)
4. Determine pass count: num_passes = total_FIA / FIA_per_pass
5. Identify phase transitions by timestamp gaps between prefill and decode FIA clusters

Phase A2: PASS_BOUNDARY_DETECTION

For each forward pass, determine:

• FIA index range (e.g., #0–#94)
• Time span (absolute timestamps)
• Wall time from first kernel to last kernel
• Average prefill FIA duration
• Total kernel count

Cross-pass variation (FIA duration, wall time) should be noted — it may reveal KV cache growth or memory pressure effects.

Phase A3: LAYER_CLASSIFICATION

For each layer (delimited by consecutive FIA invocations), extract the kernel sequence and classify:

Build a summary table: Layer Type | Layer Range | Count | Characteristics

Phase A4: CROSS_VERIFICATION

Count key ops per pass and verify they match the layer classification:

• FIA count should equal layer count
• DispatchFFNCombine count should match MoE+DFC layer count
• GroupedMatmul count should match MoE+GMM layers + decode layers
• MoeGatingTopK count should match all MoE layers (DFC + GMM + decode)

Discrepancies indicate classification errors — resolve before proceeding.

Phase A5: PER_LAYER_SUBSTRUCTURE

For EACH distinct layer type, analyze the kernel execution sequence:

1. Group kernels by functional role (attention, projection, TP comm, MoE routing, expert dispatch, expert FFN, post-MoE norm, next-layer prep, EP comm, sampling)
2. Measure wall time per functional group
3. Identify which stream each group runs on
4. Compute timing breakdown: Component | Wall time | Share of layer
5. Note anomalies specific to the layer type (warm-up overhead in layer 0, extra kernels in transition layer, AICPU ops that should be on AI_CORE)

Present as kernel sequence trees with timing annotations and stream labels. See the template for the exact tree notation format.

Phase A6: DECODE_ANALYSIS

Decode layers require separate analysis because they have fundamentally different cost profiles:

• FIA duration drops dramatically (prefill 28ms → decode 0.2ms)
• Communication (especially all-to-all for EP) often dominates
• Expert compute shifts from fused (DFC) to explicit (GroupedMatmul)

Produce a dominant costs table and explain why the cost profile differs from prefill.

Phase A7: COMMUNICATION_PIPELINE

Document the multi-stream overlap strategy:

1. Map each stream to its purpose (main compute, AI_CPU comm, HCCL, alltoall)
2. Measure overlap ratios between streams
3. Draw an ASCII pipeline diagram showing how communication hides behind compute
4. Compute what fraction of total communication is hidden (overlapped)
5. Explain the kernel_sum >> wall relationship

Phase A8: ARCH_REPORT_RENDER

Assemble all findings into the Markdown report following the template in references/architecture_report_template.md. All 10 required sections must be present:

1. Configuration Context
2. Model Architecture Determination (evidence chain table)
3. Forward Pass Boundaries (per-pass table)
4. Layer Classification (type table)
5. Cross-Verification Table
6. Per-Layer Sub-Structure (kernel sequence trees + timing breakdowns for EACH layer type)
7. Decode Phase Analysis (dominant costs + prefill vs decode comparison)
8. Communication Pipeline Structure (stream table + ASCII pipeline diagram)
9. Layer-to-Layer Variation (comparative table)
10. Model Architecture Summary (ASCII model diagram + execution timeline)

Phase A9: ARCH_REPORT_SAVE

Save the report as model_architecture_report_<profiling_dir_name>.md. Inform the user of the file location.

Critical Constraints

• Never skip anomaly discovery because root cause is unclear. Bubble facts are hard conclusions; root cause labels are soft conclusions. Both must always be reported.
• Never call a high-wait tiny-duration op a real hotspot without checking wait-anchor risk.
• Never ignore local bubbles just because the step is device-bound overall.
• Never use only one timing metric — always maintain dual clock accounting (wall_ms + busy_union_ms + kernel_sum_ms + total_cost_ms) at block/side level.
• Always output insufficient_evidence or possible_untraced_host_blocking when host evidence is sparse — never silently omit the anomaly section.
• Always include raw kernel context around reported bubbles — the kernel names, task types, durations, and stream IDs immediately before and after each bubble gap.
• Use layered certainty language: declarative for facts, possible / probable / insufficient evidence for root causes.
• Always produce the model architecture Markdown report as a separate file — never fold it into the anomaly output alone.
• Never skip per-layer sub-structure analysis. Every distinct layer type must have its own kernel sequence tree with timing breakdown and stream annotations.
• Always include the evidence chain table in the architecture report — the reader must see how layer count and pass structure were determined from raw FIA data.
• Always cross-verify op counts against layer classification before finalizing the architecture report. Discrepancies must be resolved or explicitly noted.

Graceful Degradation

Output Contract Summary

Every analysis must produce TWO outputs:

1. Anomaly Discovery Output

The anomaly_discovery top-level object containing: enabled, dominant_group_id, global_device_gap_analysis, step_group_anomalies, bubble_windows, wait_anchor_ops, soft_root_cause_summary, requires_host_followup, confidence.

Each step result must include bubble metrics, anomaly tags, and soft root-cause labels.

For the full JSON schema, read references/schema.json.

2. Model Architecture Report (Markdown file)

A standalone Markdown file saved as model_architecture_report_<profiling_dir_name>.md containing all 10 required sections from the architecture template. Read references/architecture_report_template.md for the full specification.

The report must include at minimum:

• Evidence chain proving layer count and pass structure
• Layer classification table with all distinct layer types
• Per-layer kernel sequence trees with timing breakdowns for EACH layer type
• Communication pipeline structure with stream overlap diagram
• Model architecture ASCII summary diagram and per-pass execution timeline

The architecture report is the primary deliverable for understanding model structure. It must be self-contained — a reader should be able to understand the full model execution without referring to the anomaly output.

Recommendations

Each recommendation must include scope (global/step_group/structure/side/op), followup_required, evidence_gap, and priority (P0–P3).

Common follow-up patterns:

• High bubble + missing stacks → re-profile with with_stack=true
• Missing shapes + unstable grouping → record_shapes=true
• High host risk + low evidence → host-side sampling / thread view
• High wait pollution → check communication and sync paths
• Large inter-structure bubble → check host-side layer dispatch latency