inference-kernel-ncu-profile

name	inference-kernel-ncu-profile
last_validated	"2026-05-29T00:00:00.000Z"
description	Capture per-kernel CUDA hardware-counter data (occupancy, achieved warps active, regs/thread, smem/block, DRAM throughput, arithmetic intensity, branch divergence %, warp-stall reason %) from a live vLLM inference pod via an `ncu` debug sidecar (no production image rebuild). Outputs `.ncu-rep` + per-kernel CSV. Scoped via `--kernel-name` to avoid the 10-100x kernel-replay slowdown that an unscoped ncu attach would impose on serving. Pairs with `inference-kernel-profile` (nsys: absolute kernel duration + cuda-graph timeline) and `zymtrace-anchored-query` (sample- share + kernel-name resolution). Triggers on "ncu", "nsight compute", "kernel internals", "occupancy", "register pressure", "shared memory", "DRAM bandwidth", "roofline", "arithmetic intensity", "warp stalls", "branch divergence", or any combination of "ncu / nsight-compute / occupancy / regs / smem / dram / roofline" with "vllm / kimi / glm / deepseek / inference".
allowed-tools	["Bash(kubectl:debug,*)","Bash(kubectl:exec,*)","Bash(kubectl:cp,*)","Bash(kubectl:get,*)","Bash(ncu:*)","Bash(jq:*)","Bash(sha256sum:*)","Read","Write"]

inference-kernel-ncu-profile

Purpose

Capture per-kernel hardware-counter data from a live vLLM inference pod without rebuilding the production image. Uses kubectl debug --share-processes to attach an ncu-enabled sidecar to an existing pod. The sidecar replays a small number of launches of each named kernel with the hardware-counter set enabled and writes .ncu-rep files into a sidecar emptyDir that you extract via kubectl cp.

The three sibling skills cover complementary kernel-profile dimensions:

Question	Tool	Skill
What kernels run + relative sample-share?	zymtrace	zymtrace-anchored-query
Absolute per-kernel duration (ns), CUDA graph timeline, NVTX ranges	nsys	inference-kernel-profile
Per-kernel occupancy / regs / smem / DRAM-BW / arithmetic intensity / warp stalls	ncu	this skill
c=1 decode-step budget (GPU-busy vs host-gap) + kernel-vs-host-vs-comm verdict	vLLM profiler endpoint / nsys	inference-decode-step-budget

Sequencing note: for the decode/latency tier, run inference-decode-step-budget FIRST. If at c=1 it returns "host-bound" (GPU idle >> busy per step, as GLM-5.1 does), per-kernel SoL is moot - the kernels are a small fraction of TPOT and are launch-latency-scale at one token. Only escalate to this skill when the budget says kernel-bound, or for the prefill/throughput tier.

When to use

• Investigating WHY a specific kernel is hot. The zymtrace-anchored-query
  • inference-kernel-profile skills tell you WHICH kernels are hot and HOW LONG they take. Ncu tells you whether they're memory-bound vs compute-bound, whether occupancy is the ceiling, whether warps are stalling on memory or sync, etc.
• Roofline analysis to prove a kernel is at-the-roof vs has-room.
• Pre-PR-submission justification: when proposing a custom kernel or a kernel-tuning change, ncu evidence (e.g. "this kernel achieves only 47% theoretical occupancy due to register pressure") is the kind of argument upstream reviewers expect.

Do not use this skill for:

• Continuous always-on capture - kernel replay is 10-100x slow per replayed kernel. Ncu is a per-shot tool.
• Untargeted "give me everything" sweeps - without --kernel-name scoping, ncu will replay EVERY kernel, which on a busy vLLM pod is a heavy operation that risks Kubelet liveness-probe failures.
• Multi-pod fleet capture - this skill targets ONE pod at a time.

Sidecar image

Same image as inference-kernel-profile: ghcr.io/cfregly/nsys-sidecar:0.1.0 (publicly readable). Image includes nsys 2025.6.3 + ncu 2026.1.1 + py-spy 0.4.1 + python3 + jq.

Image is 11.87 GB. First-pull on a new GPU node is ~3-7 min from ghcr.io. Subsequent attaches on the same node are instant.

Safety: live-serving impact

ncu's --set full capture flag enables every hardware-counter group, which forces kernel replay (the kernel is launched, ncu reads the counters, the kernel is launched AGAIN, ncu reads the next group, ...). Replay multiplies the kernel's wall-clock by 10-100x.

On a single-replica deploy, the replay slowdown can spike pod CPU to the point of Kubelet liveness-probe failure. Mitigate by:

• Using --launch-count 3 not 5
• Using --set basic instead of --set full for the first capture (basic captures only the metric groups required for roofline, ~3x slowdown instead of 30x)
• Scoping to ONE kernel per capture, not 5

On a multi-replica deploy, a temporary per-replica capacity dip during ncu replay is usually acceptable, so --launch-count 5 + --set full is safe - the slow replica is just 1 of N and the Service load-balancer distributes around it.

Fallback: if even the conservative path is too risky, spin a sister deploy <deploy>-ncu at 0 service routing (a separate Helm release serving the same model, NOT in the Service selector), and ncu against THAT pod. Adds ~30 min for the sister helm install, but zero risk to production serving.

Memory caveat: at gpu-mem-util >= 0.85 there is little headroom for a profiler's host/device buffers. A long capture window (observed with a 40s nsys window on a GLM-5.1 canary) can OOM-crash vllm mid-capture and truncate the report. Keep windows short, scope ncu to one kernel + low --launch-count, and prefer the endpoint-triggered bounded windows in inference-decode-step-budget.

Gate 0 (precondition): CUPTI must even initialize (CUDA image-vs-driver skew)

ncu is a CUPTI client, so on GB300 nodes it can record 0 kernels for the same reason nsys + the vLLM torch profiler do: a CUDA 12.9 serve image against the node's CUDA 13.0 driver makes CUPTI fail to init (CUPTI_ERROR_INVALID_DEVICE). This is NOT permission (RmProfilingAdminOnly:0), NOT a missing lib (libcupti.so.12 present + linked), and NOT a wrong-process attach - it is a CUDA major-version toolkit-vs-driver skew. If ncu returns 0 kernels, grep the launch log for CUDA versions. CUPTI/Runtime/Driver: a 12.x-toolkit / 13.x-driver split needs a CUDA-13-aligned image or zymtrace (non-CUPTI), not more attach tuning.

SOLVED PATH (GB300 default): pull a Blackwell-capable ncu from NGC instead of using the in-image ncu: copy ncu 2026.x from nvcr.io/nvidia/pytorch:26.05-py3 (arm64/sbsa) into the serve container via an initContainer (no prod rebuild. Needs an NGC image-pull secret in the namespace). Use this NGC-tools path on GB300 for both nsys and ncu, the legacy in-image / apt paths are superseded there. Verified end-to-end on a GB300 MoE deploy (per-kernel Compute(SM)/Occupancy resolved).

ncu capture-hygiene (empty-rep / non-deterministic gates) - empty != tooling limit

Beyond Gate 0 (CUPTI), three ncu traps on a vLLM stack each yield "No kernels were profiled" or a non-deterministic-count failure. NONE is a tooling limit (each reproduced + fixed on a DeepSeek-V4-Flash GB300 deploy). Canon: docs/METHODOLOGY.md "Capture hygiene".

1. cudaProfilerStart breaks under any vLLM direct_register_custom_op import. If your harness imports a module that runs direct_register_custom_op at load (mhc.tilelang, fp8_utils, …), ncu --profile-from-start off + an in-script torch.cuda.cudart().cudaProfilerStart() captures 0 kernels (the custom-op/triton registration perturbs the CUPTI profiler-start hook). FIX: do NOT rely on cudaProfilerStart - profile from start and exclude warmup with --launch-skip <warmup> --launch-count N + --kernel-name scoping:

   M=256 N=4096 K=8192 ncu --kernel-name 'regex:sm100_fp8_fp4_gemm' \
     --launch-skip 3 --launch-count 1 --set full --target-processes application-only \
     --export out -- python3 one_op.py     # one_op.py warms the op 3x then loops; ncu skips the 3 warmups
   

2. -- env VAR=v python3 defeats --target-processes application-only - ncu profiles the env process, not its python child → 0 kernels. FIX: set the env on the ncu process itself (VAR=v ncu … -- python3 …), never via an env wrapper after --.
3. TP=N MoE+sparse in-engine --replay-mode application is non-deterministic. A large MoE + sparse-attention model relaunched per metric-pass varies its kernel-launch count → ==ERROR== Unexpected number of profiled kernels, --app-replay-mode relaxed + no-op profile_run + prefix-caching-off + eager + fixed-blocks do NOT fix it. The canonical L4 path is an isolated single-op kernel-replay harness: call the production library op directly (e.g. vllm.utils.deep_gemm.fp8_gemm_nt / tf32_hc_prenorm_gemm), TP=1, NO mhc.tilelang import, synthetic fixed-shape inputs (AI/%SoL is shape-structural). Mirror the production caller's quant + SF layout (e.g. per_token_group_quant_fp8 + per_block_cast_to_fp8 + deepgemm_post_process_fp8_weight_block) so the exact kernel template fires.

Two blockers on prod-direct attach

An older ncu --attach <PID> recipe attached ncu to a running vllm process directly. That recipe is broken on current production deploys for two independent reasons. Read this section before attempting any live capture.

Blocker 1: zymtrace already owns CUDA_INJECTION64_PATH

Production vllm deploys instrumented with zymtrace run with:

CUDA_INJECTION64_PATH=/var/lib/zymtrace/profiler/libzymtracecudaprofiler.so

This is the zymtrace profiler agent injecting itself as the CUDA driver-level injection library. The CUDA driver only honors one injection library per process. Ncu cannot stack on top. There's no way to add ncu's libcompute.so to a running zymtrace-instrumented process.

Exception: latency/canary deploys often have NO zymtrace injection. A canary that runs with no CUDA_INJECTION64_PATH in its env escapes Blocker 1 - ncu launch-mode (or the preload+TCP attach below) works directly on it without a separate sister-deploy. Check the target's env (kubectl get deploy <name> -o jsonpath='{...env...}') before assuming a sister is required. The sister-deploy is only mandatory for the zymtrace-instrumented production releases.

Blocker 2: ncu 2026.1.1 dropped --attach <PID>

The deprecated --attach <PID> flag was removed in ncu 2026.x:

==ERROR== unrecognised option '--attach'. Use --help for further details.

The modern ncu interaction modes (per ncu --help) are:

• --mode launch-and-attach (default) - wrap the application at process startup
• --mode launch - launch the application and suspend for a later attach
• --mode attach - connect to a process pre-instrumented with ncu's injection library, via TCP (--hostname + --port)

The only path that works against an already-running vllm process is --mode attach, and it requires NV_NCU_INJECTION64_PATH to have been set when vllm started so the process exposes the ncu profiling endpoint. Production vllm (instrumented with zymtrace instead) does not expose this endpoint.

Recipe: sister-deploy with preload + TCP attach

Both blockers are dodged by spinning up a parallel sister-deploy helm release running the same vllm image but with:

• zymtrace CUDA_INJECTION64_PATH unset
• NV_NCU_INJECTION64_PATH pointing at ncu's libcompute.so (mounted from the nsys-sidecar image via an initContainer + emptyDir volume)
• replicas: 1
• a Service selector / label that excludes prod traffic (the prod Service matches app: basic-inference, the sister uses app: basic-inference-ncu, so prod LB routes around it)

The vllm process on the sister pod exposes ncu's TCP profiling endpoint on 127.0.0.1:49152. From a kubectl debug sidecar with --share-processes, run:

ncu --mode attach --hostname 127.0.0.1 --port 49152 \
    --kernel-name '<KERNEL_REGEX>' \
    --launch-count 5 \
    --set full \
    --target-processes all \
    --export /profiling/ncu-$K.ncu-rep

Multiple captures against the same long-lived sister pod are supported - vllm stays warm. The sidecar runs ncu N times sequentially.

Reference helm + capture scaffolding

A reusable sister-deploy scaffold (one directory per model) contains:

• values-ncu-sister.yaml - helm values overrides
• install.sh - helm upgrade --install wrapper
• capture.sh - full capture flow (wait-ready, warmup, sidecar attach, N-kernel loop, extract, helm uninstall). Flags: --launch-count N, --set basic|full, --roofline-min (AI-roofline --metrics set only), --replay-mode kernel|application|range, and --campaign <slug> --cell-id <cell> to auto-import the result into a perf-report campaign cell.
• README.md - runbook + canonical 5-kernel list
• a replay-mode-application runbook - the ack-gated path past the TP=8 NVFP4 ContextSaveFailed kernel-replay blocker (use --replay-mode application --roofline-min).

Identifying hot kernels

ncu --kernel-name accepts substring or regex match against the demangled or mangled kernel name. Demangle a mangled symbol via c++filt (available in the nsys-sidecar image):

echo "_ZN66_GLOBAL__N__51f43292_25_CUDASymmetricMemoryOps_cu_c81adf72_277485226multimem_all_reduce_kernelIN3c108BFloat16ELi16EEEvPT_mPPjmm" | c++filt
# -> (anonymous namespace)::multimem_all_reduce_kernel<c10::BFloat16, 16>(...)

Either form is fine for --kernel-name:

--kernel-name multimem_all_reduce_kernel
--kernel-name "regex:multimem_all_reduce.*BFloat16"

Canonical 5-kernel set for B200 NVFP4 inference (Kimi K2.6, GLM-5.1, DeepSeek):

Kernel substring	Category	Expected bottleneck
multimem_all_reduce_kernel	NCCL	NVLink5 bandwidth
bmm_E2m1	BMM-NVFP4	NVFP4 Tensor Core compute
fmhaSm100fKernel	FMHA	HBM3e bandwidth
nvjet_tst_.*_2cta	MoE / GEMM	NVFP4 Tensor Core compute
triton_red_fused	Triton-fused	Mixed

Recipe (deprecated - DO NOT USE on prod-direct)

An earlier recipe used ncu --attach $VLLM_PID against the zymtrace-instrumented production pod. That recipe is preserved below ONLY as historical reference. It WILL FAIL on every current inference deploy. Use the sister-deploy section above.

Historical recipe (broken. Click to expand)

# THIS WILL FAIL:
# ERROR: unrecognised option '--attach'  (ncu 2026.1.1)
# ERROR: CUDA injection slot taken by zymtrace
ncu --kernel-name '$KERNEL' --launch-count 5 --set full \
    --export /profiling/ncu-$KERNEL.ncu-rep \
    --attach $VLLM_PID

5. Export human-readable CSV

kubectl -n $NS exec $TARGET_POD -c $SIDECAR -- bash -c "
  ncu --import /profiling/ncu-${KERNEL}.ncu-rep \
    --csv --page raw > /profiling/ncu-${KERNEL}-raw.csv
  ncu --import /profiling/ncu-${KERNEL}.ncu-rep \
    --csv --page details --section SpeedOfLight \
    > /profiling/ncu-${KERNEL}-sol.csv
"

Key columns from --page details --section SpeedOfLight:

Column	Meaning
Memory Throughput [%]	DRAM throughput vs theoretical peak
DRAM Throughput [%]	Same, restricted to DRAM (vs L2)
Compute (SM) Throughput [%]	SM utilization
Achieved Occupancy	Actual warps-active / theoretical-max-warps-active
Theoretical Occupancy	What the kernel COULD achieve given regs+smem
Achieved Active Warps Per SM	Average warps active per SM
Block Limit Registers	Limit imposed by registers/thread
Block Limit Shared Mem	Limit imposed by smem/block
Block Limit Warps	Limit imposed by max warps per SM

These are the roofline + occupancy diagnostics. A kernel with DRAM Throughput % = 92% is memory-bound. One with Compute SM Throughput % = 88% is compute-bound. One with Achieved Occupancy = 0.31 and Block Limit Registers = limited is suffering register pressure.

6. Extract artifacts

BUNDLE=experiments/artifacts/inference-perf-bench/<bundle>/
mkdir -p $BUNDLE/ncu-profiles
for kernel in multimem_all_reduce_kernel flashinfer_trtllm_allreduce_fusion fmhaSm100fKernel concat_and_cache_mla_kernel bmm_E2m1; do
  kubectl -n $NS cp $TARGET_POD:/profiling/ncu-${kernel}.ncu-rep $BUNDLE/ncu-profiles/ -c $SIDECAR
  kubectl -n $NS cp $TARGET_POD:/profiling/ncu-${kernel}-sol.csv $BUNDLE/ncu-profiles/ -c $SIDECAR
done

7. Populate kernel_internals field in inference_perfbench_v1.json

import json, csv, pathlib
bundle = pathlib.Path("$BUNDLE")
ipb = json.loads((bundle / "inference_perfbench_v1.json").read_text())
ipb["kernel_internals"] = {
    "captured_at": "<UTC>",
    "method": "ncu-sidecar-kernel-scoped",
    "sidecar_image": "ghcr.io/cfregly/nsys-sidecar:0.1.0",
    "vllm_pid": $VLLM_PID,
    "per_kernel": {
        # one entry per kernel captured:
        # "<kernel-name>": {
        #     "achieved_occupancy_pct": ...,
        #     "theoretical_occupancy_pct": ...,
        #     "dram_throughput_pct_peak": ...,
        #     "sm_throughput_pct_peak": ...,
        #     "regs_per_thread": ...,
        #     "smem_per_block_bytes": ...,
        #     "block_limit_factor": "registers" | "shared_mem" | "warps",
        # }
    },
}
(bundle / "inference_perfbench_v1.json").write_text(json.dumps(ipb, indent=2))

The inference_perfbench_v1 schema treats kernel_internals as optional - bundles without it are unaffected.

8. Cleanup

kubectl -n $NS exec $TARGET_POD -c $SIDECAR -- rm -rf /profiling/ncu-*
# The sidecar container will terminate after the 3600s sleep; pod
# auto-cleans the ephemeral container.

Cross-skill join

Roofline interpretation is most useful when joined with the absolute kernel-time from inference-kernel-profile (nsys) and the relative sample-share from zymtrace-anchored-query. Example join:

Kernel                                  zymtrace samples %  nsys total ms  ncu DRAM %  ncu SM %  Verdict
flashinfer trtllm_allreduce_fusion      14.2%               1,847          88%          12%      Memory-bound; comm-bound (good - kernel is at-the-roof)
fmhaSm100fKernel...Persistent           8.7%                1,144          47%          81%      Compute-bound (room for compute-side tuning)
multimem_all_reduce_kernel              5.3%                694            91%           9%      Memory-bound; comm-bound (at-the-roof)
bmm_E2m1_E2m1E2m1                       6.9%                901            61%          74%      Mixed (canonical NVFP4 BMM: balanced)

Without ncu, you have shares (zymtrace) + times (nsys) but no attribution to the dimension (memory vs compute vs occupancy). ncu closes that loop.

Cost + risk

• ~10-100x per-replayed-kernel slowdown during capture. Bounded by --launch-count (5 replays at 100x = 0.5s of kernel time = sub-second for typical kernels)
• ncu-rep files are typically 5-50 MB per kernel (manageable)
• Sidecar attach is non-disruptive (no vllm restart)
• Live-pod risk: see Safety section above

Pair this skill with evidence-bundle-init when starting a new investigation so the ncu-profiles/ subdir lands in the right place.

Full-context reporting (no bare numbers)

This skill is the preferred follow-up for the proper roofline scatter. Per the canon "Every performance number carries its full context (no bare numbers)" (docs/METHODOLOGY.md "Full-context reporting"): every number this skill emits MUST carry its full measurement-context descriptor, and every comparison MUST be matched on it. A bare number is a defect - it cannot set a default, ship a config, or appear in a report.

• Identity: model (+HF path), hardware (exact ceiling token GB300/B200), quant, kv-cache dtype.
• Parallelism: TP, DP (replicas), PP, EP, parallel_strategy.
• Serving cfg: max-num-seqs, max-num-batched-tokens, gpu-memory-utilization, max-model-len, cudagraph_mode/enforce_eager, async_scheduling, prefix-caching.
• Workload: dataset, ISL/OSL (or mean in/out tokens), concurrency, num-prompts.
• Regime: warm vs cold. Latency vs throughput tier.
• Stack: image/vllm commit, bench backend, serving engine.
• Grounding: %SoL (+ ceiling key from configs/sol-ceilings.yaml - never inline a peak), sol_rigor (L1-L4), trials n (mean±std), same-node, baseline named.
• Per-number exact shape (no smoothing): when reporting more than one number, keep EACH with its own exact shape (ISL/OSL, concurrency, dataset, regime) - never normalize a set to one uniform descriptor that hides per-point variation (e.g. c=1 @ ISL1024/OSL256 + c=64 @ ISL4096/OSL512, NOT one shared "random").

This skill is the preferred path to a real per-kernel arithmetic-intensity-vs-roofline scatter plot per docs/METHODOLOGY.md "Speed-of-light framing". The other two siblings (zymtrace-anchored-query, inference-kernel-profile) deliver time-share + wall-clock duration but cannot compute %SoL per kernel because they lack the FLOPS + bytes counters this skill captures (sm__sass_thread_inst_executed_op_*_pred_on.sum, dram__bytes.sum).

Workflow when proper %SoL is needed:

1. Identify the dominant hot kernel via zymtrace-anchored-query + inference-kernel-profile.
2. Run THIS skill against that kernel name with the roofline-min counter set (see Reference below).
3. Compute arithmetic intensity = FLOPS / bytes. Place the point on the B200 / GB300 / H100 roofline using peaks from configs/sol-ceilings.yaml (b200_sm100.nvfp4_dense_pflops for compute ceiling, b200_sm100.hbm3e_tbps for bandwidth ceiling). Cite by key path, never inline magic numbers.
4. Record the resulting %SoL in the per-run sol-summary.md doc for the campaign / cluster probe this kernel came from.

Next lever / BREAKTHROUGH (Grind Mandate)

If this skill emits a measured result, its output MUST end by naming the next perf lever, its expected unlock (direction + rough magnitude), and the gate that proves/refutes it, per docs/METHODOLOGY.md "Always be grinding (next-lever framing)". A measured win is the new floor, not the finish -- so do everything we can to find the next BREAKTHROUGH: the highest-EV unlock toward Speed-of-Light (a new champion / kernel / router / quant / parallelism / spec-decode win, or an unblocked stack), not just the next micro-lever. Rank the candidate breakthrough levers by value x cost (the GRIND FRONTIER, perftunereport value_view), pursue the top, bank the rest with evidence. Record WHY a refuted lever loses, update the standing frontier in the active bundle's HANDOFF.md. Never conclude "exhausted/optimal/done" without an explicit next-lever frontier (an empty frontier AND a documented SoL wall only). Delete this section ONLY if the skill produces no measurements.

Wiring ncu into the perf-report page-5 roofline scatter

The capture's ncu-profiles/*-sol.csv + *-raw.csv are ingested into a perf-report campaign cell as cells/<cell-id>/ncu_kernels.json (the page-5 input) via the import_ncu verb:

perftunereport import_ncu --campaign <slug> --cell-id <cell-id> --bundle <bundle-dir>
perftunereport report_render --campaign <slug>   # -> page 5 populated

(capture.sh --campaign <slug> --cell-id <cell> runs this automatically at the end.) Notes:

• Two CSV shapes are auto-handled. ncu's --page raw is wide (one row per kernel, metric columns). Ncu-2026's --page details --section SpeedOfLight is long/melted (Metric Name / Metric Value rows). The importer detects and pivots the long shape, so either export works.
• Counter set determines what page 5 can show. --set=full or --roofline-min collect dram__bytes.sum + the sm__sass_thread_inst_executed_op_*_pred_on.sum FLOP op-counts, so the importer computes arithmetic intensity + achieved TFLOPS and page 5 plots a real roofline point. --set=basic collects neither, so AI is null and page 5 renders a hollow "%SoL only / AI unmeasured" marker placed at SM% x the kernel family's compute ceiling (category_ceiling_map in configs/sol-ceilings.yaml) - the y is honest, the x is a placeholder. AI is never fabricated.
• SM-busy% is NOT %-of-FLOP-SoL - never conclude "at-roof" from --set basic. The --set basic sm__throughput.avg.pct_of_peak ("SM busy") can read 88-92% while the kernel is at <15% of its FLOP-roofline - a persistent / split-K / spinning kernel keeps SMs busy doing little tensor work. To decide at-roof vs headroom you MUST run --set full and compare achieved TFLOPS to the FLOP ceiling (fp8_dense_pflops / nvfp4_dense_pflops / bf16_dense_pflops). WORKED EXAMPLE: the DeepSeek-V4-Flash FP8 GEMM (sm100_fp8_fp4_gemm_1d1d, ~70% of decode compute) read 88-92% SM (--set basic, which mislabeled it "at-roof") but --set full showed only 1-14.5% of the FP8 FLOP-SoL (M=1→256) - the kernel is concurrency-starved, not exhausted. The throughput tier was the real headroom, not a kernel rewrite.
• TP=8 NVFP4 blocker. Multi-pass kernel-replay fails at TP=8 NVFP4 (ContextSaveFailed). See the replay-mode-application runbook in the sister-deploy scaffolding above for the --replay-mode application path that gets to a full AI-grounded point.

Kernel rubric (K/R/H/P/A) - this skill is the H + P enforcement point

When this capture backs a custom-kernel comparison (a candidate kernel vs a baseline), apply the kernel rubric (see docs/METHODOLOGY.md "Kernel-work classification"). ncu is the only profiler in the sibling set that can prove the two axes a kernel win actually turns on:

• H (hardware specialization) - the Compute (SM) Throughput [%] and tensor-pipe active % (from the SpeedOfLight section) reveal whether a kernel engages the frontier path. On SM100 the production libraries are H4 (sm100f tensor cores / NVFP4 tensor cores via bmm_E2m1, nvjet_tst_* in the canonical 5-kernel set). A candidate kernel that shows near-zero tensor-pipe activity / SM% dominated by FMA is H1 - and an H1 candidate cannot beat an H3-H4 baseline on a K3-K4 op no matter how it schedules. Read tensor-core engagement off ncu BEFORE believing any win.
• P (performance target) - the roofline (%SoL via the FLOPS + dram__bytes.sum counters, "Speed-of-light reporting" above) is the P-axis: P4 means at/above the best library. A kernel far below its family ceiling that still "wins" an e2e A/B is winning on something other than GPU work (re-check methodology).

The gate, operationally: record (K,R,H,P,A) for the candidate AND the named baseline in the bundle's SOURCE.md/summary.md. A speedup over a baseline at strictly lower H or R (e.g. a tensor-core candidate vs a generic-Triton baseline when production runs the sm100f library) is a DRAFT, never a VERDICT - it fails the "Fair baseline" clause. The canonical worked failure: warp-decode (K4/R2/H1) beat generic Triton in microbench but ncu/zymtrace confirmed it never engaged tensor cores, and it lost 1.51x to FlashInfer-TRTLLM (K4/R1/H4) on real GPU time.

Emit it as a structured krhpa: block (not just prose). When the campaign renders an L4 ncu roofline (page 5, sol_rigor=L4), perftunereport publish_to_lake FAILS CLOSED unless the campaign config.yaml carries a krhpa: block classifying both arms - prose in SOURCE.md/summary.md alone does not satisfy the gate for an L4 campaign. Add to the campaign config:

krhpa:
  candidate: {K: 4, R: 2, H: 1, P: 2, A: 1, name: "warp-decode (Triton FMA)"}
  baseline:  {K: 4, R: 1, H: 4, P: 4, A: 1, name: "FlashInfer-TRTLLM bmm_*_sm100f"}

Each axis is an int 1..4 (= L1..L4), baseline.name must name the production-representative kernel/library. The gate (lake_writer.krhpa_problems) refuses a missing or malformed block under --strict and records + warns otherwise.

Reference: full hardware-counter set names

ncu's --set full enables ~60 metric groups. For roofline analysis the minimum set is:

sm__sass_thread_inst_executed_op_*_pred_on.sum  (per-op work counts)
dram__bytes.sum                                  (DRAM bytes read+written)
gpc__cycles_elapsed.max                          (peak cycles)
smsp__warps_active.avg.pct_of_peak_sustained_active  (occupancy)
launch__registers_per_thread                     (regs/thread)
launch__shared_mem_per_block_static              (smem/block)

These are also available under the named section group --section SpeedOfLight_HierarchicalTensorRooflineChart for direct roofline plotting.