Datasets:

Alexsssu
/

fastkernels-b200-codex-vanilla-20260923

Unlike a version-ablation study there is no second leg here, so this stack is a description rather than an independent variable: both the baseline and the candidate run inside it, and every speedup is a within-stack ratio.

Code

repo	commit	local changes
`Snowflake-AI-Research/fastkernels`	`9acebaa`	none -- verified clean checkout
`sfc-gh-goliaro/vanilla-agents-fastkernels`	`0a05814`	one, `scripts/run.sh`, shipped as `patches/run.sh.patch`

The FastKernels checkout being unmodified matters: the baselines the agent is scored against, the tolerance checker, and the bench harness are all stock. It was cloned fresh for this experiment specifically to keep it that way, separate from the working copy used for an unrelated vLLM study on the same node.

Agent


CLI	`codex-cli` 0.156.1, prebuilt `x86_64-unknown-linux-musl` binary from the GitHub release
model	`openai-gpt-5.6-sol`
reasoning effort	high
API	Snowflake Cortex (Snowhouse), `responses` wire API
invocation	`codex exec --yolo --skip-git-repo-check -m openai-gpt-5.6-sol`
prompt	stock `prompts/optimize.md` from the harness, unmodified

The model id deviates from the harness default and this matters for comparability. run.sh defaults to -m openai-gpt-5.6-sol:high. The Cortex endpoint rejects that with unknown model; only the bare openai-gpt-5.6-sol resolves. The :high suffix was therefore moved out of the model id and into model_reasoning_effort = "high" in patches/codex-config.toml, which the CLI reports back as reasoning effort: high at session start. The intent is the same; the mechanism is not the harness default.

Three further pieces of codex configuration were needed to reach Cortex at all, all in patches/codex-config.toml:

a custom model_provider, because codex 0.156.1 ignores OPENAI_BASE_URL, which is the only thing run.sh sets. Without this every request goes to api.openai.com and 401s.
model_catalog_json, pointing at a catalog entry for openai-gpt-5.6-sol. Absent metadata makes codex fall back to defaults that enable the web-search tool, which Cortex rejects outright.
web_search = "disabled" -- a top-level enum, not the [tools] web_search boolean, which is accepted by the config parser but has no effect here.

Harness settings

Stock defaults except where noted.

setting	value	source
mode	`all` (independent, then sequential, then compare)	default
targets	every L1-L3 operator in the default capture: 133	default
levels	1,2,3	default
concurrent agent sessions	12	default `MAX_AGENT`
session timeout	5 h	default `AGENT_TIMEOUT`
GPU lease timeout	15 min	default `BENCH_TIMEOUT`
winner gate	every non-skipped scenario `PASSED` and geomean >= 1.0	default
`FK_DIR`	the clean fastkernels checkout	set explicitly
`AGENT_ARGS`	overridden, see above	not default

Agents do not hold a GPU while thinking; they lease one through with_gpu.py only to run validate.py, ncu or nsys.

Captured inputs

Shapes and dtypes come from captures/default/b200 in sfc-gh-goliaro/fastkernels-results, downloaded by the harness on first run. Its own provenance is capture_20260821-081742. These are recorded from real model executions, not synthesised, which is the point of the capture mechanism for data-dependent operators such as MoE routing.

Credentials

The Cortex token has an 18 h lifetime and was rotated once mid-run, at 2026-09-23 18:24 UTC, between the sequential agent phase and the final scoring. run.sh re-reads $HOME/.snowhouse-pat before every agent session, so no restart was needed and no session ran with an expired token. No 401s appear in any driver log.

Archive contents

path	what it is
`REPORT.md`	the analysis; `README.md` is generated from it
`CANONICAL.md`	which of the three scoring executions is authoritative, and where the artifacts are not self-consistent
`MANIFEST.md`	this file
`SOURCE_NOTES.md`	working documents that were deliberately not shipped, and why
`results/ind/`	standalone bench over all 133 merged candidates, the winner selection, per-target agent metrics
`results/comp/`	composed bench over the independent winners
`results/seq/`	composed bench over the sequential winners, plus the per-level mix benches and gating decisions
`results/compare.json`	the harness's own independent-vs-sequential comparison
`control/`	`fastkernels eval --self-test` on Llama-3.1-8B: the baseline-vs-baseline control that establishes the noise floor
`patches/`	the one harness change, the codex configuration, the scenario tables and driver scripts written for this run
`logs/`	the three driver logs
`logs-agents.tar.gz`	219 per-target codex session logs, 107 MB uncompressed
`make_tables.py`	regenerates every table in `REPORT.md` from `results/`
`make_card.py`	regenerates `README.md` from `REPORT.md`

The per-target agent workspaces (7,628 intermediate kernel snapshots, 5.8 GB) are not shipped here; see SOURCE_NOTES.md.

Local changes: `scripts/run.sh`

Two fixes, both required to get a complete run, both in patches/run.sh.patch. Neither touches measurement -- they only stop the driver from aborting.

1. fastkernels bench exiting non-zero aborts the driver. run_bench() called it bare under set -euo pipefail. Any failing candidate scenario makes the command exit 1, which killed the driver one line before winner selection. At 133 targets a clean sweep is not realistic, and the harness's own README calls the standalone bench "diagnostic only" -- the gate is applied afterwards by select_fk_winners.py reading the JSON. The fix distinguishes "some scenarios failed" from "the command crashed": if the output JSON exists, carry on. The same treatment is applied to run_e2e().

2. find ... | grep -q . misreports a large winner set as empty. Both run.sh:559 and :569 guard on ! find "$dir" -name '*.py' | grep -q .. grep -q exits at the first match and closes the pipe, find takes SIGPIPE, and under set -o pipefail the pipeline reports failure -- so 119 winners were read as zero and the composed bench and e2e were silently skipped. It does not trigger with a handful of winners, which is why the 5-target smoke run did not catch it. Replaced with [[ -z "$(find ... -print -quit)" ]], which stops find itself.

Both are worth upstreaming; the driver logs in logs/ are the evidence.

Manifest

Node

Runtime stack