bisect-precision

name	bisect-precision
description	Locate which pypto commit introduced a precision regression. Only pypto and its corresponding simpler (submodule) are tracked — ptoas and pto-isa versions are not part of the bisect. If the culprit is a simpler submodule bump, performs a second-level bisect within simpler.

Bisect Precision Regression

Locate the exact commit that introduced a precision regression in a pypto-lib example by binary-searching through pypto history. Simpler (runtime) is a git submodule of pypto, so each pypto commit also pins a specific simpler version. This skill only tracks pypto + simpler — ptoas and pto-isa are assumed stable and are NOT bisected, even if pypto's CI config references newer versions.

Repository Layout

Component	Path	How it's tracked
pypto (compiler)	<pypto_dir>	Independent repo — the first-level bisect target
simpler (runtime)	<pypto_dir>/runtime	Git submodule of pypto — the second-level bisect target (only if needed)
ptoas (assembler)	external binary	Not tracked by this skill. Assumed stable at the currently installed version.
pto-isa	instruction set definitions	Not tracked by this skill. Assumed stable at the currently installed version.

Typical absolute paths:

/data/<user>/newpto/pypto          ← pypto repo root
/data/<user>/newpto/pypto/runtime  ← simpler (submodule)
/data/<user>/newpto/pypto-lib      ← this library

Prerequisites

• The example script must have been passing before and is now failing precision.
• The user knows (or MEMORY.md records) a known-good pypto commit. If not available, ask the user. A known-good simpler commit is not required — it is derived automatically from pypto's submodule pointer.
• The example must be runnable via python <script> -p <platform> -d <device>.
• pypto repo is locally available.

Workflow

Phase 0: Gather Context

1. Ask the user which example script is failing (if not already clear).
2. Read memory/MEMORY.md for a known-good pypto commit. If none recorded, ask the user.
3. Determine repo paths:

   PYPTO_DIR=$(cd ../../pypto && pwd)
   SIMPLER_DIR=$PYPTO_DIR/runtime
   

4. Record the current HEAD of pypto as the known-bad commit:

   PYPTO_BAD=$(git -C $PYPTO_DIR rev-parse HEAD)
   

5. Determine the run command. Typical pattern:

   source run.sh  # or manually export env vars
   python models/qwen3/<script>.py -p a2a3 -d <device>
   

Phase 1: Triage — Compiler vs Runtime (Optional Quick Check)

Compare the generated code from a known-good build against the current (bad) build to get an early signal on whether the regression is in codegen or runtime.

Step 1a: Generate a good build output (if needed)

# Save current state
PYPTO_BAD=$(git -C $PYPTO_DIR rev-parse HEAD)

# Checkout known-good pypto commit (this also sets the submodule pointer)
git -C $PYPTO_DIR checkout <pypto_good_commit>
git -C $PYPTO_DIR submodule update --init runtime
pip install --no-build-isolation -e $PYPTO_DIR
pip install --no-build-isolation -e $SIMPLER_DIR

# Run the example to generate a good build_output
python <script> -p <platform> -d <device>
GOOD_BUILD=$(ls -td build_output/<ProgramName>_* | head -1)

# Restore
git -C $PYPTO_DIR checkout $PYPTO_BAD
git -C $PYPTO_DIR submodule update --init runtime
pip install --no-build-isolation -e $PYPTO_DIR
pip install --no-build-isolation -e $SIMPLER_DIR

Step 1b: Diff generated code

diff -rq $GOOD_BUILD/kernels/      $BAD_BUILD/kernels/
diff -rq $GOOD_BUILD/ptoas/        $BAD_BUILD/ptoas/
diff -rq $GOOD_BUILD/orchestration/ $BAD_BUILD/orchestration/

Interpretation (informational only — bisect always starts with pypto):

Diff result	Meaning
Files differ in kernels/, ptoas/, or orchestration/	Compiler (pypto) generated different code — likely a pypto code change
No differences (only timestamps / .o binaries)	Same generated code — likely a simpler (runtime) change via submodule bump

Report the triage result to the user before proceeding. This does not change the bisect strategy (always bisect pypto first), but helps set expectations.

Phase 2: First-Level Bisect — pypto

Determine bisect parameters

GOOD_COMMIT=<pypto_known_good>
BAD_COMMIT=$PYPTO_BAD

# Count commits in range
git -C $PYPTO_DIR log --oneline $GOOD_COMMIT..$BAD_COMMIT | wc -l

Report the commit count to the user (~log2(N) bisect steps).

Run the bisect

cd $PYPTO_DIR
git bisect start
git bisect bad $BAD_COMMIT
git bisect good $GOOD_COMMIT

For each bisect step:

1. Sync submodule and install:

   git -C $PYPTO_DIR submodule update --init runtime
   pip install --no-build-isolation -e $PYPTO_DIR
   pip install --no-build-isolation -e $SIMPLER_DIR
   

   If install fails (e.g. incompatible API change), mark as skip:

   git bisect skip
   

2. Run the example:

   cd <pypto_lib_dir>
   python <script> -p <platform> -d <device>
   

3. Check result:

   • If output contains PASS → cd $PYPTO_DIR && git bisect good
   • If output contains FAIL or non-zero exit → cd $PYPTO_DIR && git bisect bad
   • If crash / unrelated error → cd $PYPTO_DIR && git bisect skip

4. Report progress to the user after each step:

   Step N/~M: <commit_short> — <commit_message> → good/bad/skip
   

5. Repeat until git bisect identifies the first bad commit.

Bisect complete

CULPRIT=$(git -C $PYPTO_DIR bisect view --oneline)
git -C $PYPTO_DIR bisect reset

Evaluate the culprit

Check whether the first bad commit is a submodule bump (i.e. it only changes the runtime/ submodule pointer):

git -C $PYPTO_DIR show <culprit> --stat

• If the commit touches only runtime (submodule pointer change), or the commit message matches patterns like chore(runtime): bump simpler, proceed to Phase 2b (second-level bisect in simpler).
• Otherwise, the regression is in pypto itself — skip to Phase 3.

Phase 2b: Second-Level Bisect — simpler (only if needed)

This phase runs only when the first-level bisect identified a submodule bump commit as the culprit. The regression is somewhere in the simpler commits between the old and new submodule pointers.

Determine simpler bisect range

# The culprit pypto commit bumped runtime/ from OLD_PTR to NEW_PTR
# Get the submodule pointer BEFORE the culprit (the good simpler version)
SIMPLER_GOOD=$(git -C $PYPTO_DIR show <culprit>^:runtime | head -1)
# If the above doesn't work, use:
SIMPLER_GOOD=$(git -C $PYPTO_DIR rev-parse <culprit>^:runtime)

# Get the submodule pointer AT the culprit (the bad simpler version)
SIMPLER_BAD=$(git -C $PYPTO_DIR rev-parse <culprit>:runtime)

# Pin pypto at the culprit commit (the compiler code didn't change)
git -C $PYPTO_DIR checkout <culprit>
pip install --no-build-isolation -e $PYPTO_DIR

# Count simpler commits in range
git -C $SIMPLER_DIR log --oneline $SIMPLER_GOOD..$SIMPLER_BAD | wc -l

Report the simpler commit range to the user.

Run the simpler bisect

cd $SIMPLER_DIR
git bisect start
git bisect bad $SIMPLER_BAD
git bisect good $SIMPLER_GOOD

For each bisect step:

1. Install:

   pip install --no-build-isolation -e $SIMPLER_DIR
   

2. Run the example:

   cd <pypto_lib_dir>
   python <script> -p <platform> -d <device>
   

3. Check result and mark (same as first-level: PASS → good, FAIL → bad, crash → skip).

4. Report progress after each step.

5. Repeat until bisect identifies the first bad simpler commit.

Simpler bisect complete

SIMPLER_CULPRIT=$(git -C $SIMPLER_DIR bisect view --oneline)
git -C $SIMPLER_DIR bisect reset

Phase 3: Report

Present to the user:

1. Regression source: compiler (pypto) or runtime (simpler).
2. First bad commit: hash, message, author, date.
   • If second-level bisect was performed, report both the pypto submodule bump commit and the specific simpler commit.
3. What changed: git show <commit> --stat summary.
4. Diff highlights: key changes that likely affect precision (look for dtype changes, cast operations, memory layout changes, optimization pass changes).
5. Restore state: confirm pypto is back to its original HEAD.

# Restore pypto to original HEAD (submodule follows automatically)
git -C $PYPTO_DIR checkout $PYPTO_BAD
git -C $PYPTO_DIR submodule update --init runtime
pip install --no-build-isolation -e $PYPTO_DIR
pip install --no-build-isolation -e $SIMPLER_DIR

Important Notes

• Always restore pypto to its original HEAD after bisect, regardless of outcome. Use git submodule update --init runtime to sync simpler back.
• Each pypto checkout changes the submodule pointer — always run git submodule update --init runtime after each checkout to keep simpler in sync. This is the key simplification: no manual simpler pinning needed.
• Each pip install of pypto takes ~30s-2min (C++ recompilation). Simpler is similar. Factor this into time expectations.
• Environment variables: make sure PTOAS_ROOT, PTO_ISA_ROOT, ASCEND_HOME_PATH, and runtime pool sizes (PTO2_RING_*) are set. Check run.sh in the project root.
• Build output comparison ignores .o / .so files (binary artifacts) — only compare .cpp and .pto source files.
• If the example uses --clear-cache, include that flag during bisect to avoid stale cached data affecting results.
• If pip install fails on a specific commit (e.g., API breaking change), use git bisect skip — git will try adjacent commits.

Asking the User

At any point, if information is missing:

Missing info	What to ask
Known-good pypto commit	"What is the last pypto commit where precision was passing?"
Which build_output is good	"Which build_output timestamp was from a passing run?"
Platform / device	"Which platform and device ID should I use? (e.g., -p a2a3 -d 5)"
Script to run	"Which example script is failing? (e.g., qwen3_14b_prefill.py)"