Profile Isaac Sim Performance

Iterative profiling workflow: run a benchmark with GPU frame-time recording, capture a Tracy profile, export to CSV, compare against a reference, make changes, and repeat.

Prerequisites

All commands run from the release build directory:

cd _build/linux-x86_64/release

Asset root / Nucleus authentication

Benchmarks load scenes from an asset server. If OMNI_USER and OMNI_PASS are set, Nucleus authentication is automatic. Otherwise, add the S3 fallback flag to every benchmark invocation (after --) to skip interactive auth:

--/persistent/isaac/asset_root/default=https://omniverse-content-staging.s3-us-west-2.amazonaws.com/Assets/Isaac/6.0

ROS2 environment variables

Benchmarks that use ROS2 (e.g. robots_nova_carter_ros2) require these environment variables so the internal humble distro is found:

export ROS_DISTRO=humble
export RMW_IMPLEMENTATION=rmw_fastrtps_cpp
export LD_LIBRARY_PATH=$LD_LIBRARY_PATH:$(pwd)/exts/isaacsim.ros2.core/humble/lib

These are printed in the startup log by isaacsim.ros2.core if missing. Set them before running ./python.sh.

Step 1 — Validate User Request

When the user asks to profile a benchmark, check:

1. --gpu-frametime — must always be present. Add it if the user omitted it.
2. --num-frames — should be >= 100 for stable measurements (default in most benchmarks is 600, which is fine). If the user explicitly passes a low value like --num-frames 10, warn them and suggest at least 100.
3. Benchmark short name — resolve from the available set (see list below).

Available benchmarks (short names)

Benchmark scripts live in source/standalone_examples/benchmarks/.

Step 2 — Run Benchmark + Capture Tracy Profile + CSV

Use the Tracy capture wrapper to run the benchmark, record the Tracy profile, and export a CSV — all in one shot. The wrapper also saves the full benchmark stdout/stderr to a .log file, which contains the summary report metrics.

./python.sh tools/profiling/tracy_capture.py \
    --benchmark <short_name> \
    --output-dir /tmp/tracy_profiles \
    --csv \
    -- --gpu-frametime --num-frames <N> <extra-args>

Key flags:

• --csv — auto-export the tracy profile to CSV (tab-separated by default).
• --csv-sep <char> — column separator (default: \t). Tab avoids conflicts with commas in C++ zone names. When reading exported CSVs, always parse with sep='\t'.
• --csv-self — report self-times (useful for identifying hotspots).
• --capture-loading — include the scene-loading phase (omit to capture only the benchmark phase).
• --enable-python-profiling — adds Python function scopes (slower; use only when investigating Python-level bottlenecks).
• Everything after -- is forwarded to the benchmark script verbatim.

The output directory will contain:

• benchmark_<name>_<timestamp>.tracy (or .compressed.tracy)
• benchmark_<name>_<timestamp>.csv
• benchmark_<name>_<timestamp>.log (full stdout/stderr — includes the summary report)

Extract key metrics from the summary report at the end of the .log:

• Average frame time (ms)
• Min / Max frame time
• FPS (frames per second)
• GPU frame time stats (when --gpu-frametime is enabled)

Step 3 — Compare CSVs and Analyze

Zone-level comparison

Run the comparison script bundled with this skill (resolved via ${CLAUDE_SKILL_DIR}; falls back to the canonical repo path):

python3 "${CLAUDE_SKILL_DIR:-skills/profile-isaac-sim}/scripts/compare_tracy_csvs.py" \
    <reference.csv> <new.csv> --top 25

The script reads tab-separated Tracy CSV exports (the default from tracy_capture.py) and prints:

1. Top-N zones by total time in the reference, with the new run's mean and delta.
2. Zones that appear only in the new run (new hot paths).
3. Zones that disappeared from the new run.

Use --sep ',' if comparing older comma-separated exports.

Summary report comparison

Also extract key metrics from each run's .log file and present a side-by-side table:

Step 4 — Iterate

After sharing the analysis:

1. Explain findings — which zones dominate, what changed, hypotheses for why.
2. Propose a change — a specific code modification to improve performance.
3. Ask for user feedback — confirm the proposed change before implementing it.

After the user approves:

4. Implement the change.
5. Re-run the benchmark + capture (Step 2) with the exact same arguments.
6. Compare to both the original reference AND the previous iteration (Step 3) so progress is tracked across all iterations.
7. Present the updated comparison table with a new column for each iteration.

Repeat until the user is satisfied or no further gains are found.

Multi-iteration table format

Profiling Extension Unit Tests

When the user wants to profile a unit test (extension test) rather than a standalone benchmark, the test runner launches the actual kit process as a child, and Tracy must attach to that child process directly. Follow this workflow:

Step A — Discover the child process command

Run the test normally to capture the child process command line:

cd _build/linux-x86_64/release
./tests/tests-<extension>.sh -n <test_name> -f "<TestFilter>" 2>&1 | head -30

Look for the line starting with >>> running process: immediately after [EXTENSION TEST START: ...]. This is the full kit command with all --/ carb settings configured by the extension's extension.toml. Copy the entire command.

Example output:

||||||||||||||  [EXTENSION TEST START: isaacsim.sensors.rtx-enable_multitick_rendering]  ||||||||||||||
>>> running process: ./tests/../kit/kit .../omni.app.test_ext.kit --enable isaacsim.sensors.rtx-15.13.0 --/log/flushStandardStreamOutput=1 ... --/rtx/hydra/supportMultiTickRate=true

Step B — Kill the test and rerun with Tracy settings

Kill the running test process (Ctrl+C or kill the PID), then rerun the captured command directly with Tracy profiling arguments appended:

<captured kit command> \
  --/app/profilerBackend=tracy \
  --/app/profileFromStart=true \
  --/plugins/carb.profiler-tracy.plugin/fibersAsThreads=false \
  --/plugins/carb.profiler-tracy.plugin/instantEventsAsMessages=true \
  --/rtx/addTileGpuAnnotations=true \
  --/rtx/fullFrameNumberInTileGpuAnnotations_=true \
  --/profiler/channels/carb.events/enabled=false \
  --/profiler/channels/carb.tasking/enabled=false \
  --/profiler/channels/omni.usd.multitick.render.profile/enabled=true

This runs the kit executable directly (not through the test runner wrapper), so Tracy can connect to the process. The profiling settings must be command-line arguments — setting them in Python setUp() is too late since Tracy must initialize at process startup.

Step C — Capture with Tracy

Once the kit process is running with Tracy enabled, use tracy-capture to record the profile:

tracy-capture -o /tmp/unit_test_profile.tracy

Or connect the Tracy GUI profiler to the running process.

Key differences from standalone benchmarks

• Two-phase discovery: You must first run the test to discover the child command, then rerun it directly.
• Settings come from extension.toml: The --/ arguments are generated by the test infrastructure from the extension's test configuration — don't try to reconstruct them manually.
• No --gpu-frametime: Unit tests don't use the benchmark framework, so GPU frametime flags don't apply. Use Tracy's GPU zones instead.

Guidelines

• Never skip --gpu-frametime for standalone benchmarks — GPU-side timing is essential for rendering-heavy workloads.
• Keep arguments identical across runs for fair comparison. If the user changes arguments mid-iteration, note it clearly and treat it as a new baseline.
• Use --csv-self when you need to isolate a zone's own cost from its children.
• Read the .log file for the full benchmark stdout (summary report, warnings, errors) — it is always produced alongside the .tracy and .csv.
• Prompt for feedback after every iteration — don't silently chain multiple changes.