profiling

Profiling Guide

This is the agent-facing profiling workflow for Kit-based applications (Isaac Sim, Isaac Lab, Kit SDK). dev/docs/profiling-guide.md is the source of truth; keep this skill aligned with that guide.

Benchmark Accuracy: COLD / WARM / TRACY

Profilers add overhead. Keep measurement and diagnosis as separate runs:

1. COLD: first run after a fresh install/cache state. Use this to expose startup and shader-cache effects, not as the steady-state performance number.
2. WARM: same workload with caches already populated and profiling disabled. This is the authoritative FPS/frametime benchmark run.
3. TRACY: same cache state as WARM, Tracy backend enabled, CARB_PROFILING_PYTHON=1 set, and .tracy captured via a separate capture process. Use this for analysis only, not headline numbers.

Never report benchmark performance from a profiled run. Nsight Systems captures are also analysis-only and have their own overhead.

CPU ChromeTrace Backend

Use the CPU backend for short, shareable, offline captures or targeted runtime intervals.

Kit Args

--/app/profilerBackend=cpu
--/app/profileFromStart=true
--/profiler/enabled=true
--/plugins/carb.profiler-cpu.plugin/saveProfile=1
--/plugins/carb.profiler-cpu.plugin/compressProfile=1
--/plugins/carb.profiler-cpu.plugin/filePath=mytrace.gz

Runtime On/Off

import carb.profiler

profiler = carb.profiler.acquire_profiler_interface()
profiler.set_capture_mask(1)  # start targeted capture
# ... section to profile ...
profiler.set_capture_mask(0)  # stop targeted capture

Convert Chrome Trace JSON to Tracy

# From the Tracy binary directory
./import-chrome input_trace.json output.tracy

Tracy Profiling

Environment Setup

export TRACY_NO_SYS_TRACE=1
export TRACY_NO_CALLSTACK=1
export TRACY_PORT="${TRACY_PORT:-8086}"  # Isaac Sim 6.0+ commonly uses 8087 to avoid OV Hub

# TRACY analysis phase only. Do not set during COLD/WARM benchmark measurement.
export CARB_PROFILING_PYTHON=1

Kit Args (common for all Kit-based products)

--/app/profilerBackend=tracy
--/app/profileFromStart=true
--/profiler/enabled=true
--/profiler/gpu=true
--/profiler/gpu/tracyInject/enabled=true
--/app/profilerMask=1
--/plugins/carb.profiler-tracy.plugin/fibersAsThreads=false
--/profiler/channels/carb.events/enabled=false
--/profiler/channels/carb.tasking/enabled=false
--/profiler/gpu/tracyInject/msBetweenClockCalibration=0
--/rtx/addTileGpuAnnotations=true
--/plugins/carb.profiler-tracy.plugin/instantEventsAsMessages=true

Tracy Capture — Correct Procedure (IMPORTANT)

Tracy capture is error-prone. Follow this exact sequence to avoid port conflicts and data loss.

Tracy port: default is 8086; Isaac Sim 6.0+ commonly uses 8087 to avoid OV Hub. Kit auto-increments to 8087, 8088, etc. on conflict. Set TRACY_PORT when you know the port.

Tracy capture binary: use the bundled omni.kit.profiler.tracy capture binary when available, or build the Tracy version that matches Kit's carb_sdk_plugins from source.

Check Kit's all-deps.packman.xml before building a fallback capture binary. For current Kit builds, use Tracy v0.11.1 and the headless binary at capture/build/unix/capture-release.

Step-by-step:

# 1. Kill any existing Tracy-related processes hogging the port
pkill -9 -f "capture" 2>/dev/null || true
export TRACY_PORT="${TRACY_PORT:-8086}"  # use 8087 for Isaac Sim 6.0+ when needed
ss -tlnp | grep ":$TRACY_PORT" || true  # verify the intended port is free

BENCH_SCRIPT="standalone_examples/benchmarks/benchmark_camera.py"
RESULT_DIR="/tmp/isaacsim-profile-results"

TRACY_CAPTURE_BIN="${TRACY_CAPTURE_BIN:-}"
if [ -z "$TRACY_CAPTURE_BIN" ]; then
  TRACY_CAPTURE_BIN=$(command -v capture || command -v capture-release || command -v tracy-capture)
fi
[ -n "$TRACY_CAPTURE_BIN" ] || { echo "Missing Tracy capture binary"; exit 1; }

# 2. Start the application FIRST (in background)
nohup ./python.sh "$BENCH_SCRIPT" \
  --num-cameras 1 --num-frames 600 \
  --/app/profilerBackend=tracy --/app/profileFromStart=true \
  --/profiler/enabled=true --/profiler/gpu=true \
  --/profiler/gpu/tracyInject/enabled=true --/app/profilerMask=1 \
  --/plugins/carb.profiler-tracy.plugin/fibersAsThreads=false \
  --/profiler/channels/carb.events/enabled=false \
  --/profiler/channels/carb.tasking/enabled=false \
  --/profiler/gpu/tracyInject/msBetweenClockCalibration=0 \
  --/rtx/addTileGpuAnnotations=true \
  --/plugins/carb.profiler-tracy.plugin/instantEventsAsMessages=true \
  --/exts/isaacsim.benchmark.services/metrics/metrics_output_folder="$RESULT_DIR" \
  > /tmp/app.log 2>&1 &
APP_PID=$!

# 3. Poll until Tracy port is open (app needs time to initialize)
for i in $(seq 1 60); do
  ss -tlnp | grep -q ":$TRACY_PORT" && break
  sleep 2
done

# 4. Start capture AFTER port is confirmed open
"$TRACY_CAPTURE_BIN" -o trace_output.tracy -f -p "$TRACY_PORT" &
CAPTURE_PID=$!

# 5. Wait for benchmark result files, not graceful Isaac Sim shutdown
until ls "$RESULT_DIR"/kpis_*.json >/dev/null 2>&1; do sleep 5; done

# 6. Isaac Sim can hang during Tracy shutdown. Force-kill after outputs exist.
kill -9 "$APP_PID" "$CAPTURE_PID" 2>/dev/null || true

Critical warnings:

• Prefer app first, then capture. Starting capture before the app can work, but app-first plus port verification is the most reliable sequence.
• NEVER kill capture with kill/SIGTERM. It will NOT save the trace file.
• Always check for zombie processes on the intended Tracy port before starting.
• Do not wait for Isaac Sim graceful shutdown after benchmark outputs exist; Tracy shutdown can hang. Use kill -9 as the guide-prescribed last resort.

Last Resort: Scoped os._exit(0) Close Patch

Do not patch installed Isaac Sim files by default. Normal shutdown is preferred because it runs cleanup code and keeps the install reproducible.

Use this workaround only when all of the following are true:

• The workload repeatedly hangs during Tracy shutdown.
• Expected benchmark and trace outputs already exist with non-zero size.
• The install is disposable or you can restore the original file immediately after capture.

Prefer first to use the force-kill sequence above after results are complete. Patch only when repeated hangs prevent usable capture completion.

# Find simulation_app.py — path varies between source and build layouts:
#   Source build: source/extensions/isaacsim.simulation_app/isaacsim/simulation_app/simulation_app.py
#   Build output: _build/linux-x86_64/release/exts/isaacsim.simulation_app/isaacsim/simulation_app/simulation_app.py
# NOTE: `find -path` may fail in some environments (dots in dir names). Use glob instead:
shopt -s globstar nullglob
PACKAGE_PATH="/path/to/IsaacSim-or-pip-package"
SIM_APP=$(echo "$PACKAGE_PATH"/**/isaacsim/simulation_app/simulation_app.py | tr ' ' '\n' | grep -v __pycache__ | head -1)
# Or explicit known paths:
# SIM_APP="$PACKAGE_PATH"/_build/linux-x86_64/release/exts/isaacsim.simulation_app/isaacsim/simulation_app/simulation_app.py
echo "Found: $SIM_APP"

# Idempotent patch with a restore point.
cp -n "$SIM_APP" "$SIM_APP.bak.codex-tracy-close"
python3 - "$SIM_APP" <<'PY'
from pathlib import Path
import re, sys

path = Path(sys.argv[1])
text = path.read_text()
marker = "CODEX_TRACY_CLOSE_BYPASS"
if marker in text:
    print(f"Already patched: {path}")
    raise SystemExit(0)

patched, count = re.subn(
    r"(^\s*def close\(self[^)]*\):\n)",
    r"\1        # CODEX_TRACY_CLOSE_BYPASS: last-resort workaround for Tracy shutdown hangs.\n        import os; os._exit(0)\n",
    text,
    count=1,
    flags=re.MULTILINE,
)
if count != 1:
    raise SystemExit(f"Could not find close() in {path}")
path.write_text(patched)
print(f"Patched: {path}")
PY

# Verify the patch applied
grep -n 'CODEX_TRACY_CLOSE_BYPASS' "$SIM_APP"

# Restore after the capture
cp "$SIM_APP.bak.codex-tracy-close" "$SIM_APP"

Last Resort: Force-kill Hung Benchmarks When Results Exist

If ALL expected output files exist with non-zero size, and the process is still running after 2+ minutes with no new output, it is probably hung. Follow the guide sequence and force-kill the app and capture processes:

RESULT_DIR="/tmp/isaacsim-profile-results"
APP_PID=12345
CAPTURE_PID=12346

ls -la "$RESULT_DIR"/kpis_*.json "$RESULT_DIR"/*.tracy 2>/dev/null
# If files exist and size > 0:
kill -9 "$APP_PID" "$CAPTURE_PID" 2>/dev/null || true

Nsight Systems Profiling

Install

# Linux: download from https://developer.nvidia.com/nsight-systems
sudo dpkg -i nsight-systems-*.deb

# Windows: download the latest standalone .msi from https://developer.nvidia.com/nsight-systems

Kit Args for NVTX

--/app/profileFromStart=true
--/profiler/enabled=true
--/app/profilerBackend=nvtx
--/profiler/gpu=true
--/app/profilerMask=1
--/plugins/carb.profiler-tracy.plugin/fibersAsThreads=false
--/profiler/channels/carb.events/enabled=false
--/profiler/channels/carb.tasking/enabled=false

Nsys Command

export CARB_PROFILING_PYTHON=1
NSYS_OUTPUT="kit_profile"

sudo nsys profile \
  --force-overwrite=true \
  --output="$NSYS_OUTPUT" \
  --sample=system-wide \
  --trace=cuda,nvtx,vulkan,osrt \
  --gpu-metrics-devices=all \
  --gpuctxsw=true \
  --cuda-memory-usage=true \
  --cuda-graph-trace=graph:host-and-device \
  ./python.sh standalone_examples/benchmarks/benchmark_camera.py \
  --num-cameras 1 --num-frames 100 --headless \
  --/app/profileFromStart=true --/profiler/enabled=true \
  --/app/profilerBackend=nvtx --/app/profilerMask=1 \
  --/plugins/carb.profiler-tracy.plugin/fibersAsThreads=false \
  --/profiler/channels/carb.events/enabled=false \
  --/profiler/channels/carb.tasking/enabled=false

Windows nsys Differences

• -t osrt is NOT supported on Windows (use -t wddm)
• nsys profile CANNOT profile .bat files — must target .exe directly
• nsys stats may fail with UnicodeDecodeError — export to SQLite instead
• Must cd to the directory containing the target exe

Analyzing Profiles

For NVTX zone interpretation and phase detection config, see the nsys-analyze skill.

Product-Specific Profiling Examples

Isaac Sim with Tracy:

./python.sh standalone_examples/benchmarks/benchmark_camera.py \
  --num-cameras 1 --resolution 1920 1080 --num-gpus 1 --num-frames 600 \
  --/app/profilerBackend=tracy --/app/profileFromStart=true \
  --/profiler/enabled=true --/profiler/gpu=true \
  --/profiler/gpu/tracyInject/enabled=true --/app/profilerMask=1 \
  --/plugins/carb.profiler-tracy.plugin/fibersAsThreads=false \
  --/profiler/channels/carb.events/enabled=false \
  --/profiler/channels/carb.tasking/enabled=false \
  --/profiler/gpu/tracyInject/msBetweenClockCalibration=0 \
  --/rtx/addTileGpuAnnotations=true \
  --/plugins/carb.profiler-tracy.plugin/instantEventsAsMessages=true \
  --/exts/isaacsim.benchmark.services/metrics/metrics_output_folder=/tmp/results

Isaac Sim with Nsight:

export CARB_PROFILING_PYTHON=1

sudo prlimit --nofile=65536:65536 /bin/bash -c \
"export OMNI_KIT_ALLOW_ROOT=1; \
 export DISPLAY=:0; \
 export OMNI_PASS='<YOUR_API_KEY>'; \
 export OMNI_USER='\$omni-api-token'; \
 nsys profile \
   --force-overwrite=true \
   --output=isaacsim_profile \
   --sample=system-wide \
   --trace=cuda,nvtx,vulkan,osrt \
   --gpu-metrics-devices=all \
   --gpuctxsw=true \
   --cuda-memory-usage=true \
   --cuda-graph-trace=graph:host-and-device \
   ./python.sh standalone_examples/benchmarks/benchmark_camera.py \
   --num-cameras 1 --num-frames 100 --headless \
   --/app/profileFromStart=true --/profiler/enabled=true \
   --/app/profilerBackend=nvtx --/app/profilerMask=1 \
   --/plugins/carb.profiler-tracy.plugin/fibersAsThreads=false \
   --/profiler/channels/carb.events/enabled=false \
   --/profiler/channels/carb.tasking/enabled=false"

Isaac Lab with Nsight:

sudo OMNI_KIT_ALLOW_ROOT=1 DISPLAY=:0 \
  TRACY_NO_SYS_TRACE=1 TRACY_NO_CALLSTACK=1 CARB_PROFILING_PYTHON=1 \
  nsys profile --force-overwrite=true --output=isaaclab_profile \
  --sample=system-wide --trace=cuda,nvtx,vulkan,osrt \
  --gpu-metrics-devices=all --gpuctxsw=true \
  --cuda-memory-usage=true --cuda-graph-trace=graph:host-and-device \
  ./isaaclab.sh -p scripts/benchmarks/benchmark_non_rl.py \
  --task=Isaac-Cartpole-Direct-v0 --viz none --num_frames 100 \
  --kit_args "--/app/profileFromStart=true --/profiler/enabled=true --/app/profilerBackend=nvtx --/app/profilerMask=1 --/plugins/carb.profiler-tracy.plugin/fibersAsThreads=false --/profiler/channels/carb.events/enabled=false --/profiler/channels/carb.tasking/enabled=false"

Export Handoff

Export traces here, then use nsys-analyze for SQL queries, Tracy Statistics/Range Limit comparison, zone ranking, phase detection, and interpretation. Tracy capture already applies LZ4 compression. For sharing very large .tracy files, optionally recompress with update -z 1.

nsys export --type=sqlite -o profile.sqlite profile.nsys-rep
csvexport profile.tracy > zones.csv

TRACY_UPDATE_BIN=$(command -v update || command -v tracy-update || true)
[ -n "$TRACY_UPDATE_BIN" ] && "$TRACY_UPDATE_BIN" -z 1 profile.tracy profile.recompressed.tracy

CPU Governor — Performance Mode

MANDATORY before any benchmark. See the perf-tuning skill for commands and details.