performance-analysis

name	performance-analysis
description	Analyze MaxText training job performance using tgs_tagger, TraceLens, and IRLens. Use when the user asks to analyze a training run, profile traces, HLO IR, TGS metrics, GPU utilization, or mentions tag_tgs, TraceLens, IRLens, xplane, or performance analysis.

MaxText Performance Analysis

Post-training (or mid-training) analysis pipeline. Follow the workflow below from top to bottom.

Multi-job comparisons: If comparing two or more jobs (e.g., "why is job B slower than job A?"), start with skills/tsdb-diagnosis/SKILL.md (Multi-Job Comparison workflow) before running TraceLens. The TSDB reveals system-level root causes — CPU contention from RCCL resource leaks, network errors, I/O pressure, thermal throttling — that TraceLens cannot observe (it only sees GPU-side kernel timings). Only proceed to TraceLens here if the TSDB comparison is inconclusive.

Deep per-kernel analysis: When the user asks for per-kernel time breakdowns, step-time composition tables, cross-variant kernel comparisons, or whether a specific kernel is main-stream-blocking — switch to skills/profile-drill/SKILL.md. TraceLens's kernel_launchers_summary_by_category.csv has a known ~1.5×–2× inflation bug on 1-node/proc profiles (the time ms per gpu column divides by host count, not GPU count). profile-drill uses utils/profile_drill.py to read the raw xplane trace JSONs directly and avoids this bias.

Workflow

Step 1: Run the dispatcher

python3 utils/analyze_job.py "$JOB_WORKSPACE/<job>.log"
python3 utils/analyze_job.py "$JOB_WORKSPACE/<job_dir>/"
python3 utils/analyze_job.py "$JOB_WORKSPACE/local_2026*"

For running jobs, pass -f to force re-analysis (bypasses staleness check):

python3 utils/analyze_job.py -f "$JOB_WORKSPACE/<job>.log"

The dispatcher auto-detects available artifacts and runs only the relevant tools:

• Log with TGS data → tgs_tagger.py
• *.xplane.pb → TraceLens_generate_perf_report_jax
• xla_dump/*.gpu_after_optimizations.txt → IRLens_analyze_hlo_ir.py

Step 2: Handle TraceLens if needed

If the dispatcher output says "TraceLens not installed" and xplane traces exist:

1. Check if TraceLens is already installed and patched before doing anything:

   python3 -c "
   import TraceLens.util, inspect
   src = inspect.getsource(TraceLens.util.DataLoader.load_data)
   assert 'xprof' in src, 'not patched'
   print('TraceLens: installed and patched')
   "
   

   • Succeeds → TraceLens is ready. Just re-run: python3 utils/analyze_job.py -f "$JOB_WORKSPACE/<job>.log"
   • ImportError → not installed. Install then patch (see below).
   • AssertionError → installed but unpatched. Patch only (see below).

2. Install (only if import failed):

   pip install git+https://github.com/AMD-AGI/TraceLens.git
   

3. Patch (only if the xprof assertion failed). Apply all patches from tracelens-patches.md — 6 files, ~13 patches. Key fixes:

   • protobuf/xprof import errors (TF 2.19+ renamed tensorboard_plugin_profile to xprof)
   • GPU PID remapping (xprof remaps device PIDs to 1001+; code filtering pid < 100 misses all GPU events)
   • metadata_events not passed to build_tree()
   • KeyError on gpu_kernel_op_cat and missing parent events for launch latency

4. Re-run the dispatcher with -f:

   python3 utils/analyze_job.py -f "$JOB_WORKSPACE/<job>.log"
   

This is one-time per environment. Always check before patching to avoid redundant work.

Step 3: Read results

Read the generated analysis.json — but do NOT try to read the raw file (it can be 40K+ lines due to per-step arrays). Extract key metrics programmatically:

python3 -c "
import json, sys
with open('<job_dir>/analysis.json') as f:
    d = json.load(f)
print(f'Job: {d[\"job_id\"]} | Model: {d[\"model\"]} | Nodes: {d[\"num_nodes\"]} | Status: {d[\"job_status\"][\"status\"]}')
tgs = d['tgs']
print(f'Steady TGS: {tgs[\"steady\"][\"mean\"]:.1f} (std={tgs[\"steady\"][\"std\"]:.1f}, steps {tgs[\"steady\"][\"range\"]})')
print(f'Tail   TGS: {tgs[\"tail\"][\"mean\"]:.1f} (std={tgs[\"tail\"][\"std\"]:.1f}, steps {tgs[\"tail\"][\"range\"]})')
tl = d.get('tracelens_summary', {})
if tl:
    print(f'Compute: {tl[\"computation_time\"]:.1f}% | Exposed comm: {tl[\"exposed_comm_time\"]:.1f}% | Idle: {tl[\"idle_time\"]:.2f}% | Total comm: {tl[\"total_comm_time\"]:.1f}%')
"

For deeper TraceLens analysis, read the CSVs in <job_dir>/tracelens/<timestamp>/csvs/:

• gpu_events_averages.csv — per-GPU compute/comm/idle breakdown (averages)
• gpu_timeline.csv — per-GPU breakdown with pid
• kernel_launchers_summary_by_category.csv — time by kernel category (GEMM, NCCL, XLA fusions, etc.)
• kernel_launchers_summary.csv — time by individual kernel name

⚠️ TraceLens per-GPU CSV bias on 1-node/proc. The time ms per gpu column in the two kernel_launchers_summary*.csv files divides total kernel time by host count (typically 8), not GPU count (typically 64) — so per-GPU numbers are ~1.5×–2× inflated on 1-node/proc profiles. Percentages and category rankings are fine; absolute per-GPU kernel times are not. For kernel-time numbers you can cite (e.g. in a report or step-time composition table), use skills/profile-drill/SKILL.md instead — it reads raw xplane trace JSONs and divides by auto-detected GPUs.

Step 4: Summarize findings

Present results using this structure:

Metric	Source	What to look for
TGS (steady-state)	analysis.json → tgs.steady	Primary throughput metric
MFU	analysis.json → mfu_per_step	Model FLOPS utilization (if available)
GPU compute %	tracelens_summary.computation_time	Time on actual compute kernels
Exposed comm %	tracelens_summary.exposed_comm_time	Communication NOT overlapped with compute (lower is better)
Idle %	tracelens_summary.idle_time	GPU doing nothing (should be near 0)
Kernel breakdown	kernel_launchers_summary_by_category.csv	GEMM vs NCCL vs fusion time
Comm ops per step	dispatcher IRLens output	Count of all-reduce, all-gather, all-to-all, reduce-scatter

Interpretation guidelines:

• High exposed comm % → opportunities for better comm/compute overlap
• Large per-GPU variance in compute % → load imbalance
• High idle % → scheduling or synchronization issues
• Tail TGS std much larger than steady std → periodic overhead (checkpointing, profiling)

Step 5: Ensure dashboard is running

Check the dispatcher output first — it prints a Dashboard: line at the end. If it shows a URL with (running), use that URL.

If the dashboard is not running, start it:

pip install fastapi uvicorn   # one-time
utils/perf_server.py &        # binds 127.0.0.1 by default

Always tell the user the dashboard URL: http://localhost:<PORT>. For remote access, instruct them to tunnel: ssh -L <PORT>:localhost:<PORT> user@host. Avoid --host 0.0.0.0 — perf_server.py has no auth.

The server auto-detects a free port starting from 8080 and auto-reloads analysis.json on each request.

Reference

Job output layout

<JOB_WORKSPACE>/<JOB_ID>-<JOB_NAME>[-TGS_<VALUE>]/
  log -> ../<log_file>                          # symlink to log file
  analysis.json                                 # structured metrics
  xla_dump/                                     # if _env_ENABLE_XLA_DUMP=1
    module_NNNN.jit_train_step.*_gpu_after_optimizations.txt
  <run_name>/tensorboard/plugins/profile/<ts>/  # if profiler=xplane
    <hostname>.xplane.pb                        #   1-node/proc: one per host
  <run_name>/tensorboard/plugins/profile/<ts_i>/ # 1-GPU/proc (LOCAL_WORLD_SIZE ts dirs,
    <hostname>.proc<N>.xplane.pb                #   one file per host per ts;
                                                #   successive serialized writes land
                                                #   in different per-second ts dirs)
  tracelens/<ts>/csvs/*.csv                     # 1-node/proc: TraceLens output
  tracelens/<ts_i>/<hostname>.proc<N>/csvs/*.csv # 1-GPU/proc: one dir per GPU

The .log file sits alongside the directory in <JOB_WORKSPACE>/.

When enable_checkpointing=true, profiler traces may end up in a shared directory outside the job dir. analyze_job.py parses Config param tensorboard_dir from the log to locate these. The dispatcher and perf_server.py filter profiles by job execution time window and node-0 hostname to disambiguate. In 1-GPU-per-process mode the node-0 filter name.startswith("<host>.") still matches all <host>.proc<N>.xplane.pb files, so TraceLens runs once per GPU on node 0; the multiple timestamp dirs (one per serialized write) are treated like periodic-profiling windows by the existing code.

Running individual tools directly

These are rarely needed — analyze_job.py orchestrates them. Use only for targeted re-runs.

# TGS tagging
utils/tag_tgs.sh <log_file_or_glob>
utils/tag_tgs.sh -f <log_file>       # force on running job

# IRLens
utils/IRLens_analyze_hlo_ir.py <hlo_file>
utils/IRLens_analyze_hlo_ir.py <hlo_file> --op communication
utils/IRLens_analyze_hlo_ir.py <hlo_file> --op computation

# TraceLens
TraceLens_generate_perf_report_jax \
    --profile_path <xplane.pb> \
    --output_csvs_dir <output_dir>/csvs

# profile_drill.py — direct per-kernel analysis from trace JSONs
# (use when TraceLens's per-GPU numbers are suspect or you need kernel-level
# ground truth; see skills/profile-drill/SKILL.md)
utils/profile_drill.py <job_dir>/.../tensorboard/plugins/profile/*/*.trace.json.gz

RAY=1 Slurm log truncation

For RAY=1 jobs, the Slurm log may contain fewer training steps than actually completed due to Ray output buffering (actor stdout is forwarded asynchronously to the driver, and unflushed output is lost when the job exits). If the analysis shows suspiciously few steps (e.g., 34 out of 100) with no error or JOB SUMMARY, check ray_logs/<head_node>/worker*.out in the job directory for the authoritative step count. The analysis.json TGS/MFU metrics will be based only on what appears in the Slurm log and may undercount the actual run.

Running jobs

• The dispatcher detects running jobs via the JOB SUMMARY log marker and file modification time (15 min threshold).
• analyze_job.py -f bypasses the staleness check but never renames files for running jobs. Renames happen automatically on the next analysis after the job finishes.
• TraceLens needs a completed profiler trace; skipped if *.xplane.pb doesn't exist yet.
• IRLens works on running jobs if xla_dump/ is already populated.