lucifer1004/veloq/pytorch-profile-analysis

PyTorch Profile Analysis

Use veloq pytorch for PyTorch/Kineto Chrome traces:

veloq pytorch summary T
veloq pytorch search T --type kernel --name-regex 'nccl|gemm' --limit 20
veloq pytorch inspect T kernel:91
veloq pytorch correlate T kernel:91
veloq pytorch slices T --aggregate --group-by step
veloq pytorch collectives T

This skill requires the VeloQ CLI on PATH. If veloq is missing, install it before analysis.

Tool Boundary

Use veloq pytorch verbs as the analysis interface. Do not query <input>.veloq/pytorch/ sidecars, generated Parquet files, or raw Kineto trace tables directly with DuckDB, PyArrow, pandas, or ad hoc SQL unless the user explicitly asks for raw-trace exploration or you are developing VeloQ itself.

veloq pytorch prep T only builds/checks sidecars. After prep, continue with summary, search, inspect, stats, correlate, timeline, slices, or collectives.

Inputs

• Explicit veloq pytorch commands accept one Chrome trace named .json

or .json.gz.

• Automatic source detection only claims .pt.trace.json and

.pt.trace.json.gz; explicitly select pytorch for other JSON filenames.

• Directory inputs are not supported in PyTorch v0. Ask the user to

choose one trace file if they point at a directory.

Row IDs

PyTorch row ids use <kind>:<stable_index>, where the stable index is derived from the original traceEvents order after non-event flow markers are skipped. Do not use Kineto Ev Idx as a stable key. Use veloq pytorch schema <target> for the authoritative response field inventory; do not infer the public contract from raw Kineto fields.

Common prefixes:

Workflow

1. Inventory first:

``bash veloq pytorch summary T ``

Read data.auxiliary.capabilities before choosing a path.

1. Find events:

``bash veloq pytorch search T --type cpu-op --name '*aten::*' --limit 20 veloq pytorch search T --type kernel --is-comm --limit 20 ``

1. Drill into one event:

``bash veloq pytorch inspect T ROW_ID ``

Inspect returns raw args, typed args, parent/children, enclosing step, and link metadata.

1. Answer launch-cause questions:

``bash veloq pytorch correlate T kernel:91 ``

Read data.rows[0].events[] for the CPU op, annotation/step, runtime/driver, and GPU activity chain.

1. Attribute CPU overhead to Python context when captured:

Traces exported from torch.profiler.profile(..., with_stack=True) include python_function events. inspect returns python_context / python_stack, and stats can group CPU work by python-context or python-path:

``bash veloq pytorch stats T --type cpu-op --group-by python-path,name --limit 20 veloq pytorch inspect T cpu_op:42 ``

1. Slice ProfilerStep/user annotation ranges:

slices --from/--to selects ranges that overlap the time window and clips attributed GPU/comm time to that window. Slice row start_ns and duration_ns remain the original trace range so the row id still points to the inspectable event.

1. For communication questions, stay within one trace file:

``bash veloq pytorch stats T --type comm --group-by comm-kind,rank veloq pytorch search T --type kernel --is-comm --limit 20 ``

collectives groups single-trace communication evidence and reports linked CPU/NCCL row ids. If a trace file contains multiple rank values, rank-scoped commands (search, stats, timeline, slices, and collectives) require --rank <n> or --all-ranks. inspect and correlate operate on explicit row ids and are not rank-scope gated. Device ids are rank-local and stream ids are device-local: filter a stream with --rank <n> --device <id> --stream <id>, or compare lanes with --group-by rank,device,stream. VeloQ does not compute cross-rank skew in PyTorch v0:

``bash veloq pytorch collectives T ``

Event Types

--type accepts cpu-op, annotation, step, runtime, driver, kernel, memcpy, memset, memory, python, comm, or all.

comm is a communication-related set. Use --type kernel --is-comm to focus on NCCL kernels.

Limits

PyTorch support is experimental (source.version = "v0"). Classification is based on Kineto category/name/arg conventions and may need extension for profiler variants not yet represented by tests. Treat documented fields, schema targets, row ids/keys, command ids, and output modes as the versioned source contract even while the source remains v0.