llm-instrumentation 1.3.1

A high-performance instrumentation framework for capturing, streaming, and analyzing internal activations of large language models

LLM Instrumentation Framework

A high-performance instrumentation framework for LLM interpretability and observability.

Objectives

• Throughput: Maintain ≥ 90% of un-instrumented inference speed.
• Data rate: Sustain ≥ 2 GB/s activation streaming to disk.
• Compression: Achieve ≥ 3× reduction with lossy error < 1e-3 when enabled.
• Memory: Keep host RAM usage ≤ 24 GB with backpressure and buffering.
• Resilience: Automatic checkpoints safeguard long generations from data loss.

Stack

• Runtime: PyTorch, asyncio, threading.
• GPU: Optional CUDA streams and pinned buffers (see memory/cuda_manager.py).
• Compression: LZ4, Zstd, optional no-op.
• Analysis: Hooks for downstream causal graphs and SAE-based features.

Install

python -m venv .venv && source .venv/bin/activate
pip install -r requirements.txt
pip install -e .

Quick Usage

import torch
from llm_instrumentation import capture_activations
from transformers import AutoModelForCausalLM

model = AutoModelForCausalLM.from_pretrained("meta-llama/Llama-2-7b-hf")

with capture_activations(model, preset="balanced", output_path="output.stream") as framework:
    _ = model(torch.randint(0, 100, (1, 16)))

analysis = framework.analyze_activations("output.stream")

## Per-token Tracking & Checkpointing (opt-in)

Enable lightweight token boundary tracking without affecting the compression/streaming pipeline. Token metadata is stored in memory and saved to `{output_path}_tokens.json` on context exit. Optional checkpoints persist snapshots every _N_ tokens to make long streaming sessions resumable.

```python
from llm_instrumentation import analyze_activations_with_tokens

with framework.capture_activations("gen.stream", track_per_token=True) as tracker:
    ids = torch.randint(0, 100, (1, 8))
    for _ in range(32):
        with torch.no_grad():
            out = model(ids)
            next_tok = out.logits[:, -1, :].argmax(dim=-1, keepdim=True)
        tracker.record_token(next_tok[0].item(), tokenizer.decode(next_tok[0]))
        ids = torch.cat([ids, next_tok], dim=-1)
        if next_tok[0].item() == tokenizer.eos_token_id:
            break

analysis = analyze_activations_with_tokens("gen.stream", framework)
print("bytes_per_token:", analysis.get("bytes_per_token"))

# Persist checkpoints every 64 tokens to allow resuming long captures.
with framework.capture_activations(
    "gen.stream",
    track_per_token=True,
    checkpoint_interval_tokens=64,
) as tracker:
    ...

# Resume the same capture later (appends to the existing stream file).
with framework.capture_activations(
    "gen.stream",
    track_per_token=True,
    checkpoint_interval_tokens=64,
    resume_from_checkpoint=True,
) as tracker:
    ...

Checkpoint files default to {output_path}.ckpt.json; override with checkpoint_path to control placement. Successful captures clean up checkpoints after flushing token metadata.

Configuration

• InstrumentationConfig.fast_capture() - minimal overhead capture without compression.
• InstrumentationConfig.max() - highest fidelity capture with maximum buffering.
• InstrumentationConfig.balanced() - default preset balancing throughput and compression.
• InstrumentationConfig.max_compression() - prioritize disk footprint with Zstd.
• InstrumentationConfig.attention_analysis() / .mlp_analysis() - capture subsets for focused studies.
• Builder-style overrides: e.g. InstrumentationConfig.balanced().with_compression("zstd").with_memory_limit(16).
• Direct parameters:
  • granularity (HookGranularity): FULL_TENSOR, SAMPLED_SLICES, ATTENTION_ONLY, MLP_ONLY.
  • compression_algorithm (str): "lz4", "zstd", or "none".
  • target_throughput_gbps (float): Desired streaming rate for tuning.
  • max_memory_gb (float|None): Budget for host buffering policies.

Refer to docs/API.md for full API details.

Automatic Configuration

The llm_instrumentation.core.auto_detect module can derive sensible defaults from a model instance:

from llm_instrumentation import capture_activations
from llm_instrumentation.core.auto_detect import create_optimized_config, detect_model_architecture

arch = detect_model_architecture(model)
config = create_optimized_config(arch, purpose="performance_analysis")
with capture_activations(model, config=config, output_path=f"{arch}.stream"):
    ...

This path keeps manual overrides available via the builder helpers while accelerating setup for common analysis workflows.

Stream Format

Each packet:

• Header: network-endian !HI → (name_len: uint16, data_len: uint32)
• Name: UTF-8 layer/module name (name_len bytes)
• Data: compressed tensor bytes (data_len bytes)

See docs/STREAM_FORMAT.md for a parsing example.

Architecture

E2E path: PyTorch forward hooks → async enqueue → compression workers → ring buffer → async file writer. See docs/ARCHITECTURE.md.

Benchmarks & Performance

Run scripts/run_benchmarks.sh and see docs/PERFORMANCE.md for targets, methodology, and how to generate reports.

Block I/O Instrumentation

Overview

STRAP-LLM includes eBPF-based block I/O monitoring to correlate disk performance with activation streaming:

• scripts/tracepoints.py: Captures latency histograms and queue depth using stable kernel tracepoints (block:block_rq_issue/block:block_rq_complete)
• scripts/analyze_tracepoints.py: Generates summaries and PNG visualizations from persisted JSONL snapshots

Quick Start

Collect I/O metrics:

sudo python3 scripts/tracepoints.py --interval 5 --output tracepoints.jsonl

Analyze results:

python3 scripts/analyze_tracepoints.py \
  --input tracepoints.jsonl \
  --output-dir ../benchmarks/systems/I-O

Features

• Low overhead: < 1% CPU usage, ~100ns per I/O request
• Stable ABI: Uses kernel tracepoints (no kprobes)
• Async persistence: Memory-mapped JSONL writer with batch flushes
• Log₂ histograms: Constant memory usage at any IOPS level
• Queue depth tracking: In-flight request monitoring per device

CLI Options

Flag	Description	Default
--interval	Sampling interval (seconds)	5.0
--output	JSONL output file	tracepoints.jsonl
--no-output	Disable file output	False
--flush-every	Snapshots per flush	12
--fsync	Force fsync after flush	False

Output Format

Each JSONL line contains:

• Timestamp (Unix epoch + ISO 8601)
• Per-device latency histogram (log₂ buckets in μs)
• Per-device in-flight request count

Example:

{
  "timestamp": 1696262400.123,
  "iso_timestamp": "2025-10-02T14:20:00.123000+00:00",
  "interval_s": 5.0,
  "latency_histogram": [
    {
      "device_name": "nvme0n1",
      "total": 45123,
      "buckets": [
        {"slot": 4, "count": 12000, "bucket_low": 16, "bucket_high": 31}
      ]
    }
  ],
  "inflight": [
    {"device_name": "nvme0n1", "count": 24}
  ]
}

Documentation

See docs/BLOCK_IO_TRACEPOINTS.md for:

• Prerequisites and installation
• Detailed usage examples
• Integration with LLM workflows
• Troubleshooting guide
• Performance characteristics
• Advanced customization

CPU & Memory Metrics

Overview

• scripts/system_metrics.py: Engancha tracepoints exceptions:page_fault_user y sched:sched_switch para capturar fallos de página por PID, tiempo fuera de CPU y presión PSI de CPU/I/O/memoria.
• Se ejecuta como root y persiste snapshots JSONL con los campos off_cpu_ns, page_faults y pressure cada N segundos.
• La salida complementa los histogramas de latencia/colas producidos por tracepoints.py para correlacionar latencia de servicio con contención de CPU, swapping y presión sistémica.

Quick Start

sudo python3 scripts/system_metrics.py --interval 5 --output system_metrics.jsonl

Cada línea JSON incluye timestamp, iso_timestamp, interval_s, un mapa off_cpu_ns (PID → nanosegundos fuera de CPU), page_faults (PID → fallos de página de usuario) y la estructura pressure con métricas PSI para CPU, I/O y memoria.

Para ver las muestras sólo por pantalla añade --no-output. Usa --flush-every y --fsync para controlar el flushing asíncrono en disco.

CLI Options

Flag	Description	Default
--interval	Intervalo entre snapshots (s)	5.0
--output	Archivo JSONL de salida	system_metrics.jsonl
--no-output	Deshabilita escritura a disco	False
--flush-every	Snapshots por flush	12
--fsync	Forzar fsync tras cada flush	False

Correlación

Combina system_metrics.jsonl y tracepoints.jsonl con scripts/analyze_tracepoints.py o cargas personalizadas en pandas para atribuir latencia a contención de CPU, fallos de página, presión PSI o I/O de disco.

Development

• Tests: pytest -q in repo root or the package directory.
• Examples: examples/basic_usage.py.
• Contributions: PRs welcome. Keep changes focused and covered by tests.