Distributed Llm Pretraining Torchtitan

Distributed Llm Pretraining Torchtitan

Provides PyTorch-native distributed LLM pretraining using torchtitan with 4D parallelism (FSDP2, TP, PP, CP). Use when pretraining Llama 3.1, DeepSeek V3, or custom models at scale from 8 to 512+ GPUs with Float8, torch.compile, and distributed checkpointing.

Skill metadata

Source	Optional — install with hermes skills install official/mlops/torchtitan
Path	optional-skills/mlops/torchtitan
Version	1.0.0
Author	Orchestra Research
License	MIT
Dependencies	torch>=2.6.0, torchtitan>=0.2.0, torchao>=0.5.0
Tags	Model Architecture, Distributed Training, TorchTitan, FSDP2, Tensor Parallel, Pipeline Parallel, Context Parallel, Float8, Llama, Pretraining

Reference: full SKILL.md

The following is the complete skill definition that Hermes loads when this skill is triggered. This is what the agent sees as instructions when the skill is active.

TorchTitan - PyTorch Native Distributed LLM Pretraining

Quick start

TorchTitan is PyTorch’s official platform for large-scale LLM pretraining with composable 4D parallelism (FSDP2, TP, PP, CP), achieving 65%+ speedups over baselines on H100 GPUs.

Installation:

# From PyPI (stable)
pip install torchtitan

# From source (latest features, requires PyTorch nightly)
git clone https://github.com/pytorch/torchtitan
cd torchtitan
pip install -r requirements.txt

Download tokenizer:

# Get HF token from https://huggingface.co/settings/tokens
python scripts/download_hf_assets.py --repo_id meta-llama/Llama-3.1-8B --assets tokenizer --hf_token=...

Start training on 8 GPUs:

CONFIG_FILE="./torchtitan/models/llama3/train_configs/llama3_8b.toml" ./run_train.sh

Common workflows

Workflow 1: Pretrain Llama 3.1 8B on single node

Copy this checklist:

Single Node Pretraining:
- [ ] Step 1: Download tokenizer
- [ ] Step 2: Configure training
- [ ] Step 3: Launch training
- [ ] Step 4: Monitor and checkpoint

Step 1: Download tokenizer

python scripts/download_hf_assets.py \
  --repo_id meta-llama/Llama-3.1-8B \
  --assets tokenizer \
  --hf_token=YOUR_HF_TOKEN

Step 2: Configure training

Edit or create a TOML config file:

llama3_8b_custom.toml

[job]
dump_folder = "./outputs"
description = "Llama 3.1 8B training"

[model]
name = "llama3"
flavor = "8B"
hf_assets_path = "./assets/hf/Llama-3.1-8B"

[optimizer]
name = "AdamW"
lr = 3e-4

[lr_scheduler]
warmup_steps = 200

[training]
local_batch_size = 2
seq_len = 8192
max_norm = 1.0
steps = 1000
dataset = "c4"

[parallelism]
data_parallel_shard_degree = -1  # Use all GPUs for FSDP

[activation_checkpoint]
mode = "selective"
selective_ac_option = "op"

[checkpoint]
enable = true
folder = "checkpoint"
interval = 500

Step 3: Launch training

# 8 GPUs on single node
CONFIG_FILE="./llama3_8b_custom.toml" ./run_train.sh

# Or explicitly with torchrun
torchrun --nproc_per_node=8 \
  -m torchtitan.train \
  --job.config_file ./llama3_8b_custom.toml

Step 4: Monitor and checkpoint

TensorBoard logs are saved to ./outputs/tb/:

tensorboard --logdir ./outputs/tb

Workflow 2: Multi-node training with SLURM

Multi-Node Training:
- [ ] Step 1: Configure parallelism for scale
- [ ] Step 2: Set up SLURM script
- [ ] Step 3: Submit job
- [ ] Step 4: Resume from checkpoint

Step 1: Configure parallelism for scale

For 70B model on 256 GPUs (32 nodes):

[parallelism]
data_parallel_shard_degree = 32  # FSDP across 32 ranks
tensor_parallel_degree = 8        # TP within node
pipeline_parallel_degree = 1      # No PP for 70B
context_parallel_degree = 1       # Increase for long sequences

Step 2: Set up SLURM script

#!/bin/bash
#SBATCH --job-name=llama70b
#SBATCH --nodes=32
#SBATCH --ntasks-per-node=8
#SBATCH --gpus-per-node=8

srun torchrun \
  --nnodes=32 \
  --nproc_per_node=8 \
  --rdzv_backend=c10d \
  --rdzv_endpoint=$MASTER_ADDR:$MASTER_PORT \
  -m torchtitan.train \
  --job.config_file ./llama3_70b.toml

Step 3: Submit job

sbatch multinode_trainer.slurm

Step 4: Resume from checkpoint

Training auto-resumes if checkpoint exists in configured folder.

Workflow 3: Enable Float8 training for H100s

Float8 provides 30-50% speedup on H100 GPUs.

Float8 Training:
- [ ] Step 1: Install torchao
- [ ] Step 2: Configure Float8
- [ ] Step 3: Launch with compile

Step 1: Install torchao

USE_CPP=0 pip install git+https://github.com/pytorch/ao.git

Step 2: Configure Float8

Add to your TOML config:

[model]
converters = ["quantize.linear.float8"]

[quantize.linear.float8]
enable_fsdp_float8_all_gather = true
precompute_float8_dynamic_scale_for_fsdp = true
filter_fqns = ["output"]  # Exclude output layer

[compile]
enable = true
components = ["model", "loss"]

Step 3: Launch with compile

CONFIG_FILE="./llama3_8b.toml" ./run_train.sh \
  --model.converters="quantize.linear.float8" \
  --quantize.linear.float8.enable_fsdp_float8_all_gather \
  --compile.enable

Workflow 4: 4D parallelism for 405B models

4D Parallelism (FSDP + TP + PP + CP):
- [ ] Step 1: Create seed checkpoint
- [ ] Step 2: Configure 4D parallelism
- [ ] Step 3: Launch on 512 GPUs

Step 1: Create seed checkpoint

Required for consistent initialization across PP stages:

NGPU=1 CONFIG_FILE=./llama3_405b.toml ./run_train.sh \
  --checkpoint.enable \
  --checkpoint.create_seed_checkpoint \
  --parallelism.data_parallel_shard_degree 1 \
  --parallelism.tensor_parallel_degree 1 \
  --parallelism.pipeline_parallel_degree 1

Step 2: Configure 4D parallelism

[parallelism]
data_parallel_shard_degree = 8   # FSDP
tensor_parallel_degree = 8       # TP within node
pipeline_parallel_degree = 8     # PP across nodes
context_parallel_degree = 1      # CP for long sequences

[training]
local_batch_size = 32
seq_len = 8192

Step 3: Launch on 512 GPUs

# 64 nodes x 8 GPUs = 512 GPUs
srun torchrun --nnodes=64 --nproc_per_node=8 \
  -m torchtitan.train \
  --job.config_file ./llama3_405b.toml

When to use vs alternatives

Use TorchTitan when:

• Pretraining LLMs from scratch (8B to 405B+)
• Need PyTorch-native solution without third-party dependencies
• Require composable 4D parallelism (FSDP2, TP, PP, CP)
• Training on H100s with Float8 support
• Want interoperable checkpoints with torchtune/HuggingFace

Use alternatives instead:

• Megatron-LM: Maximum performance for NVIDIA-only deployments
• DeepSpeed: Broader ZeRO optimization ecosystem, inference support
• Axolotl/TRL: Fine-tuning rather than pretraining
• LitGPT: Educational, smaller-scale training

Common issues

Issue: Out of memory on large models

Enable activation checkpointing and reduce batch size:

[activation_checkpoint]
mode = "full"  # Instead of "selective"

[training]
local_batch_size = 1

Or use gradient accumulation:

[training]
local_batch_size = 1
global_batch_size = 32  # Accumulates gradients

Issue: TP causes high memory with async collectives

Set environment variable:

export TORCH_NCCL_AVOID_RECORD_STREAMS=1

Issue: Float8 training not faster

Float8 only benefits large GEMMs. Filter small layers:

[quantize.linear.float8]
filter_fqns = ["attention.wk", "attention.wv", "output", "auto_filter_small_kn"]

Issue: Checkpoint loading fails after parallelism change

Use DCP’s resharding capability:

# Convert sharded checkpoint to single file
python -m torch.distributed.checkpoint.format_utils \
  dcp_to_torch checkpoint/step-1000 checkpoint.pt

Issue: Pipeline parallelism initialization

Create seed checkpoint first (see Workflow 4, Step 1).

Supported models

Model	Sizes	Status
Llama 3.1	8B, 70B, 405B	Production
Llama 4	Various	Experimental
DeepSeek V3	16B, 236B, 671B (MoE)	Experimental
GPT-OSS	20B, 120B (MoE)	Experimental
Qwen 3	Various	Experimental
Flux	Diffusion	Experimental

Performance benchmarks (H100)

Model	GPUs	Parallelism	TPS/GPU	Techniques
Llama 8B	8	FSDP	5,762	Baseline
Llama 8B	8	FSDP+compile+FP8	8,532	+48%
Llama 70B	256	FSDP+TP+AsyncTP	876	2D parallel
Llama 405B	512	FSDP+TP+PP	128	3D parallel

Advanced topics

FSDP2 configuration: See references/fsdp.md for detailed FSDP2 vs FSDP1 comparison and ZeRO equivalents.

Float8 training: See references/float8.md for tensorwise vs rowwise scaling recipes.

Checkpointing: See references/checkpoint.md for HuggingFace conversion and async checkpointing.

Adding custom models: See references/custom-models.md for TrainSpec protocol.

Resources

• GitHub: https://github.com/pytorch/torchtitan
• Paper: https://arxiv.org/abs/2410.06511
• ICLR 2025: https://iclr.cc/virtual/2025/poster/29620
• PyTorch Forum: https://discuss.pytorch.org/c/distributed/torchtitan/44