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title: "Accelerate — Run PyTorch training across GPUs with minimal changes"
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sidebar_label: "Accelerate"
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description: "Run PyTorch training across GPUs with minimal changes"
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---
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{/* This page is auto-generated from the skill's SKILL.md by website/scripts/generate-skill-docs.py. Edit the source SKILL.md, not this page. */}
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# Accelerate
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Run PyTorch training across GPUs with minimal changes.
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## Skill metadata
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| | |
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| Source | Optional — install with `hermes skills install official/mlops/accelerate` |
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| Path | `optional-skills/mlops\accelerate` |
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| Version | `1.0.1` |
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| Author | Orchestra Research |
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| License | MIT |
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| Dependencies | `accelerate`, `torch`, `transformers` |
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| Platforms | linux, macos, windows |
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| Tags | `Distributed Training`, `HuggingFace`, `Accelerate`, `DeepSpeed`, `FSDP`, `Mixed Precision`, `PyTorch`, `DDP`, `Unified API`, `Simple` |
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## Reference: full SKILL.md
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:::info
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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.
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:::
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# HuggingFace Accelerate - Unified Distributed Training
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## Quick start
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Accelerate simplifies distributed training to 4 lines of code.
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**Installation**:
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```bash
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pip install accelerate
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```
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**Convert PyTorch script** (4 lines):
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```python
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import torch
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+ from accelerate import Accelerator
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+ accelerator = Accelerator()
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model = torch.nn.Transformer()
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optimizer = torch.optim.Adam(model.parameters())
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dataloader = torch.utils.data.DataLoader(dataset)
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+ model, optimizer, dataloader = accelerator.prepare(model, optimizer, dataloader)
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for batch in dataloader:
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optimizer.zero_grad()
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loss = model(batch)
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- loss.backward()
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+ accelerator.backward(loss)
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optimizer.step()
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```
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**Run** (single command):
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```bash
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accelerate launch train.py
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```
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## Common workflows
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### Workflow 1: From single GPU to multi-GPU
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**Original script**:
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```python
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# train.py
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import torch
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model = torch.nn.Linear(10, 2).to('cuda')
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optimizer = torch.optim.Adam(model.parameters())
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dataloader = torch.utils.data.DataLoader(dataset, batch_size=32)
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for epoch in range(10):
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for batch in dataloader:
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batch = batch.to('cuda')
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optimizer.zero_grad()
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loss = model(batch).mean()
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loss.backward()
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optimizer.step()
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```
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**With Accelerate** (4 lines added):
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```python
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# train.py
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import torch
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from accelerate import Accelerator # +1
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accelerator = Accelerator() # +2
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model = torch.nn.Linear(10, 2)
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optimizer = torch.optim.Adam(model.parameters())
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dataloader = torch.utils.data.DataLoader(dataset, batch_size=32)
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model, optimizer, dataloader = accelerator.prepare(model, optimizer, dataloader) # +3
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for epoch in range(10):
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for batch in dataloader:
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# No .to('cuda') needed - automatic!
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optimizer.zero_grad()
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loss = model(batch).mean()
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accelerator.backward(loss) # +4
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optimizer.step()
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```
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**Configure** (interactive):
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```bash
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accelerate config
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```
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**Questions**:
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- Which machine? (single/multi GPU/TPU/CPU)
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- How many machines? (1)
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- Mixed precision? (no/fp16/bf16/fp8)
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- DeepSpeed? (no/yes)
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**Launch** (works on any setup):
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```bash
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# Single GPU
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accelerate launch train.py
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# Multi-GPU (8 GPUs)
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accelerate launch --multi_gpu --num_processes 8 train.py
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# Multi-node
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accelerate launch --multi_gpu --num_processes 16 \
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--num_machines 2 --machine_rank 0 \
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--main_process_ip $MASTER_ADDR \
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train.py
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```
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### Workflow 2: Mixed precision training
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**Enable FP16/BF16**:
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```python
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from accelerate import Accelerator
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# FP16 (with gradient scaling)
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accelerator = Accelerator(mixed_precision='fp16')
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# BF16 (no scaling, more stable)
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accelerator = Accelerator(mixed_precision='bf16')
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# FP8 (H100+)
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accelerator = Accelerator(mixed_precision='fp8')
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model, optimizer, dataloader = accelerator.prepare(model, optimizer, dataloader)
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# Everything else is automatic!
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for batch in dataloader:
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with accelerator.autocast(): # Optional, done automatically
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loss = model(batch)
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accelerator.backward(loss)
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```
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### Workflow 3: DeepSpeed ZeRO integration
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**Enable DeepSpeed ZeRO-2** (pass a `DeepSpeedPlugin`, not a raw dict):
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```python
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from accelerate import Accelerator, DeepSpeedPlugin
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deepspeed_plugin = DeepSpeedPlugin(
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zero_stage=2, # ZeRO-2
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offload_optimizer_device="none", # or "cpu" to offload
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gradient_accumulation_steps=4,
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)
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accelerator = Accelerator(
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mixed_precision='bf16',
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deepspeed_plugin=deepspeed_plugin, # DeepSpeedPlugin instance (or dict[str, DeepSpeedPlugin])
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)
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# Same code as before!
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model, optimizer, dataloader = accelerator.prepare(model, optimizer, dataloader)
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```
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**Or point at a full DeepSpeed JSON config via the plugin**:
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```python
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from accelerate import Accelerator, DeepSpeedPlugin
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# hf_ds_config accepts a path to a DeepSpeed config JSON (or a dict)
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deepspeed_plugin = DeepSpeedPlugin(hf_ds_config="ds_config.json")
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accelerator = Accelerator(mixed_precision='bf16', deepspeed_plugin=deepspeed_plugin)
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```
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**ds_config.json** (a raw DeepSpeed config — passed via the plugin, NOT via `--config_file`):
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```json
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{
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"fp16": {"enabled": false},
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"bf16": {"enabled": true},
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"zero_optimization": {
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"stage": 2,
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"offload_optimizer": {"device": "cpu"},
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"allgather_bucket_size": 5e8,
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"reduce_bucket_size": 5e8
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}
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}
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```
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**Or via interactive config**:
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```bash
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accelerate config
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# Select: DeepSpeed → ZeRO-2
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# This writes an accelerate YAML config (default: ~/.cache/huggingface/accelerate/default_config.yaml)
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```
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**Launch** (`--config_file` expects an accelerate YAML, not a raw DeepSpeed JSON):
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```bash
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# Uses the default accelerate config written by `accelerate config`
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accelerate launch train.py
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# Or point at a specific accelerate YAML
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accelerate launch --config_file accelerate_deepspeed.yaml train.py
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```
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### Workflow 4: FSDP (Fully Sharded Data Parallel)
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**Enable FSDP**:
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```python
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from accelerate import Accelerator, FullyShardedDataParallelPlugin
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fsdp_plugin = FullyShardedDataParallelPlugin(
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sharding_strategy="FULL_SHARD", # ZeRO-3 equivalent
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auto_wrap_policy="transformer_based_wrap", # valid: transformer_based_wrap | size_based_wrap | no_wrap
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cpu_offload=False
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)
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accelerator = Accelerator(
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mixed_precision='bf16',
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fsdp_plugin=fsdp_plugin
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)
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model, optimizer, dataloader = accelerator.prepare(model, optimizer, dataloader)
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```
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**Or via config**:
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```bash
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accelerate config
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# Select: FSDP → Full Shard → No CPU Offload
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```
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### Workflow 5: Gradient accumulation
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**Accumulate gradients**:
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```python
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from accelerate import Accelerator
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accelerator = Accelerator(gradient_accumulation_steps=4)
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model, optimizer, dataloader = accelerator.prepare(model, optimizer, dataloader)
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for batch in dataloader:
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with accelerator.accumulate(model): # Handles accumulation
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optimizer.zero_grad()
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loss = model(batch)
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accelerator.backward(loss)
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optimizer.step()
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```
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**Effective batch size**: `batch_size * num_gpus * gradient_accumulation_steps`
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## When to use vs alternatives
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**Use Accelerate when**:
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- Want simplest distributed training
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- Need single script for any hardware
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- Use HuggingFace ecosystem
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- Want flexibility (DDP/DeepSpeed/FSDP/Megatron)
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- Need quick prototyping
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**Key advantages**:
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- **4 lines**: Minimal code changes
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- **Unified API**: Same code for DDP, DeepSpeed, FSDP, Megatron
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- **Automatic**: Device placement, mixed precision, sharding
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- **Interactive config**: No manual launcher setup
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- **Single launch**: Works everywhere
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**Use alternatives instead**:
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- **PyTorch Lightning**: Need callbacks, high-level abstractions
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- **Ray Train**: Multi-node orchestration, hyperparameter tuning
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- **DeepSpeed**: Direct API control, advanced features
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- **Raw DDP**: Maximum control, minimal abstraction
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## Common issues
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**Issue: Wrong device placement**
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Don't manually move to device:
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```python
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# WRONG
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batch = batch.to('cuda')
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# CORRECT
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# Accelerate handles it automatically after prepare()
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```
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**Issue: Gradient accumulation not working**
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Use context manager:
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```python
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# CORRECT
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with accelerator.accumulate(model):
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optimizer.zero_grad()
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accelerator.backward(loss)
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optimizer.step()
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```
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**Issue: Checkpointing in distributed**
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Use accelerator methods:
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```python
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# Save only on main process
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if accelerator.is_main_process:
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accelerator.save_state('checkpoint/')
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# Load on all processes
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accelerator.load_state('checkpoint/')
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```
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**Issue: Different results with FSDP**
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Ensure same random seed:
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```python
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from accelerate.utils import set_seed
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set_seed(42)
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```
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## Advanced topics
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**Megatron integration**: See [references/megatron-integration.md](https://github.com/NousResearch/hermes-agent/blob/main/optional-skills/mlops\accelerate/references/megatron-integration.md) for tensor parallelism, pipeline parallelism, and sequence parallelism setup.
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**Custom plugins**: See [references/custom-plugins.md](https://github.com/NousResearch/hermes-agent/blob/main/optional-skills/mlops\accelerate/references/custom-plugins.md) for creating custom distributed plugins and advanced configuration.
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**Performance tuning**: See [references/performance.md](https://github.com/NousResearch/hermes-agent/blob/main/optional-skills/mlops\accelerate/references/performance.md) for profiling, memory optimization, and best practices.
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## Hardware requirements
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- **CPU**: Works (slow)
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- **Single GPU**: Works
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- **Multi-GPU**: DDP (default), DeepSpeed, or FSDP
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- **Multi-node**: DDP, DeepSpeed, FSDP, Megatron
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- **TPU**: Supported
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- **Apple MPS**: Supported
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**Launcher requirements**:
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- **DDP**: `torch.distributed.run` (built-in)
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- **DeepSpeed**: `deepspeed` (pip install deepspeed)
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- **FSDP**: PyTorch 1.12+ (built-in)
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- **Megatron**: Custom setup
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## Resources
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- Docs: https://huggingface.co/docs/accelerate
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- GitHub: https://github.com/huggingface/accelerate
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- Version: 1.11.0+
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- Tutorial: "Accelerate your scripts"
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- Examples: https://github.com/huggingface/accelerate/tree/main/examples
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- Used by: HuggingFace Transformers, TRL, PEFT, all HF libraries
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