LLMs-from-scratch/ch05/10_llm-training-speed/02_opt_multi_gpu_ddp.py
Matthew Hernandez 83c76891fc
Fix issue 724: unused args (#726)
* Fix issue 724: unused args

* Update 02_opt_multi_gpu_ddp.py
2025-07-08 06:37:39 -05:00

607 lines
21 KiB
Python

# Copyright (c) Sebastian Raschka under Apache License 2.0 (see LICENSE.txt).
# Source for "Build a Large Language Model From Scratch"
# - https://www.manning.com/books/build-a-large-language-model-from-scratch
# Code: https://github.com/rasbt/LLMs-from-scratch
import os
import time
import urllib.request
import matplotlib.pyplot as plt
import torch
import torch.nn as nn
from torch.utils.data import Dataset, DataLoader
import tiktoken
# NEW imports (see Appendix A):
import platform
from torch.utils.data.distributed import DistributedSampler
from torch.nn.parallel import DistributedDataParallel as DDP
from torch.distributed import init_process_group, destroy_process_group
# NEW: function to initialize a distributed process group (1 process / GPU)
# this allows communication among processes
# (see Appendix A):
def ddp_setup(rank, world_size):
"""
Arguments:
rank: a unique process ID
world_size: total number of processes in the group
"""
# Only set MASTER_ADDR and MASTER_PORT if not already defined by torchrun
if "MASTER_ADDR" not in os.environ:
os.environ["MASTER_ADDR"] = "localhost"
if "MASTER_PORT" not in os.environ:
os.environ["MASTER_PORT"] = "12345"
# initialize process group
if platform.system() == "Windows":
# Disable libuv because PyTorch for Windows isn't built with support
os.environ["USE_LIBUV"] = "0"
# Windows users may have to use "gloo" instead of "nccl" as backend
# gloo: Facebook Collective Communication Library
init_process_group(backend="gloo", rank=rank, world_size=world_size)
else:
# nccl: NVIDIA Collective Communication Library
init_process_group(backend="nccl", rank=rank, world_size=world_size)
torch.cuda.set_device(rank)
#####################################
# Chapter 2
#####################################
class GPTDatasetV1(Dataset):
def __init__(self, txt, tokenizer, max_length, stride):
self.input_ids = []
self.target_ids = []
# Tokenize the entire text
token_ids = tokenizer.encode(txt, allowed_special={"<|endoftext|>"})
# Use a sliding window to chunk the book into overlapping sequences of max_length
for i in range(0, len(token_ids) - max_length, stride):
input_chunk = token_ids[i:i + max_length]
target_chunk = token_ids[i + 1: i + max_length + 1]
self.input_ids.append(torch.tensor(input_chunk))
self.target_ids.append(torch.tensor(target_chunk))
def __len__(self):
return len(self.input_ids)
def __getitem__(self, idx):
return self.input_ids[idx], self.target_ids[idx]
# NEW: Modify to set shuffle=False and use a sampler
# (See Appendix A):
def create_dataloader_v1(txt, batch_size=4, max_length=256,
stride=128, drop_last=True, num_workers=0):
# Initialize the tokenizer
tokenizer = tiktoken.get_encoding("gpt2")
# Create dataset
dataset = GPTDatasetV1(txt, tokenizer, max_length, stride)
# Create dataloader
dataloader = DataLoader(
dataset=dataset,
batch_size=batch_size,
shuffle=False, # NEW: False because of DistributedSampler below
drop_last=drop_last,
num_workers=num_workers,
pin_memory=True,
# NEW: chunk batches across GPUs without overlapping samples:
sampler=DistributedSampler(dataset) # NEW
)
return dataloader
#####################################
# Chapter 3
#####################################
class PyTorchMultiHeadAttention(nn.Module):
def __init__(self, d_in, d_out, num_heads, dropout=0.0, qkv_bias=False):
super().__init__()
assert d_out % num_heads == 0, "d_out is indivisible by num_heads"
self.num_heads = num_heads
self.head_dim = d_out // num_heads
self.d_out = d_out
self.qkv = nn.Linear(d_in, 3 * d_out, bias=qkv_bias)
self.proj = nn.Linear(d_out, d_out)
self.dropout = dropout
def forward(self, x):
batch_size, num_tokens, embed_dim = x.shape
# (b, num_tokens, embed_dim) --> (b, num_tokens, 3 * embed_dim)
qkv = self.qkv(x)
# (b, num_tokens, 3 * embed_dim) --> (b, num_tokens, 3, num_heads, head_dim)
qkv = qkv.view(batch_size, num_tokens, 3, self.num_heads, self.head_dim)
# (b, num_tokens, 3, num_heads, head_dim) --> (3, b, num_heads, num_tokens, head_dim)
qkv = qkv.permute(2, 0, 3, 1, 4)
# (3, b, num_heads, num_tokens, head_dim) -> 3 times (b, num_heads, num_tokens, head_dim)
queries, keys, values = qkv
use_dropout = 0. if not self.training else self.dropout
context_vec = nn.functional.scaled_dot_product_attention(
queries, keys, values, attn_mask=None, dropout_p=use_dropout, is_causal=True)
# Combine heads, where self.d_out = self.num_heads * self.head_dim
context_vec = context_vec.transpose(1, 2).contiguous().view(batch_size, num_tokens, self.d_out)
context_vec = self.proj(context_vec)
return context_vec
#####################################
# Chapter 4
#####################################
class FeedForward(nn.Module):
def __init__(self, cfg):
super().__init__()
self.layers = nn.Sequential(
nn.Linear(cfg["emb_dim"], 4 * cfg["emb_dim"]),
nn.GELU(approximate="tanh"),
nn.Linear(4 * cfg["emb_dim"], cfg["emb_dim"]),
)
def forward(self, x):
return self.layers(x)
class TransformerBlock(nn.Module):
def __init__(self, cfg):
super().__init__()
self.att = PyTorchMultiHeadAttention(
d_in=cfg["emb_dim"],
d_out=cfg["emb_dim"],
num_heads=cfg["n_heads"],
dropout=cfg["drop_rate"],
qkv_bias=cfg["qkv_bias"])
self.ff = FeedForward(cfg)
self.norm1 = nn.LayerNorm(cfg["emb_dim"])
self.norm2 = nn.LayerNorm(cfg["emb_dim"])
self.drop_shortcut = nn.Dropout(cfg["drop_rate"])
def forward(self, x):
# Shortcut connection for attention block
shortcut = x
x = self.norm1(x)
x = self.att(x) # Shape [batch_size, num_tokens, emb_size]
x = self.drop_shortcut(x)
x = x + shortcut # Add the original input back
# Shortcut connection for feed-forward block
shortcut = x
x = self.norm2(x)
x = self.ff(x)
x = self.drop_shortcut(x)
x = x + shortcut # Add the original input back
return x
class GPTModel(nn.Module):
def __init__(self, cfg):
super().__init__()
self.tok_emb = nn.Embedding(cfg["vocab_size"], cfg["emb_dim"])
self.pos_emb = nn.Embedding(cfg["context_length"], cfg["emb_dim"])
self.drop_emb = nn.Dropout(cfg["drop_rate"])
self.trf_blocks = nn.Sequential(
*[TransformerBlock(cfg) for _ in range(cfg["n_layers"])])
self.final_norm = nn.LayerNorm(cfg["emb_dim"])
self.out_head = nn.Linear(cfg["emb_dim"], cfg["vocab_size"], bias=False)
def forward(self, in_idx):
batch_size, seq_len = in_idx.shape
tok_embeds = self.tok_emb(in_idx)
pos_embeds = self.pos_emb(torch.arange(seq_len, device=in_idx.device))
x = tok_embeds + pos_embeds # Shape [batch_size, num_tokens, emb_size]
x = self.drop_emb(x)
x = self.trf_blocks(x)
x = self.final_norm(x)
logits = self.out_head(x)
return logits
def generate_text_simple(model, idx, max_new_tokens, context_size):
# idx is (B, T) array of indices in the current context
for _ in range(max_new_tokens):
# Crop current context if it exceeds the supported context size
# E.g., if LLM supports only 5 tokens, and the context size is 10
# then only the last 5 tokens are used as context
idx_cond = idx[:, -context_size:]
# Get the predictions
with torch.no_grad():
logits = model(idx_cond)
# Focus only on the last time step
# (batch, n_token, vocab_size) becomes (batch, vocab_size)
logits = logits[:, -1, :]
# Get the idx of the vocab entry with the highest logits value
idx_next = torch.argmax(logits, dim=-1, keepdim=True) # (batch, 1)
# Append sampled index to the running sequence
idx = torch.cat((idx, idx_next), dim=1) # (batch, n_tokens+1)
return idx
#####################################
# Chapter 5
#####################################
def text_to_token_ids(text, tokenizer):
encoded = tokenizer.encode(text)
encoded_tensor = torch.tensor(encoded).unsqueeze(0) # add batch dimension
return encoded_tensor
def token_ids_to_text(token_ids, tokenizer):
flat = token_ids.squeeze(0) # remove batch dimension
return tokenizer.decode(flat.tolist())
def calc_loss_batch(input_batch, target_batch, model, device):
input_batch, target_batch = input_batch.to(device), target_batch.to(device)
logits = model(input_batch)
loss = torch.nn.functional.cross_entropy(logits.flatten(0, 1), target_batch.flatten())
return loss
def calc_loss_loader(data_loader, model, device, num_batches=None):
total_loss = 0.
if len(data_loader) == 0:
return float("nan")
elif num_batches is None:
num_batches = len(data_loader)
else:
num_batches = min(num_batches, len(data_loader))
for i, (input_batch, target_batch) in enumerate(data_loader):
if i < num_batches:
loss = calc_loss_batch(input_batch, target_batch, model, device)
total_loss += loss.item()
else:
break
return total_loss / num_batches
def evaluate_model(model, train_loader, val_loader, device, eval_iter):
model.eval()
with torch.no_grad():
train_loss = calc_loss_loader(train_loader, model, device, num_batches=eval_iter)
val_loss = calc_loss_loader(val_loader, model, device, num_batches=eval_iter)
model.train()
return train_loss, val_loss
def generate_and_print_sample(model, device, start_context):
model.eval()
# NEW: Modify for DDP
context_size = model.module.pos_emb.weight.shape[0] if isinstance(model, DDP) else model.pos_emb.weight.shape[0]
encoded = text_to_token_ids(start_context, tiktoken.get_encoding("gpt2")).to(device)
with torch.no_grad():
token_ids = generate_text_simple(
model=model, idx=encoded,
max_new_tokens=50, context_size=context_size
)
decoded_text = token_ids_to_text(token_ids, tiktoken.get_encoding("gpt2"))
print(decoded_text.replace("\n", " ")) # Compact print format
model.train()
def train_model_simple_with_timing(model, train_loader, val_loader, optimizer, device,
num_epochs, eval_freq, eval_iter, start_context):
train_losses, val_losses, track_tokens = [], [], []
total_tokens, global_step, last_tokens = 0, -1, 0
# NEW: Determine the current rank (default to 0 if not distributed)
rank = torch.distributed.get_rank() if torch.distributed.is_initialized() else 0
# world_size = torch.distributed.get_world_size() if torch.distributed.is_initialized() else 1
# Variables for cumulative average tokens/sec
cumulative_tokens, cumulative_time = 0.0, 0.0
# CUDA-specific timing setup
use_cuda = device.type == "cuda"
if use_cuda:
t_start = torch.cuda.Event(enable_timing=True)
t_end = torch.cuda.Event(enable_timing=True)
torch.cuda.synchronize() # Ensure all prior CUDA operations are done
t_start.record() # Start the timer for the first interval
else:
t0 = time.time() # Start the timer for the first interval
# Main training loop
for epoch in range(num_epochs):
# NEW: set epoch for DistributedSampler so each process gets a unique shuffle order
if isinstance(train_loader.sampler, DistributedSampler):
train_loader.sampler.set_epoch(epoch)
model.train()
for inp_batch, tgt_batch in train_loader:
optimizer.zero_grad()
global_step += 1
# Forward and backward pass
loss = calc_loss_batch(inp_batch, tgt_batch, model, device)
loss.backward()
optimizer.step()
total_tokens += inp_batch.numel()
# At evaluation intervals, measure elapsed time and tokens per second
if global_step % eval_freq == 0:
# End timing for the current interval
if use_cuda:
t_end.record()
torch.cuda.synchronize() # Wait for all CUDA ops to complete.
elapsed = t_start.elapsed_time(t_end) / 1000 # Convert ms to seconds
t_start.record() # Reset timer for the next interval
else:
elapsed = time.time() - t0
t0 = time.time() # Reset timer for the next interval
# Calculate local tokens processed during this interval
local_interval = total_tokens - last_tokens
last_tokens = total_tokens
# Aggregate the tokens processed over all devices
local_tensor = torch.tensor([local_interval], device=device, dtype=torch.float)
global_tensor = local_tensor.clone()
torch.distributed.all_reduce(global_tensor, op=torch.distributed.ReduceOp.SUM)
global_interval = global_tensor.item()
# Global tokens per second for this interval
global_tps = global_interval / elapsed if elapsed > 0 else 0
# Update cumulative tokens (local) and aggregate globally
cumulative_tokens += local_interval
local_cum_tensor = torch.tensor([cumulative_tokens], device=device, dtype=torch.float)
global_cum_tensor = local_cum_tensor.clone()
torch.distributed.all_reduce(global_cum_tensor, op=torch.distributed.ReduceOp.SUM)
global_cumulative_tokens = global_cum_tensor.item()
cumulative_time += elapsed
global_avg_tps = global_cumulative_tokens / cumulative_time if cumulative_time > 0 else 0
# Evaluate model performance (this may add overhead)
train_loss, val_loss = evaluate_model(model, train_loader, val_loader, device, eval_iter)
train_losses.append(train_loss)
val_losses.append(val_loss)
track_tokens.append(total_tokens)
# NEW: Only print logs once per GPU (choosing the rank 0 GPU)
if rank == 0:
print(f"Ep {epoch+1}, Step {global_step:06d}, "
f"Train: {train_loss:.3f}, Val: {val_loss:.3f}, "
f"Step tok/sec: {round(global_tps)}, Global avg tok/sec: {round(global_avg_tps)}")
# NEW Only rank 0 prints the generated sample and memory usage stats
if rank == 0 and epoch % 5 == 0:
generate_and_print_sample(model, device, start_context)
# Memory stats
if torch.cuda.is_available():
current_device = torch.cuda.current_device()
allocated = torch.cuda.memory_allocated(current_device) / 1024**3 # Convert to GB
reserved = torch.cuda.memory_reserved(current_device) / 1024**3 # Convert to GB
print(f"\nAllocated memory: {allocated:.4f} GB")
print(f"Reserved memory: {reserved:.4f} GB\n")
return train_losses, val_losses, track_tokens
def plot_losses(epochs_seen, tokens_seen, train_losses, val_losses):
fig, ax1 = plt.subplots()
# Plot training and validation loss against epochs
ax1.plot(epochs_seen, train_losses, label="Training loss")
ax1.plot(epochs_seen, val_losses, linestyle="-.", label="Validation loss")
ax1.set_xlabel("Epochs")
ax1.set_ylabel("Loss")
ax1.legend(loc="upper right")
# Create a second x-axis for tokens seen
ax2 = ax1.twiny() # Create a second x-axis that shares the same y-axis
ax2.plot(tokens_seen, train_losses, alpha=0) # Invisible plot for aligning ticks
ax2.set_xlabel("Tokens seen")
fig.tight_layout() # Adjust layout to make room
# plt.show()
#####################################
# Main function calls
#####################################
# NEW: Add rank and world_size
def main(gpt_config, settings, rank, world_size):
ddp_setup(rank, world_size) # NEW: initialize process groups
device = torch.device("cuda", rank)
torch.manual_seed(123)
# NEW: Print info only on 1 GPU
if rank == 0:
print(f"PyTorch version: {torch.__version__}")
if torch.cuda.is_available():
print(f"CUDA version: {torch.version.cuda}")
capability = torch.cuda.get_device_capability()
if capability[0] >= 7: # Volta (7.0+), Turing (7.5+), Ampere (8.0+), Hopper (9.0+)
torch.set_float32_matmul_precision("high")
print("Uses tensor cores")
else:
print("Tensor cores not supported on this GPU. Using default precision.")
print()
##############################
# Download data if necessary
##############################
file_path = "middlemarch.txt"
url = "https://www.gutenberg.org/cache/epub/145/pg145.txt"
# NEW: Only download 1 time
if rank == 0:
if not os.path.exists(file_path):
with urllib.request.urlopen(url) as response:
text_data = response.read().decode('utf-8')
with open(file_path, "w", encoding="utf-8") as file:
file.write(text_data)
# NEW: All processes wait until rank 0 is done, using the GPU index.
torch.distributed.barrier(device_ids=[device.index])
with open(file_path, "r", encoding="utf-8") as file:
text_data = file.read()
##############################
# Initialize model
##############################
model = GPTModel(gpt_config)
model = torch.compile(model)
model = model.to(device)
model = model.to(torch.bfloat16)
# NEW: Wrap model with DDP
model = DDP(model, device_ids=[rank])
optimizer = torch.optim.AdamW(
model.parameters(), lr=settings["learning_rate"], weight_decay=settings["weight_decay"],
fused=True
)
##############################
# Set up dataloaders
##############################
# Train/validation ratio
train_ratio = 0.90
split_idx = int(train_ratio * len(text_data))
train_loader = create_dataloader_v1(
text_data[:split_idx],
batch_size=settings["batch_size"],
max_length=gpt_config["context_length"],
stride=gpt_config["context_length"],
drop_last=True,
num_workers=4
)
val_loader = create_dataloader_v1(
text_data[split_idx:],
batch_size=settings["batch_size"],
max_length=gpt_config["context_length"],
stride=gpt_config["context_length"],
drop_last=False,
num_workers=4
)
##############################
# Train model
##############################
train_losses, val_losses, tokens_seen = train_model_simple_with_timing(
model=model,
train_loader=train_loader,
val_loader=val_loader,
optimizer=optimizer,
device=device,
num_epochs=settings["num_epochs"],
eval_freq=5,
eval_iter=1,
start_context="Every effort moves you",
)
# NEW: Clean up distributed processes
destroy_process_group()
return train_losses, val_losses, tokens_seen, model
if __name__ == "__main__":
# NEW: Extract rank and world size from environment variables
if "WORLD_SIZE" in os.environ:
world_size = int(os.environ["WORLD_SIZE"])
else:
world_size = 1
if "LOCAL_RANK" in os.environ:
rank = int(os.environ["LOCAL_RANK"])
elif "RANK" in os.environ:
rank = int(os.environ["RANK"])
else:
rank = 0
GPT_CONFIG_124M = {
"vocab_size": 50304, # Vocabulary size
"context_length": 1024, # Input tokens per training example
"emb_dim": 768, # Embedding dimension
"n_heads": 12, # Number of attention heads
"n_layers": 12, # Number of layers
"drop_rate": 0.1, # Dropout rate
"qkv_bias": False # Query-key-value bias
}
OTHER_SETTINGS = {
"learning_rate": 5e-4, # * world_size, # NEW: Increase learning rate to account for multiple GPUs
"num_epochs": 50,
"batch_size": 32,
"weight_decay": 0.1
}
###########################
# Initiate training
###########################
train_losses, val_losses, tokens_seen, model = main(
GPT_CONFIG_124M, OTHER_SETTINGS,
rank, world_size # NEW
)
###########################
# After training
###########################
# NEW: Only create 1 plot
if rank == 0:
# Plot results
epochs_tensor = torch.linspace(0, OTHER_SETTINGS["num_epochs"], len(train_losses))
plot_losses(epochs_tensor, tokens_seen, train_losses, val_losses)
plt.savefig("loss.pdf")
# Save and load model
#
# compiled = hasattr(model, "_orig_mod")
# if compiled:
# torch.save(model._orig_mod.state_dict(), "model.pth")
# else:
# torch.save(model.state_dict(), "model.pth")
#
# model = GPTModel(GPT_CONFIG_124M)
# model.load_state_dict(torch.load("model.pth", weights_only=True))