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Vendor nanoGPT model/train/configurator verbatim

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Copied unmodified from karpathy/nanoGPT @ 3adf61e154c3fe3fca428ad6bc3818b27a3b8291
(MIT licence). Later commits show every change made on top.

Claude-Session: https://claude.ai/code/session_01S8KN7NuUCm8nXLmy6eDuVv
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Cormac Shannon committed 2026-10-28 18:01:29 +00:00
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06-experiments/nanogpt/train.py
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"""
This training script can be run both on a single gpu in debug mode,
and also in a larger training run with distributed data parallel (ddp).
To run on a single GPU, example:
$ python train.py --batch_size=32 --compile=False
To run with DDP on 4 gpus on 1 node, example:
$ torchrun --standalone --nproc_per_node=4 train.py
To run with DDP on 4 gpus across 2 nodes, example:
- Run on the first (master) node with example IP 123.456.123.456:
$ torchrun --nproc_per_node=8 --nnodes=2 --node_rank=0 --master_addr=123.456.123.456 --master_port=1234 train.py
- Run on the worker node:
$ torchrun --nproc_per_node=8 --nnodes=2 --node_rank=1 --master_addr=123.456.123.456 --master_port=1234 train.py
(If your cluster does not have Infiniband interconnect prepend NCCL_IB_DISABLE=1)
"""
import os
import time
import math
import pickle
from contextlib import nullcontext
import numpy as np
import torch
from torch.nn.parallel import DistributedDataParallel as DDP
from torch.distributed import init_process_group, destroy_process_group
from model import GPTConfig, GPT
# -----------------------------------------------------------------------------
# default config values designed to train a gpt2 (124M) on OpenWebText
# I/O
out_dir = 'out'
eval_interval = 2000
log_interval = 1
eval_iters = 200
eval_only = False # if True, script exits right after the first eval
always_save_checkpoint = True # if True, always save a checkpoint after each eval
init_from = 'scratch' # 'scratch' or 'resume' or 'gpt2*'
# wandb logging
wandb_log = False # disabled by default
wandb_project = 'owt'
wandb_run_name = 'gpt2' # 'run' + str(time.time())
# data
dataset = 'openwebtext'
gradient_accumulation_steps = 5 * 8 # used to simulate larger batch sizes
batch_size = 12 # if gradient_accumulation_steps > 1, this is the micro-batch size
block_size = 1024
# model
n_layer = 12
n_head = 12
n_embd = 768
dropout = 0.0 # for pretraining 0 is good, for finetuning try 0.1+
bias = False # do we use bias inside LayerNorm and Linear layers?
# adamw optimizer
learning_rate = 6e-4 # max learning rate
max_iters = 600000 # total number of training iterations
weight_decay = 1e-1
beta1 = 0.9
beta2 = 0.95
grad_clip = 1.0 # clip gradients at this value, or disable if == 0.0
# learning rate decay settings
decay_lr = True # whether to decay the learning rate
warmup_iters = 2000 # how many steps to warm up for
lr_decay_iters = 600000 # should be ~= max_iters per Chinchilla
min_lr = 6e-5 # minimum learning rate, should be ~= learning_rate/10 per Chinchilla
# DDP settings
backend = 'nccl' # 'nccl', 'gloo', etc.
# system
device = 'cuda' # examples: 'cpu', 'cuda', 'cuda:0', 'cuda:1' etc., or try 'mps' on macbooks
dtype = 'bfloat16' if torch.cuda.is_available() and torch.cuda.is_bf16_supported() else 'float16' # 'float32', 'bfloat16', or 'float16', the latter will auto implement a GradScaler
compile = True # use PyTorch 2.0 to compile the model to be faster
# -----------------------------------------------------------------------------
config_keys = [k for k,v in globals().items() if not k.startswith('_') and isinstance(v, (int, float, bool, str))]
exec(open('configurator.py').read()) # overrides from command line or config file
config = {k: globals()[k] for k in config_keys} # will be useful for logging
# -----------------------------------------------------------------------------
# various inits, derived attributes, I/O setup
ddp = int(os.environ.get('RANK', -1)) != -1 # is this a ddp run?
if ddp:
init_process_group(backend=backend)
ddp_rank = int(os.environ['RANK'])
ddp_local_rank = int(os.environ['LOCAL_RANK'])
ddp_world_size = int(os.environ['WORLD_SIZE'])
device = f'cuda:{ddp_local_rank}'
torch.cuda.set_device(device)
master_process = ddp_rank == 0 # this process will do logging, checkpointing etc.
seed_offset = ddp_rank # each process gets a different seed
# world_size number of processes will be training simultaneously, so we can scale
# down the desired gradient accumulation iterations per process proportionally
assert gradient_accumulation_steps % ddp_world_size == 0
gradient_accumulation_steps //= ddp_world_size
else:
# if not ddp, we are running on a single gpu, and one process
master_process = True
seed_offset = 0
ddp_world_size = 1
tokens_per_iter = gradient_accumulation_steps * ddp_world_size * batch_size * block_size
print(f"tokens per iteration will be: {tokens_per_iter:,}")
if master_process:
os.makedirs(out_dir, exist_ok=True)
torch.manual_seed(1337 + seed_offset)
torch.backends.cuda.matmul.allow_tf32 = True # allow tf32 on matmul
torch.backends.cudnn.allow_tf32 = True # allow tf32 on cudnn
device_type = 'cuda' if 'cuda' in device else 'cpu' # for later use in torch.autocast
# note: float16 data type will automatically use a GradScaler
ptdtype = {'float32': torch.float32, 'bfloat16': torch.bfloat16, 'float16': torch.float16}[dtype]
ctx = nullcontext() if device_type == 'cpu' else torch.amp.autocast(device_type=device_type, dtype=ptdtype)
# poor man's data loader
data_dir = os.path.join('data', dataset)
def get_batch(split):
# We recreate np.memmap every batch to avoid a memory leak, as per
# https://stackoverflow.com/questions/45132940/numpy-memmap-memory-usage-want-to-iterate-once/61472122#61472122
if split == 'train':
data = np.memmap(os.path.join(data_dir, 'train.bin'), dtype=np.uint16, mode='r')
else:
data = np.memmap(os.path.join(data_dir, 'val.bin'), dtype=np.uint16, mode='r')
ix = torch.randint(len(data) - block_size, (batch_size,))
x = torch.stack([torch.from_numpy((data[i:i+block_size]).astype(np.int64)) for i in ix])
y = torch.stack([torch.from_numpy((data[i+1:i+1+block_size]).astype(np.int64)) for i in ix])
if device_type == 'cuda':
# pin arrays x,y, which allows us to move them to GPU asynchronously (non_blocking=True)
x, y = x.pin_memory().to(device, non_blocking=True), y.pin_memory().to(device, non_blocking=True)
else:
x, y = x.to(device), y.to(device)
return x, y
# init these up here, can override if init_from='resume' (i.e. from a checkpoint)
iter_num = 0
best_val_loss = 1e9
# attempt to derive vocab_size from the dataset
meta_path = os.path.join(data_dir, 'meta.pkl')
meta_vocab_size = None
if os.path.exists(meta_path):
with open(meta_path, 'rb') as f:
meta = pickle.load(f)
meta_vocab_size = meta['vocab_size']
print(f"found vocab_size = {meta_vocab_size} (inside {meta_path})")
# model init
model_args = dict(n_layer=n_layer, n_head=n_head, n_embd=n_embd, block_size=block_size,
bias=bias, vocab_size=None, dropout=dropout) # start with model_args from command line
if init_from == 'scratch':
# init a new model from scratch
print("Initializing a new model from scratch")
# determine the vocab size we'll use for from-scratch training
if meta_vocab_size is None:
print("defaulting to vocab_size of GPT-2 to 50304 (50257 rounded up for efficiency)")
model_args['vocab_size'] = meta_vocab_size if meta_vocab_size is not None else 50304
gptconf = GPTConfig(**model_args)
model = GPT(gptconf)
elif init_from == 'resume':
print(f"Resuming training from {out_dir}")
# resume training from a checkpoint.
ckpt_path = os.path.join(out_dir, 'ckpt.pt')
checkpoint = torch.load(ckpt_path, map_location=device)
checkpoint_model_args = checkpoint['model_args']
# force these config attributes to be equal otherwise we can't even resume training
# the rest of the attributes (e.g. dropout) can stay as desired from command line
for k in ['n_layer', 'n_head', 'n_embd', 'block_size', 'bias', 'vocab_size']:
model_args[k] = checkpoint_model_args[k]
# create the model
gptconf = GPTConfig(**model_args)
model = GPT(gptconf)
state_dict = checkpoint['model']
# fix the keys of the state dictionary :(
# honestly no idea how checkpoints sometimes get this prefix, have to debug more
unwanted_prefix = '_orig_mod.'
for k,v in list(state_dict.items()):
if k.startswith(unwanted_prefix):
state_dict[k[len(unwanted_prefix):]] = state_dict.pop(k)
model.load_state_dict(state_dict)
iter_num = checkpoint['iter_num']
best_val_loss = checkpoint['best_val_loss']
elif init_from.startswith('gpt2'):
print(f"Initializing from OpenAI GPT-2 weights: {init_from}")
# initialize from OpenAI GPT-2 weights
override_args = dict(dropout=dropout)
model = GPT.from_pretrained(init_from, override_args)
# read off the created config params, so we can store them into checkpoint correctly
for k in ['n_layer', 'n_head', 'n_embd', 'block_size', 'bias', 'vocab_size']:
model_args[k] = getattr(model.config, k)
# crop down the model block size if desired, using model surgery
if block_size < model.config.block_size:
model.crop_block_size(block_size)
model_args['block_size'] = block_size # so that the checkpoint will have the right value
model.to(device)
# initialize a GradScaler. If enabled=False scaler is a no-op
scaler = torch.cuda.amp.GradScaler(enabled=(dtype == 'float16'))
# optimizer
optimizer = model.configure_optimizers(weight_decay, learning_rate, (beta1, beta2), device_type)
if init_from == 'resume':
optimizer.load_state_dict(checkpoint['optimizer'])
checkpoint = None # free up memory
# compile the model
if compile:
print("compiling the model... (takes a ~minute)")
unoptimized_model = model
model = torch.compile(model) # requires PyTorch 2.0
# wrap model into DDP container
if ddp:
model = DDP(model, device_ids=[ddp_local_rank])
# helps estimate an arbitrarily accurate loss over either split using many batches
@torch.no_grad()
def estimate_loss():
out = {}
model.eval()
for split in ['train', 'val']:
losses = torch.zeros(eval_iters)
for k in range(eval_iters):
X, Y = get_batch(split)
with ctx:
logits, loss = model(X, Y)
losses[k] = loss.item()
out[split] = losses.mean()
model.train()
return out
# learning rate decay scheduler (cosine with warmup)
def get_lr(it):
# 1) linear warmup for warmup_iters steps
if it < warmup_iters:
return learning_rate * (it + 1) / (warmup_iters + 1)
# 2) if it > lr_decay_iters, return min learning rate
if it > lr_decay_iters:
return min_lr
# 3) in between, use cosine decay down to min learning rate
decay_ratio = (it - warmup_iters) / (lr_decay_iters - warmup_iters)
assert 0 <= decay_ratio <= 1
coeff = 0.5 * (1.0 + math.cos(math.pi * decay_ratio)) # coeff ranges 0..1
return min_lr + coeff * (learning_rate - min_lr)
# logging
if wandb_log and master_process:
import wandb
wandb.init(project=wandb_project, name=wandb_run_name, config=config)
# training loop
X, Y = get_batch('train') # fetch the very first batch
t0 = time.time()
local_iter_num = 0 # number of iterations in the lifetime of this process
raw_model = model.module if ddp else model # unwrap DDP container if needed
running_mfu = -1.0
while True:
# determine and set the learning rate for this iteration
lr = get_lr(iter_num) if decay_lr else learning_rate
for param_group in optimizer.param_groups:
param_group['lr'] = lr
# evaluate the loss on train/val sets and write checkpoints
if iter_num % eval_interval == 0 and master_process:
losses = estimate_loss()
print(f"step {iter_num}: train loss {losses['train']:.4f}, val loss {losses['val']:.4f}")
if wandb_log:
wandb.log({
"iter": iter_num,
"train/loss": losses['train'],
"val/loss": losses['val'],
"lr": lr,
"mfu": running_mfu*100, # convert to percentage
})
if losses['val'] < best_val_loss or always_save_checkpoint:
best_val_loss = losses['val']
if iter_num > 0:
checkpoint = {
'model': raw_model.state_dict(),
'optimizer': optimizer.state_dict(),
'model_args': model_args,
'iter_num': iter_num,
'best_val_loss': best_val_loss,
'config': config,
}
print(f"saving checkpoint to {out_dir}")
torch.save(checkpoint, os.path.join(out_dir, 'ckpt.pt'))
if iter_num == 0 and eval_only:
break
# forward backward update, with optional gradient accumulation to simulate larger batch size
# and using the GradScaler if data type is float16
for micro_step in range(gradient_accumulation_steps):
if ddp:
# in DDP training we only need to sync gradients at the last micro step.
# the official way to do this is with model.no_sync() context manager, but
# I really dislike that this bloats the code and forces us to repeat code
# looking at the source of that context manager, it just toggles this variable
model.require_backward_grad_sync = (micro_step == gradient_accumulation_steps - 1)
with ctx:
logits, loss = model(X, Y)
loss = loss / gradient_accumulation_steps # scale the loss to account for gradient accumulation
# immediately async prefetch next batch while model is doing the forward pass on the GPU
X, Y = get_batch('train')
# backward pass, with gradient scaling if training in fp16
scaler.scale(loss).backward()
# clip the gradient
if grad_clip != 0.0:
scaler.unscale_(optimizer)
torch.nn.utils.clip_grad_norm_(model.parameters(), grad_clip)
# step the optimizer and scaler if training in fp16
scaler.step(optimizer)
scaler.update()
# flush the gradients as soon as we can, no need for this memory anymore
optimizer.zero_grad(set_to_none=True)
# timing and logging
t1 = time.time()
dt = t1 - t0
t0 = t1
if iter_num % log_interval == 0 and master_process:
# get loss as float. note: this is a CPU-GPU sync point
# scale up to undo the division above, approximating the true total loss (exact would have been a sum)
lossf = loss.item() * gradient_accumulation_steps
if local_iter_num >= 5: # let the training loop settle a bit
mfu = raw_model.estimate_mfu(batch_size * gradient_accumulation_steps, dt)
running_mfu = mfu if running_mfu == -1.0 else 0.9*running_mfu + 0.1*mfu
print(f"iter {iter_num}: loss {lossf:.4f}, time {dt*1000:.2f}ms, mfu {running_mfu*100:.2f}%")
iter_num += 1
local_iter_num += 1
# termination conditions
if iter_num > max_iters:
break
if ddp:
destroy_process_group()