""" Reference code for GPT-2 training and inference. Will save the model weights into files, to be read from C as initialization. References: 1) the official GPT-2 TensorFlow implementation released by OpenAI: https://github.com/openai/gpt-2/blob/master/src/model.py 2) huggingface/transformers PyTorch implementation: https://github.com/huggingface/transformers/blob/main/src/transformers/models/gpt2/modeling_gpt2.py Example launches to only benchmark the speed of bfloat16 compiled GPU training: 1 GPU: python train_gpt2.py --write_tensors=0 --num_iterations=50 --sequence_length=1024 --compile=1 --tensorcores=1 --dtype=bfloat16 you can also turn on flash-attention by appending --flash=1 4 GPU: torchrun --standalone --nproc_per_node=4 train_gpt2.py --write_tensors=0 --num_iterations=50 --sequence_length=1024 --compile=1 --tensorcores=1 --dtype=bfloat16 """ import os import math import struct from contextlib import nullcontext from dataclasses import dataclass import numpy as np import torch import torch.nn as nn from torch.nn import functional as F import torch._inductor.config as config from torch.nn.parallel import DistributedDataParallel as DDP from torch.distributed import init_process_group, destroy_process_group class NewGELU(nn.Module): """Careful there are a few versions of GeLU, this one is the exact one used by OpenAI""" def forward(self, input): return 0.5 * input * (1.0 + torch.tanh(math.sqrt(2.0 / math.pi) * (input + 0.044715 * torch.pow(input, 3.0)))) # using a global to toggle flash-attention FLASH = 0 class CausalSelfAttention(nn.Module): def __init__(self, config): super().__init__() assert config.n_embd % config.n_head == 0 # key, query, value projections for all heads, but in a batch self.c_attn = nn.Linear(config.n_embd, 3 * config.n_embd) # output projection self.c_proj = nn.Linear(config.n_embd, config.n_embd) # regularization self.n_head = config.n_head self.n_embd = config.n_embd # not really a 'bias', more of a mask, but following the OpenAI/HF naming though self.register_buffer("bias", torch.tril(torch.ones(config.block_size, config.block_size)) .view(1, 1, config.block_size, config.block_size)) def forward(self, x): B, T, C = x.size() # batch size, sequence length, embedding dimensionality (n_embd) # calculate query, key, values for all heads in batch and move head forward to be the batch dim qkv = self.c_attn(x) q, k, v = qkv.split(self.n_embd, dim=2) k = k.view(B, T, self.n_head, C // self.n_head).transpose(1, 2) # (B, nh, T, hs) q = q.view(B, T, self.n_head, C // self.n_head).transpose(1, 2) # (B, nh, T, hs) v = v.view(B, T, self.n_head, C // self.n_head).transpose(1, 2) # (B, nh, T, hs) if FLASH: # flashattention y = F.scaled_dot_product_attention(q, k, v, is_causal=True) else: # manual implementation of attention # this materializes the large (T,T) matrix for all the queries and keys att = (q @ k.transpose(-2, -1)) * (1.0 / math.sqrt(k.size(-1))) att = att.masked_fill(self.bias[:,:,:T,:T] == 0, float('-inf')) att = F.softmax(att, dim=-1) y = att @ v # (B, nh, T, T) x (B, nh, T, hs) -> (B, nh, T, hs) y = y.transpose(1, 2).contiguous().view(B, T, C) # re-assemble all head outputs side by side # output projection y = self.c_proj(y) return y class MLP(nn.Module): def __init__(self, config): super().__init__() self.c_fc = nn.Linear(config.n_embd, 4 * config.n_embd) self.gelu = NewGELU() self.c_proj = nn.Linear(4 * config.n_embd, config.n_embd) def forward(self, x): x = self.c_fc(x) x = self.gelu(x) x = self.c_proj(x) return x class Block(nn.Module): def __init__(self, config): super().__init__() self.ln_1 = nn.LayerNorm(config.n_embd) self.attn = CausalSelfAttention(config) self.ln_2 = nn.LayerNorm(config.n_embd) self.mlp = MLP(config) def forward(self, x): x = x + self.attn(self.ln_1(x)) x = x + self.mlp(self.ln_2(x)) return x @dataclass class GPTConfig: block_size: int = 1024 vocab_size: int = 50257 n_layer: int = 12 n_head: int = 12 n_embd: int = 768 class GPT(nn.Module): def __init__(self, config): super().__init__() self.config = config self.transformer = nn.ModuleDict(dict( wte = nn.Embedding(config.vocab_size, config.n_embd), wpe = nn.Embedding(config.block_size, config.n_embd), h = nn.ModuleList([Block(config) for _ in range(config.n_layer)]), ln_f = nn.LayerNorm(config.n_embd), )) self.lm_head = nn.Linear(config.n_embd, config.vocab_size, bias=False) self.transformer.wte.weight = self.lm_head.weight # https://paperswithcode.com/method/weight-tying def forward(self, idx, targets=None): device = idx.device b, t = idx.size() assert t <= self.config.block_size, f"Cannot forward sequence of length {t}, block size is only {self.config.block_size}" pos = torch.arange(0, t, dtype=torch.long, device=device) # shape (t) # forward the GPT model itself tok_emb = self.transformer.wte(idx) # token embeddings of shape (b, t, n_embd) pos_emb = self.transformer.wpe(pos) # position embeddings of shape (t, n_embd) x = tok_emb + pos_emb for block in self.transformer.h: x = block(x) x = self.transformer.ln_f(x) if targets is not None: # if we are given some desired targets also calculate the loss logits = self.lm_head(x) loss = F.cross_entropy(logits.view(-1, logits.size(-1)), targets.view(-1), ignore_index=-1) else: # inference-time mini-optimization: only forward the lm_head on the very last position logits = self.lm_head(x[:, [-1], :]) # note: using list [-1] to preserve the time dim loss = None return logits, loss @classmethod def from_pretrained(cls, model_type): """Loads pretrained GPT-2 model weights from huggingface""" assert model_type in {'gpt2', 'gpt2-medium', 'gpt2-large', 'gpt2-xl'} from transformers import GPT2LMHeadModel print("loading weights from pretrained gpt: %s" % model_type) # n_layer, n_head and n_embd are determined from model_type config_args = { 'gpt2': dict(n_layer=12, n_head=12, n_embd=768), # 124M params 'gpt2-medium': dict(n_layer=24, n_head=16, n_embd=1024), # 350M params 'gpt2-large': dict(n_layer=36, n_head=20, n_embd=1280), # 774M params 'gpt2-xl': dict(n_layer=48, n_head=25, n_embd=1600), # 1558M params }[model_type] config_args['vocab_size'] = 50257 # always 50257 for GPT model checkpoints config_args['block_size'] = 1024 # always 1024 for GPT model checkpoints # create a from-scratch initialized minGPT model config = GPTConfig(**config_args) model = GPT(config) sd = model.state_dict() sd_keys = sd.keys() sd_keys = [k for k in sd_keys if not k.endswith('.attn.bias')] # discard this mask / buffer, not a param # init a huggingface/transformers model model_hf = GPT2LMHeadModel.from_pretrained(model_type) sd_hf = model_hf.state_dict() # copy while ensuring all of the parameters are aligned and match in names and shapes sd_keys_hf = sd_hf.keys() sd_keys_hf = [k for k in sd_keys_hf if not k.endswith('.attn.masked_bias')] # ignore these, just a buffer sd_keys_hf = [k for k in sd_keys_hf if not k.endswith('.attn.bias')] # same, just the mask (buffer) transposed = ['attn.c_attn.weight', 'attn.c_proj.weight', 'mlp.c_fc.weight', 'mlp.c_proj.weight'] # basically the openai checkpoints use a "Conv1D" module, but we only want to use a vanilla Linear # this means that we have to transpose these weights when we import them assert len(sd_keys_hf) == len(sd_keys), f"mismatched keys: {len(sd_keys_hf)} != {len(sd_keys)}" for k in sd_keys_hf: if any(k.endswith(w) for w in transposed): # special treatment for the Conv1D weights we need to transpose assert sd_hf[k].shape[::-1] == sd[k].shape with torch.no_grad(): sd[k].copy_(sd_hf[k].t()) else: # vanilla copy over the other parameters assert sd_hf[k].shape == sd[k].shape with torch.no_grad(): sd[k].copy_(sd_hf[k]) return model @torch.no_grad() def generate(self, idx, max_new_tokens, temperature=1.0, top_k=None): """ Take a conditioning sequence of indices idx (LongTensor of shape (b,t)) and complete the sequence max_new_tokens times, feeding the predictions back into the model each time. Most likely you'll want to make sure to be in model.eval() mode of operation for this. """ for _ in range(max_new_tokens): # if the sequence context is growing too long we must crop it at block_size idx_cond = idx if idx.size(1) <= self.config.block_size else idx[:, -self.config.block_size:] # forward the model to get the logits for the index in the sequence logits, _ = self(idx_cond) # pluck the logits at the final step and scale by desired temperature logits = logits[:, -1, :] / temperature # optionally crop the logits to only the top k options if top_k is not None: v, _ = torch.topk(logits, min(top_k, logits.size(-1))) logits[logits < v[:, [-1]]] = -float('Inf') # apply softmax to convert logits to (normalized) probabilities probs = F.softmax(logits, dim=-1) # sample from the distribution idx_next = torch.multinomial(probs, num_samples=1) # append sampled index to the running sequence and continue idx = torch.cat((idx, idx_next), dim=1) return idx # a few utilities for saving params/grads/activations to files for loading in C def write_fp32(tensor, file): t = tensor.detach().cpu().to(torch.float32) b = t.numpy().tobytes() file.write(b) def write_bf16(tensor, file): t = tensor.detach().cpu().to(torch.bfloat16) # numpy doesn't have bf16 datatype so we have to trick it t = t.view(torch.int16) # trick: reinterpret as int16 b = t.numpy().tobytes() file.write(b) def write_tensors(model_tensors, L, file, dtype): assert dtype in {"float32", "bfloat16"} write_fun = write_fp32 if dtype == "float32" else write_bf16 write_fun(model_tensors["transformer.wte.weight"], file) # (V, C) write_fun(model_tensors["transformer.wpe.weight"], file) # (T, C) for i in range(L): # (L, C) write_fun(model_tensors[f"transformer.h.{i}.ln_1.weight"], file) for i in range(L): # (L, C) write_fun(model_tensors[f"transformer.h.{i}.ln_1.bias"], file) for i in range(L): # (L, 3C, C) write_fun(model_tensors[f"transformer.h.{i}.attn.c_attn.weight"], file) for i in range(L): # (L, 3C) write_fun(model_tensors[f"transformer.h.{i}.attn.c_attn.bias"], file) for i in range(L): # (L, C, C) write_fun(model_tensors[f"transformer.h.{i}.attn.c_proj.weight"], file) for i in range(L): # (L, C) write_fun(model_tensors[f"transformer.h.{i}.attn.c_proj.bias"], file) for i in range(L): # (L, C) write_fun(model_tensors[f"transformer.h.{i}.ln_2.weight"], file) for i in range(L): # (L, C) write_fun(model_tensors[f"transformer.h.{i}.ln_2.bias"], file) for i in range(L): # (L, 4C, C) write_fun(model_tensors[f"transformer.h.{i}.mlp.c_fc.weight"], file) for i in range(L): # (L, 4C) write_fun(model_tensors[f"transformer.h.{i}.mlp.c_fc.bias"], file) for i in range(L): # (L, C, 4C) write_fun(model_tensors[f"transformer.h.{i}.mlp.c_proj.weight"], file) for i in range(L): # (L, C) write_fun(model_tensors[f"transformer.h.{i}.mlp.c_proj.bias"], file) write_fun(model_tensors["transformer.ln_f.weight"], file) # (C, ) write_fun(model_tensors["transformer.ln_f.bias"], file) # (C, ) @torch.no_grad() def pad_vocab(tensor, multiple=128, value=0): """ The dimension of the vocab size in GPT-2 is 50,257 which is unfortunately a very unfriendly number for a lot of matrix operations on the GPU. So we pad it to the nearest friendlier multiple, e.g. 50,304 if multiple=128 when we export the weights into C land. This is a NOOP algorithmically and is only done to make the tensor operations more efficient. """ assert tensor.ndim == 2 V, C = tensor.shape assert V == 50257, "just being defensive here" # calculate padded vocab size by rounding up to nearest multiple Vp = ((V + multiple - 1) // multiple) * multiple # pad the tensor pad_rows = Vp - V padded = tensor if pad_rows == 0 else F.pad(tensor, (0, 0, 0, pad_rows), value=value) assert padded.shape == (Vp, C) return padded def write_model(model, filename, dtype): # everything we need to instantiate the model # 1) header is: version int, GPTConfig ints, padding to 1024 bytes assert dtype in {"float32", "bfloat16"} # float16 todo maybe later version = { "float32": 3, # 3: all tensors are fp32, padded vocab "bfloat16": 5, # 5: all tensors are bf16, padded vocab }[dtype] header = torch.zeros(256, dtype=torch.int32) header[0] = 20240326 # magic header[1] = version # checkpoint version header[2] = model.config.block_size header[3] = model.config.vocab_size header[4] = model.config.n_layer header[5] = model.config.n_head header[6] = model.config.n_embd # 2) the parameters follow the header params = {name: param.cpu() for name, param in model.named_parameters()} # pad the vocab to a multiple of 128 here at export, for efficiency in C wte = params["transformer.wte.weight"] # (V, C) wte_padded = pad_vocab(wte) # (Vp, C) params["transformer.wte.weight"] = wte_padded # (Vp, C) print(f"padded vocab size from {wte.size(0)} to {wte_padded.size(0)}") header[7] = wte_padded.size(0) # padded vocab size store in header # now write to file with open(filename, "wb") as file: file.write(header.numpy().tobytes()) # header write_tensors(params, model.config.n_layer, file, dtype) # params print(f"wrote {filename}") def write_state(model, x, y, logits, loss, filename): # the state is used for debugging. # it contains information about the input, logits, loss, and the parameter gradients # this can be used for checking the computation correctness in C header = torch.zeros(256, dtype=torch.int32) header[0] = 20240327 # magic header[1] = 2 # run state version = 2 (1 -> 2 for padded vocab changes) header[2] = x.size(0) # batch size of the batch, B header[3] = x.size(1) # temporal extent of the batch, T grads = {name: param.grad.cpu() for name, param in model.named_parameters()} # pad the vocab grads here as well, to mirror write_model wte_grad = grads["transformer.wte.weight"] # (V, C) wte_grad_padded = pad_vocab(wte_grad, value=0) # (Vp, C) # TODO later maybe pad with nan? grads["transformer.wte.weight"] = wte_grad_padded # (Vp, C) print(f"padded vocab size in reference grads from {wte_grad.size(0)} to {wte_grad_padded.size(0)}") with open(filename, "wb") as file: # header file.write(header.numpy().tobytes()) # input x file.write(x.cpu().numpy().astype("int32").tobytes()) # (B, T) # targets y file.write(y.cpu().numpy().astype("int32").tobytes()) # (B, T) # logits (result of the model forward pass) write_fp32(logits.cpu(), file) # loss (single float, result of the cross entropy loss) write_fp32(loss.cpu(), file) # gradients write_tensors(grads, model.config.n_layer, file, "float32") print(f"wrote {filename}") def write_tokenizer(enc, filename): n = enc.max_token_value + 1 header = torch.zeros(256, dtype=torch.int32) header[0] = 20240328 # magic header[1] = 2 # tokenizer version = 2 (1 -> 2: includes EOT token) header[2] = n # number of tokens header[3] = enc.eot_token # EOT token with open(filename, "wb") as file: file.write(header.numpy().tobytes()) for i in range(n): b = enc.decode_bytes([i]) length = len(b) assert length < 256, f"Token length exceeds 255: {length}" file.write(struct.pack(""}) decode = lambda l: enc.decode(l) if master_process and args.write_tensors: # tokenizer is technically not tensors but ok write_tokenizer(enc, "gpt2_tokenizer.bin") # load the GPT-2 model weights model = GPT.from_pretrained("gpt2") model.train() model.to(device) if args.compile: if hasattr(config, "coordinate_descent_tuning"): config.coordinate_descent_tuning = True # suggested by @Chillee print0("compiling the model...") model = torch.compile(model) # ------------------------------------------------------------------------- # data loading related: long but it's just to get a single batch of data # load the tokens # note we're using val by default instead of train split just because it is smaller/faster assert os.path.isfile(args.input_bin) print0(f"loading cached tokens in {args.input_bin}") with open(args.input_bin, "rb") as f: tokens = np.frombuffer(f.read(), dtype=np.int32) # np -> tensor, long, on device tokens = torch.tensor(tokens) tokens = tokens.to(torch.long) # lightweight dataloader def get_batch(): assert B*T+1 <= len(tokens), "not enough tokens" # for 338,025 tokens. E.g. with B=8 T=1024, this will yield 41 batches before looping i = 0 while True: x = tokens[i:i+B*T].view(B, T) y = tokens[i+1:i+B*T+1].view(B, T) yield x, y i += B*T if i + B*T + 1 >= len(tokens): i = 0 # in prod we'd want to randomize the start point a bit # fetch one batch of data, which we will overfit to data_iter = iter(get_batch()) x, y = next(data_iter) # we'll overfit this batch below x = x.to(device) y = y.to(device) # ------------------------------------------------------------------------- # STAGE 1: weights / state logging for C to load later # do one forward pass to generate ground truth for our C tests if master_process and (not args.inference_only and args.write_tensors): logits, loss = model(x, y) loss.backward() # save model params, in both float32 and bfloat16 write_model(model, "gpt2_124M.bin", dtype="float32") write_model(model, "gpt2_124M_bf16.bin", dtype="bfloat16") # save x, y, logits, loss, and parameter gradients, for debugging C # always store these in fp32 to have an accurate reference (?) write_state(model, x, y, logits, loss, "gpt2_124M_debug_state.bin") # ------------------------------------------------------------------------- # STAGE 2: training loop to get timings # here we wrap model into DDP container if ddp: model = DDP(model, device_ids=[ddp_local_rank]) raw_model = model.module if ddp else model # always contains the "raw" unwrapped model # init the optimizer adam_use_fused = device == "cuda" # only works on CUDA (?) optimizer = torch.optim.Adam(model.parameters(), lr=1e-4, fused=adam_use_fused) if device == "cuda": torch.cuda.reset_peak_memory_stats() timings = [] for i in range(args.num_iterations): t0 = time.time() with ctx: logits, loss = model(x, y) del logits if not args.inference_only: optimizer.zero_grad(set_to_none=True) loss.backward() optimizer.step() # wait on the CPU for all device work to end so we get accurate per-iteration timings below if device == "mps": torch.mps.synchronize() elif device == "cuda": torch.cuda.synchronize() # time and print t1 = time.time() # the 0th iteration is often an outlier (much slower) => skip logging it tokens_per_second = ddp_world_size * B * T / (t1-t0) print0(f"iteration {i+1}, loss: {loss.item():.4f}, time: {(t1-t0)*1000:.3f}ms, tok/s: {tokens_per_second:.2f}") if i > 0 and i > args.num_iterations - 20: timings.append(t1-t0) # print the average of the last 20 timings, to get something smooth-ish timings = timings[-20:] print0(f"final {len(timings)} iters avg: {np.mean(timings)*1000:.3f}ms") print0(f"peak memory consumption: {torch.cuda.max_memory_allocated() // 1024 // 1024} MiB") # ------------------------------------------------------------------------- # STAGE 3: Few steps of inference if master_process: # before we end, let's also do one round of inference # we'll kick off the generation with "<|endoftext|>", which designates the start of a new sequence start = "<|endoftext|>" start_ids = encode(start) x = (torch.tensor(start_ids, dtype=torch.long, device=device)[None, ...]) # run generation for 16 time steps (tokens) max_new_tokens = 16 temperature = 1.0 top_k = 40 raw_model.eval() y = raw_model.generate(x, max_new_tokens, temperature=temperature, top_k=top_k) print0(decode(y[0].tolist())) print0('---------------') # ------------------------------------------------------------------------- # clean up nice if ddp: destroy_process_group()