tinygrad/examples/gpt2.py

#!/usr/bin/env python3
import argparse
from tqdm import trange
import numpy as np
from tinygrad.ops import Device
from typing import Optional
from tinygrad.tensor import Tensor
from tinygrad.nn import Embedding, Linear, LayerNorm
from tinygrad.shape.symbolic import Variable
from tinygrad.jit import TinyJit
import tiktoken
from tinygrad.nn.state import torch_load, load_state_dict
from extra.utils import fetch_as_file
from tinygrad.helpers import GlobalCounters, Timing, DEBUG, getenv

MAX_CONTEXT = 128

class Attention:
  def __init__(self, dim, n_heads):
    self.c_attn = Linear(dim, 3*dim, bias=True)
    self.c_proj = Linear(dim, dim, bias=True)
    self.n_heads = n_heads
    self.dim = dim
    self.head_dim = dim // n_heads

  def __call__(self, x:Tensor, start_pos:Variable, mask:Optional[Tensor]) -> Tensor:
    if mask is not None:
      # no symbolic shape qkv when consuming prompts
      start_pos = start_pos.val

    xqkv = self.c_attn(x)
    xq, xk, xv = [xqkv.shrink((None, None, (i*self.dim, (i+1)*self.dim))).reshape(xqkv.shape[0], xqkv.shape[1], self.n_heads, self.head_dim) for i in range(3)]
    bsz, seqlen, n_heads, head_dim = xq.shape

    # create kv cache
    if not hasattr(self, "cache_k"):
      self.cache_k, self.cache_v = Tensor.zeros(bsz, MAX_CONTEXT, self.n_heads, self.head_dim), Tensor.zeros(bsz, MAX_CONTEXT, self.n_heads, self.head_dim)

    keys = self.cache_k.shrink((None, (0, start_pos), None, None)).cat(xk, dim=1)
    values = self.cache_v.shrink((None, (0, start_pos), None, None)).cat(xv, dim=1)

    # update the cache
    self.cache_k.assign(keys.pad((None,(0,MAX_CONTEXT-start_pos-seqlen),None,None)).contiguous()).realize()
    self.cache_v.assign(values.pad((None,(0,MAX_CONTEXT-start_pos-seqlen),None,None)).contiguous()).realize()

    xq, keys, values = xq.transpose(1, 2), keys.transpose(1, 2), values.transpose(1, 2)
    return self.c_proj(xq.scaled_dot_product_attention(keys, values, mask).transpose(1, 2).reshape(bsz, seqlen, -1))

class FeedForward:
  def __init__(self, dim, hidden_dim):
    self.c_fc = Linear(dim, hidden_dim, bias=True)
    self.c_proj = Linear(hidden_dim, dim, bias=True)

  def __call__(self, x:Tensor) -> Tensor:
    return self.c_proj(self.c_fc(x).gelu())

class TransformerBlock:
  def __init__(self, dim, n_heads, norm_eps):
    self.attn = Attention(dim, n_heads)
    self.mlp = FeedForward(dim, 4*dim)
    self.ln_1 = LayerNorm(dim, norm_eps)
    self.ln_2 = LayerNorm(dim, norm_eps)

  def __call__(self, x:Tensor, start_pos:Variable, mask:Optional[Tensor]):
    h = x + self.attn(self.ln_1(x), start_pos, mask)
    return (h + self.mlp(self.ln_2(h)))

class Transformer:
  def __init__(self, dim, n_heads, n_layers, norm_eps, vocab_size, max_seq_len=1024):
    self.wte = Embedding(vocab_size, dim)
    self.wpe = Embedding(max_seq_len, dim)
    self.h = [TransformerBlock(dim, n_heads, norm_eps) for _ in range(n_layers)]
    self.ln_f = LayerNorm(dim, norm_eps)
    self.lm_head = Linear(dim, vocab_size, bias=False)
    self.forward_jit = TinyJit(self.forward)

  def forward(self, tokens:Tensor, start_pos:Variable, temperature:float=0.0):
    if not hasattr(self, 'allpos'): self.allpos = Tensor.arange(0, MAX_CONTEXT).reshape(1, -1).realize()
    _bsz, seqlen = tokens.shape

    tok_emb = self.wte(tokens)
    pos_emb = self.wpe(self.allpos.shrink((None, (start_pos, start_pos+seqlen))))
    h = tok_emb + pos_emb

    mask = Tensor.full((1, 1, seqlen, start_pos.val+seqlen), float("-inf")).triu(start_pos.val+1).realize() if seqlen > 1 else None
    for hi in self.h: h = hi(h, start_pos=start_pos, mask=mask)

    logits = self.lm_head(self.ln_f(h))
    return (logits[:, -1, :] / (temperature+1e-10)).softmax().flatten().realize()

  # TODO: fix empty token
  def __call__(self, tokens:Tensor, start_pos:Variable, temperature:float=0.0):
    return (self.forward_jit if tokens.shape[0:2] == (1,1) and getenv("JIT") else self.forward)(tokens, start_pos, temperature)

VOCAB_SIZE = 50257
MODEL_PARAMS = {
  'gpt2':         dict(n_layers=12, n_heads=12, dim=768, norm_eps=1e-5, vocab_size=VOCAB_SIZE),   # 124M params
  'gpt2-medium':  dict(n_layers=24, n_heads=16, dim=1024, norm_eps=1e-5, vocab_size=VOCAB_SIZE),  # 350M params
  'gpt2-large':   dict(n_layers=36, n_heads=20, dim=1280, norm_eps=1e-5, vocab_size=VOCAB_SIZE),  # 774M params
  'gpt2-xl':      dict(n_layers=48, n_heads=25, dim=1600, norm_eps=1e-5, vocab_size=VOCAB_SIZE),  # 1558M params
}

class GPT2:
  @staticmethod
  def build(model_size="gpt2"):
    tokenizer = tiktoken.get_encoding("gpt2")

    model = Transformer(**MODEL_PARAMS[model_size])
    weights = torch_load(fetch_as_file(f'https://huggingface.co/{model_size}/resolve/main/pytorch_model.bin'))
    # special treatment for the Conv1D weights we need to transpose
    transposed = ['attn.c_attn.weight', 'attn.c_proj.weight', 'mlp.c_fc.weight', 'mlp.c_proj.weight']
    for k in weights.keys():
      if any(k.endswith(w) for w in transposed):
        weights[k] = Tensor(weights[k].numpy().T)
    # lm head and wte are tied
    weights['lm_head.weight'] = Tensor(weights['wte.weight'].numpy())

    load_state_dict(model, weights)
    return GPT2(model, tokenizer)

  def __init__(self, model, tokenizer):
    self.model = model
    self.tokenizer = tokenizer

  def greedy_until(self, prompt:str, max_length:int, temperature:float, timing:bool=False):
    toks = self.tokenizer.encode(prompt, allowed_special={"<|endoftext|>"})
    start_pos = 0
    for _ in trange(max_length, disable=(timing==True)):
      GlobalCounters.reset()
      if timing: print("")
      st = GlobalCounters.time_sum_s
      with Timing("total ", enabled=timing):
        with Timing("ran model in ", on_exit=(lambda et: (f", {(GlobalCounters.time_sum_s-st)*1e3:.2f} ms on GPU" if DEBUG>=2 else "")+
                    f", {GlobalCounters.global_ops*1e-9:.2f} GOPS, {GlobalCounters.global_mem*1e-9:.2f} GB"+
                    (f", {GlobalCounters.global_mem*1e-9/(GlobalCounters.time_sum_s-st):.2f} GB/s" if DEBUG>=2 else "")) if DEBUG else None, enabled=timing):
          probs = self.model(Tensor([toks[start_pos:]]), Variable("start_pos", 1 if start_pos else 0, MAX_CONTEXT).bind(start_pos), temperature)
        probs_np = probs.numpy()
        tok = int(np.random.choice(len(probs_np), p=probs_np))
      start_pos = len(toks)
      toks.append(tok)
      output = self.tokenizer.decode(toks)
    return output

# **** main code ****

if __name__ == "__main__":
  Tensor.no_grad = True
  print(f"using {Device.DEFAULT} backend")

  parser = argparse.ArgumentParser(description='Run GPT2 in tinygrad', formatter_class=argparse.ArgumentDefaultsHelpFormatter)
  parser.add_argument('--prompt', type=str, default="What is the answer to life, the universe, and everything?", help="Phrase to start with")
  parser.add_argument('--count', type=int, default=100, help="Max number of tokens to generate")
  parser.add_argument('--temperature', type=float, default=0.8, help="Temperature in the softmax")
  parser.add_argument('--model_size', type=str, default="gpt2-medium", help="Size of model to use [gpt2, gpt2-medium, gpt2-large, gpt2-xl]")
  parser.add_argument('--timing', action='store_true', help="Print timing per token")
  parser.add_argument('--seed', type=int, help="Set the random seed")
  args = parser.parse_args()

  if args.seed is not None:
    Tensor._seed = args.seed
    np.random.seed(args.seed)

  print(f"using {args.model_size}")
  gpt2 = GPT2.build(args.model_size)
  print('Generating text...')
  y = gpt2.greedy_until(args.prompt, args.count, args.temperature, timing=args.timing)
  print(y)