generate.py

# Copyright Lightning AI. Licensed under the Apache License 2.0, see LICENSE file.

import sys
import time
import warnings
from pathlib import Path
from typing import Optional

import lightning as L
import torch

# support running without installing as a package
wd = Path(__file__).parent.parent.resolve()
sys.path.append(str(wd))

from lit_llama import LLaMA, Tokenizer
from lit_llama.utils import lazy_load, llama_model_lookup, quantization


@torch.no_grad()
def generate(
    model: LLaMA,
    idx: torch.Tensor,
    max_new_tokens: int,
    *,
    max_seq_length: Optional[int] = None,
    temperature: float = 1.0,
    top_k: Optional[int] = None,
    eos_id: Optional[int] = None,
) -> torch.Tensor:
    """Takes a conditioning sequence (prompt) as input and continues to generate as many tokens as requested.

    The implementation of this function is modified from A. Karpathy's nanoGPT.

    Args:
        model: The model to use.
        idx: Tensor of shape (T) with indices of the prompt sequence.
        max_new_tokens: The number of new tokens to generate.
        max_seq_length: The maximum sequence length allowed.
        temperature: Scales the predicted logits by 1 / temperature
        top_k: If specified, only sample among the tokens with the k highest probabilities
        eos_id: If specified, stop generating any more token once the <eos> token is triggered
    """
    # create an empty tensor of the expected final shape and fill in the current tokens
    T = idx.size(0)
    T_new = T + max_new_tokens
    if max_seq_length is None:
        max_seq_length = min(T_new, model.config.block_size)

    device, dtype = idx.device, idx.dtype
    # create an empty tensor of the expected final shape and fill in the current tokens
    empty = torch.empty(T_new, dtype=dtype, device=device)
    empty[:T] = idx
    idx = empty
    input_pos = torch.arange(0, T, device=device)

    if idx.device.type == "xla":
        import torch_xla.core.xla_model as xm

        xm.mark_step()

    # generate max_new_tokens tokens
    for _ in range(max_new_tokens):
        x = idx.index_select(0, input_pos).view(1, -1)

        # forward
        logits = model(x, max_seq_length, input_pos)
        logits = logits[0, -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 = torch.where(logits < v[[-1]], -float("Inf"), logits)

        probs = torch.nn.functional.softmax(logits, dim=-1)
        idx_next = torch.multinomial(probs, num_samples=1).to(dtype=dtype)

        # advance
        input_pos = input_pos[-1:] + 1

        if idx.device.type == "xla":
            xm.mark_step()

        # concatenate the new generation
        idx = idx.index_copy(0, input_pos, idx_next)

        # if <eos> token is triggered, return the output (stop generation)
        if idx_next == eos_id:
            return idx[:input_pos]  # include the EOS token

    return idx


def main(
    prompt: str = "Hello, my name is",
    *,
    num_samples: int = 1,
    max_new_tokens: int = 50,
    top_k: int = 200,
    temperature: float = 0.8,
    checkpoint_path: Path = Path("checkpoints/lit-llama/7B/lit-llama.pth"),
    tokenizer_path: Path = Path("checkpoints/lit-llama/tokenizer.model"),
    quantize: Optional[str] = None,
) -> None:
    """Generates text samples based on a pre-trained LLaMA model and tokenizer.

    Args:
        prompt: The prompt string to use for generating the samples.
        num_samples: The number of text samples to generate.
        max_new_tokens: The number of generation steps to take.
        top_k: The number of top most probable tokens to consider in the sampling process.
        temperature: A value controlling the randomness of the sampling process. Higher values result in more random
            samples.
        checkpoint_path: The checkpoint path to load.
        tokenizer_path: The tokenizer path to load.
        quantize: Whether to quantize the model and using which method:
            ``"llm.int8"``: LLM.int8() mode,
            ``"gptq.int4"``: GPTQ 4-bit mode.
    """
    assert checkpoint_path.is_file(), checkpoint_path
    assert tokenizer_path.is_file(), tokenizer_path

    precision = "bf16-true" if torch.cuda.is_available() and torch.cuda.is_bf16_supported() else "32-true"
    fabric = L.Fabric(devices=1, precision=precision)

    print("Loading model ...", file=sys.stderr)
    t0 = time.time()
    with lazy_load(checkpoint_path) as checkpoint:
        name = llama_model_lookup(checkpoint)

        with fabric.init_module(empty_init=True), quantization(mode=quantize):
            model = LLaMA.from_name(name)

        model.load_state_dict(checkpoint)
    print(f"Time to load model: {time.time() - t0:.02f} seconds.", file=sys.stderr)

    model.eval()
    model = fabric.setup(model)

    tokenizer = Tokenizer(tokenizer_path)
    encoded = tokenizer.encode(prompt, bos=True, eos=False, device=fabric.device)
    prompt_length = encoded.size(0)

    L.seed_everything(1234)
    for i in range(num_samples):
        t0 = time.perf_counter()
        y = generate(model, encoded, max_new_tokens, temperature=temperature, top_k=top_k)
        t = time.perf_counter() - t0

        model.reset_cache()
        print(tokenizer.decode(y))
        tokens_generated = y.size(0) - prompt_length
        print(f"Time for inference {i + 1}: {t:.02f} sec total, {tokens_generated / t:.02f} tokens/sec", file=sys.stderr)
    if fabric.device.type == "cuda":
        print(f"Memory used: {torch.cuda.max_memory_reserved() / 1e9:.02f} GB", file=sys.stderr)


if __name__ == "__main__":
    from jsonargparse import CLI

    torch.set_float32_matmul_precision("high")
    warnings.filterwarnings(
        # Triggered internally at ../aten/src/ATen/EmptyTensor.cpp:31
        "ignore", 
        message="ComplexHalf support is experimental and many operators don't support it yet"
    )
    warnings.filterwarnings(
        # Triggered in bitsandbytes/autograd/_functions.py:298
        "ignore", 
        message="MatMul8bitLt: inputs will be cast from torch.bfloat16 to float16 during quantization",
    )
    CLI(main)