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前言

本项目是解读开源github的代码，该项目基于Meta最新发布的新一代开源大模型Llama-3开发，是Chinese-LLaMA-Alpaca开源大模型相关系列项目（一期、二期）的第三期。而本项目开源了中文Llama-3基座模型和中文Llama-3-Instruct指令精调大模型。这些模型在原版Llama-3的基础上使用了大规模中文数据进行增量预训练，并且使用精选指令数据进行精调，进一步提升了中文基础语义和指令理解能力，相比二代相关模型获得了显著性能提升。因此，我是基于该项目解读训练与推理相关原理与内容，并以代码形式带领读者一步一步解读，理解其大语言模型运行机理。而该博客首先给出llama3推理源码相关内容解读，我将按照源码流程给出解读。

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一、整体源码解读

1、完整main源码

我先给出完整的源码，后面推理使用哪些部分代码，我在深度解读。而一些较为简单内容我不在解读了。

if __name__ == '__main__':load_type = torch.float16# Move the model to the MPS device if availableif torch.backends.mps.is_available():device = torch.device("mps")else:if torch.cuda.is_available():device = torch.device(0)else:device = torch.device('cpu')print(f"Using device: {device}")if args.tokenizer_path is None:args.tokenizer_path = args.base_modeltokenizer = AutoTokenizer.from_pretrained(args.tokenizer_path)terminators = [tokenizer.eos_token_id,tokenizer.convert_tokens_to_ids("<|eot_id|>")]if args.use_vllm:model = LLM(model=args.base_model,tokenizer=args.tokenizer_path,tensor_parallel_size=len(args.gpus.split(',')),dtype=load_type)generation_config["stop_token_ids"] = terminatorsgeneration_config["stop"] = ["<|eot_id|>", "<|end_of_text|>"]else:if args.load_in_4bit or args.load_in_8bit:quantization_config = BitsAndBytesConfig(load_in_4bit=args.load_in_4bit,load_in_8bit=args.load_in_8bit,bnb_4bit_compute_dtype=load_type,bnb_4bit_use_double_quant=True,bnb_4bit_quant_type="nf4")model = AutoModelForCausalLM.from_pretrained(args.base_model,torch_dtype=load_type,low_cpu_mem_usage=True,device_map='auto',quantization_config=quantization_config if (args.load_in_4bit or args.load_in_8bit) else None,attn_implementation="flash_attention_2" if args.use_flash_attention_2 else "sdpa")if device==torch.device('cpu'):model.float()model.eval()# test dataif args.data_file is None:examples = sample_dataelse:with open(args.data_file, 'r') as f:examples = [line.strip() for line in f.readlines()]print("first 10 examples:")for example in examples[:10]:print(example)with torch.no_grad():if args.interactive:print("Start inference with instruction mode.")print('='*85)print("+ 该模式下仅支持单轮问答，无多轮对话能力。\n""+ 如要进行多轮对话，请使用llama.cpp")print('-'*85)print("+ This mode only supports single-turn QA.\n""+ If you want to experience multi-turn dialogue, please use llama.cpp")print('='*85)while True:raw_input_text = input("Input:")if len(raw_input_text.strip())==0:breakif args.with_prompt:input_text = generate_prompt(instruction=raw_input_text)else:input_text = raw_input_textif args.use_vllm:output = model.generate([input_text], SamplingParams(**generation_config), use_tqdm=False)response = output[0].outputs[0].textelse:inputs = tokenizer(input_text,return_tensors="pt")  #add_special_tokens=False ?generation_output = model.generate(input_ids = inputs["input_ids"].to(device),attention_mask = inputs['attention_mask'].to(device),eos_token_id=terminators,pad_token_id=tokenizer.eos_token_id,generation_config = generation_config)s = generation_output[0]output = tokenizer.decode(s, skip_special_tokens=True)if args.with_prompt:response = output.split("assistant\n\n")[-1].strip()else:response = outputprint("Response: ",response)print("\n")else:print("Start inference.")results = []if args.use_vllm:if args.with_prompt is True:inputs = [generate_prompt(example) for example in examples]else:inputs = examplesoutputs = model.generate(inputs, SamplingParams(**generation_config))for index, (example, output) in enumerate(zip(examples, outputs)):response = output.outputs[0].textprint(f"======={index}=======")print(f"Input: {example}\n")print(f"Output: {response}\n")results.append({"Input":example,"Output":response})else:for index, example in enumerate(examples):if args.with_prompt:input_text = generate_prompt(instruction=example)else:input_text = exampleinputs = tokenizer(input_text,return_tensors="pt")  #add_special_tokens=False ?generation_output = model.generate(input_ids = inputs["input_ids"].to(device),attention_mask = inputs['attention_mask'].to(device),eos_token_id=terminators,pad_token_id=tokenizer.eos_token_id,generation_config = generation_config)s = generation_output[0]output = tokenizer.decode(s,skip_special_tokens=True)if args.with_prompt:response = output.split("assistant\n\n")[1].strip()else:response = outputprint(f"======={index}=======")print(f"Input: {example}\n")print(f"Output: {response}\n")results.append({"Input":input_text,"Output":response})dirname = os.path.dirname(args.predictions_file)os.makedirs(dirname,exist_ok=True)with open(args.predictions_file,'w') as f:json.dump(results,f,ensure_ascii=False,indent=2)if args.use_vllm:with open(dirname+'/generation_config.json','w') as f:json.dump(generation_config,f,ensure_ascii=False,indent=2)else:generation_config.save_pretrained('./')

2、tokenizer加载

有关tokenzier相关加载可参考博客这里。这里，我直接给出其源码，如下：

tokenizer = AutoTokenizer.from_pretrained(args.tokenizer_path)
terminators = [tokenizer.eos_token_id,tokenizer.convert_tokens_to_ids("<|eot_id|>")]

tokenizer.eos_token_id=128009，而terminators=[128009,128009]。

3、llama3模型加载

huggingface模型加载可参考博客这里。这里，llama3的模型加载不在介绍，如下源码：

model = AutoModelForCausalLM.from_pretrained(args.base_model,  # 权重路径文件夹torch_dtype=load_type,low_cpu_mem_usage=True,device_map='auto',quantization_config=quantization_config if (args.load_in_4bit or args.load_in_8bit) else None,attn_implementation="flash_attention_2" if args.use_flash_attention_2 else "sdpa"
)
if device==torch.device('cpu'):model.float()
model.eval()

注意：model.eval()为固定权重方式，这是pytorch评估类似。

4、llama3测试数据文本加载

 # test dataif args.data_file is None:examples = sample_data  #  ["为什么要减少污染，保护环境？","你有什么建议？"]else:with open(args.data_file, 'r') as f:examples