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    20 min
    Lesson 3 of 6

    Inference Acceleration

    From the course AI Model Optimization

    Optimize inference speed with batching, caching, and specialized runtimes.

    KV Cache Optimization

    PagedAttention (vLLM)

    from vllm import LLM, SamplingParams
    
    llm = LLM(
        model="meta-llama/Llama-2-7b-hf",
        tensor_parallel_size=2,
        gpu_memory_utilization=0.9
    )
    
    # Efficient batched inference
    sampling_params = SamplingParams(temperature=0.7, max_tokens=256)
    outputs = llm.generate(prompts, sampling_params)
    

    Continuous Batching

    Traditional: Wait for batch to complete Continuous: Process requests as they finish

    Benefits:

    • 2-3x throughput improvement
    • Lower latency for short requests
    • Better GPU utilization

    Speculative Decoding

    class SpeculativeDecoder:
        def __init__(self, target_model, draft_model):
            self.target = target_model  # Large, accurate
            self.draft = draft_model    # Small, fast
    
        def generate(self, prompt, k=4):
            tokens = []
    
            while not done:
                # Draft model generates k tokens quickly
                draft_tokens = self.draft.generate(prompt, num_tokens=k)
    
                # Target model verifies in parallel
                accepted = self.target.verify(prompt, draft_tokens)
    
                tokens.extend(accepted)
                prompt = prompt + accepted
    
            return tokens
    

    Hardware-Specific Optimization

    TensorRT (NVIDIA)

    import tensorrt as trt
    
    # Convert model to TensorRT
    builder = trt.Builder(logger)
    network = builder.create_network()
    parser = trt.OnnxParser(network, logger)
    parser.parse_from_file("model.onnx")
    
    engine = builder.build_cuda_engine(network)
    # 2-4x faster inference on NVIDIA GPUs
    

    Key Takeaways

    • •PagedAttention in vLLM enables efficient memory management for long sequences
    • •Continuous batching improves throughput 2-3x over traditional batching
    • •Speculative decoding uses small draft model to accelerate large model inference
    • •TensorRT optimization provides 2-4x speedup on NVIDIA hardware
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