Solutions within vLLM community (source) to address the ever expanding problem of very high cost of GPU compute for having to recompute the previous prompts.

PagedAttention

-Core innovation in vLLM

  • Manages KV cache in blocks/pages
  • Enables efficient memory management
  • Reduces memory fragmentation
  • Allows dynamic allocation/deallocation

Continuous Batching

  • Dynamic batching of incoming requests
  • Efficient scheduling of compute resources
  • Reduces idle GPU time
  • Optimizes throughput without sacrificing latency

Block-Sparse Attention

def block_sparse_attention(query, key, value, block_size):
    # Divide attention computation into blocks
    blocks = divide_into_blocks(query, key, value, block_size)
    # Compute attention only for relevant blocks
    sparse_attention = compute_sparse_blocks(blocks)
    return sparse_attention

Cache Management Strategies

  • LRU (Least Recently Used) cache eviction
  • Priority-based cache management
  • Dynamic cache sizing
  • Intelligent prefetching

Pipeline Parallelism

  • Distributing computation across multiple GPUs
  • Efficient load balancing
  • Reduced memory pressure per device
  • Optimized inter-GPU communication

Implementation Optimizations

class KVCacheManager:
    def __init__(self, cache_size, block_size):
        self.cache = {}
        self.lru = []
        self.cache_size = cache_size
        self.block_size = block_size

    def add_to_cache(self, key, value):
        if len(self.cache) >= self.cache_size:
            # Evict least recently used
            lru_key = self.lru.pop(0)
            del self.cache[lru_key]

        self.cache[key] = value
        self.lru.append(key)

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