94 lines
2.7 KiB
Python
94 lines
2.7 KiB
Python
"""
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Hybrid sparse attention policy.
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Allows using different policies for prefill vs decode phases.
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This is useful because optimal sparsity patterns often differ:
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- Prefill: fixed patterns work well (e.g., VerticalSlash)
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- Decode: query-aware selection helps (e.g., Quest)
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"""
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from typing import List
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import torch
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from .policy import SparsePolicy, PolicyContext
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class HybridPolicy(SparsePolicy):
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"""
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Hybrid policy that uses different policies for prefill and decode.
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Example usage:
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```python
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from nanovllm.kvcache.sparse import (
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HybridPolicy, VerticalSlashPolicy, QuestPolicy,
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VerticalSlashConfig, QuestConfig, BlockMetadataManager
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)
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# Prefill: use fast fixed pattern
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prefill_policy = VerticalSlashPolicy(VerticalSlashConfig(
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num_sink_blocks=1,
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local_window_blocks=3,
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))
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# Decode: use query-aware selection
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metadata = BlockMetadataManager(num_blocks, num_layers, num_heads, head_dim)
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decode_policy = QuestPolicy(QuestConfig(topk_blocks=8), metadata)
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# Combine
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policy = HybridPolicy(prefill_policy, decode_policy)
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```
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"""
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def __init__(
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self,
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prefill_policy: SparsePolicy,
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decode_policy: SparsePolicy,
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):
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"""
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Initialize hybrid policy.
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Args:
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prefill_policy: Policy to use during prefill phase
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decode_policy: Policy to use during decode phase
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"""
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self.prefill_policy = prefill_policy
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self.decode_policy = decode_policy
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def select_blocks(
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self,
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available_blocks: List[int],
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ctx: PolicyContext,
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) -> List[int]:
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"""Delegate to appropriate policy based on phase."""
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if ctx.is_prefill:
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return self.prefill_policy.select_blocks(available_blocks, ctx)
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else:
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return self.decode_policy.select_blocks(available_blocks, ctx)
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def on_block_offloaded(
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self,
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cpu_block_id: int,
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layer_id: int,
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k_cache: torch.Tensor,
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num_valid_tokens: int,
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) -> None:
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"""Forward to both policies (both may need metadata updates)."""
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self.prefill_policy.on_block_offloaded(
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cpu_block_id, layer_id, k_cache, num_valid_tokens
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)
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self.decode_policy.on_block_offloaded(
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cpu_block_id, layer_id, k_cache, num_valid_tokens
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)
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def reset(self) -> None:
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"""Reset both policies."""
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self.prefill_policy.reset()
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self.decode_policy.reset()
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def __repr__(self) -> str:
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return (
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f"HybridPolicy(\n"
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f" prefill={self.prefill_policy},\n"
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f" decode={self.decode_policy}\n"
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f")"
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)
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