Fuse writing KV buffer into rope kernel (part 1: sgl-kernel) (#9077)
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fzyzcjy
@@ -2,153 +2,51 @@ from typing import Any, Dict, List, Optional, Tuple, Union
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import pytest
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import torch
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from sgl_kernel import apply_rope_with_cos_sin_cache_inplace
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# vLLM torch native
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def _apply_rotary_emb(
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x: torch.Tensor,
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cos: torch.Tensor,
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sin: torch.Tensor,
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is_neox_style: bool,
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) -> torch.Tensor:
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"""
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Args:
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x: [num_tokens, num_heads, head_size]
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cos: [num_tokens, head_size // 2]
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sin: [num_tokens, head_size // 2]
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is_neox_style: Whether to use the Neox-style or GPT-J-style rotary
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positional embeddings.
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"""
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cos = cos.unsqueeze(-2).to(x.dtype)
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sin = sin.unsqueeze(-2).to(x.dtype)
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if is_neox_style:
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x1, x2 = torch.chunk(x, 2, dim=-1)
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else:
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x1 = x[..., ::2]
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x2 = x[..., 1::2]
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o1 = x1 * cos - x2 * sin
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o2 = x2 * cos + x1 * sin
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if is_neox_style:
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return torch.cat((o1, o2), dim=-1)
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else:
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return torch.stack((o1, o2), dim=-1).flatten(-2)
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class RotaryEmbedding(torch.nn.Module):
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# Reference: https://github.com/vllm-project/vllm/blob/main/vllm/model_executor/layers/rotary_embedding.py
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def __init__(
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self,
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head_size: int,
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rotary_dim: int,
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max_position_embeddings: int,
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base: int,
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is_neox_style: bool,
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dtype: torch.dtype,
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) -> None:
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super().__init__()
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self.head_size = head_size
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self.rotary_dim = rotary_dim
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self.max_position_embeddings = max_position_embeddings
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self.base = base
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self.is_neox_style = is_neox_style
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self.dtype = dtype
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cache = self._compute_cos_sin_cache()
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self.cos_sin_cache: torch.Tensor
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self.register_buffer("cos_sin_cache", cache, persistent=False)
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def _compute_inv_freq(self, base: Union[int, float]) -> torch.Tensor:
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inv_freq = 1.0 / (
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base
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** (
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torch.arange(0, self.rotary_dim, 2, dtype=torch.float) / self.rotary_dim
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)
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)
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return inv_freq
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def _compute_cos_sin_cache(self) -> torch.Tensor:
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"""Compute the cos and sin cache."""
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inv_freq = self._compute_inv_freq(self.base)
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t = torch.arange(self.max_position_embeddings, dtype=torch.float)
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freqs = torch.einsum("i,j -> ij", t, inv_freq)
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cos = freqs.cos()
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sin = freqs.sin()
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cache = torch.cat((cos, sin), dim=-1)
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return cache
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def forward_native(
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self,
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positions: torch.Tensor,
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query: torch.Tensor,
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key: torch.Tensor,
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offsets: Optional[torch.Tensor] = None,
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) -> Tuple[torch.Tensor, torch.Tensor]:
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"""A PyTorch-native implementation of forward()."""
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if offsets is not None:
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positions = positions + offsets
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positions = positions.flatten()
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num_tokens = positions.shape[0]
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cos_sin = self.cos_sin_cache.index_select(0, positions)
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# Modification: float32 is required for the rotary embedding to work correctly
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query = query.to(torch.float32)
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key = key.to(torch.float32)
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cos, sin = cos_sin.chunk(2, dim=-1)
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query_shape = query.shape
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query = query.view(num_tokens, -1, self.head_size)
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query_rot = query[..., : self.rotary_dim]
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query_pass = query[..., self.rotary_dim :]
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query_rot = _apply_rotary_emb(query_rot, cos, sin, self.is_neox_style)
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query = torch.cat((query_rot, query_pass), dim=-1).reshape(query_shape)
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key_shape = key.shape
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key = key.view(num_tokens, -1, self.head_size)
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key_rot = key[..., : self.rotary_dim]
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key_pass = key[..., self.rotary_dim :]
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key_rot = _apply_rotary_emb(key_rot, cos, sin, self.is_neox_style)
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key = torch.cat((key_rot, key_pass), dim=-1).reshape(key_shape)
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# Modification: convert to the correct dtype
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query = query.to(self.dtype)
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key = key.to(self.dtype)
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return query, key
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class FlashInferRotaryEmbedding(RotaryEmbedding):
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def forward_cuda(
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self,
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positions: torch.Tensor,
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query: torch.Tensor,
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key: torch.Tensor,
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offsets: Optional[torch.Tensor] = None,
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) -> Tuple[torch.Tensor, torch.Tensor]:
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apply_rope_with_cos_sin_cache_inplace(
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positions=positions,
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query=query,
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key=key,
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head_size=self.head_size,
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cos_sin_cache=self.cos_sin_cache,
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is_neox=self.is_neox_style,
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)
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return query, key
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from sgl_kernel import FusedSetKVBufferArg, apply_rope_with_cos_sin_cache_inplace
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from sgl_kernel.testing.rotary_embedding import (
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FlashInferRotaryEmbedding,
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MHATokenToKVPool,
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RotaryEmbedding,
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create_inputs,
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)
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@pytest.mark.parametrize(
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"head_size, rotary_dim, max_position_embeddings, base, is_neox_style, dtype, device, batch_size, seq_len, num_q_heads, num_kv_heads",
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"head_size, rotary_dim, max_position_embeddings, base, is_neox_style, dtype, device, batch_size, seq_len, num_q_heads, num_kv_heads, save_kv_cache",
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[
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(64, 64, 32, 8000, True, torch.bfloat16, "cuda", 32, 32, 1, 1),
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(256, 128, 4096, 10000, True, torch.bfloat16, "cuda", 2, 512, 4, 2),
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(512, 128, 311, 10000, True, torch.bfloat16, "cuda", 3, 39, 4, 2),
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(128, 128, 2048, 10000, False, torch.bfloat16, "cuda", 2, 512, 32, 8),
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(128, 128, 2048, 10000, False, torch.bfloat16, "cuda", 2, 512, 16, 4),
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(512, 128, 311, 10000, False, torch.bfloat16, "cuda", 3, 39, 4, 2),
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# GPT-OSS cases
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*[
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(
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64,
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64,
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4096,
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8000,
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True,
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torch.bfloat16,
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"cuda",
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batch_size,
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seq_len,
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64,
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8,
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save_kv_cache,
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)
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for batch_size, seq_len in (
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(1, 1),
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(32, 1),
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(128, 1),
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(512, 1),
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(2, 512),
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(4, 4096),
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)
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for save_kv_cache in (False, True)
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],
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# Other cases
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(64, 64, 32, 8000, True, torch.bfloat16, "cuda", 32, 32, 1, 1, False),
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(256, 128, 4096, 10000, True, torch.bfloat16, "cuda", 2, 512, 4, 2, False),
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(512, 128, 311, 10000, True, torch.bfloat16, "cuda", 3, 39, 4, 2, False),
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(128, 128, 2048, 10000, False, torch.bfloat16, "cuda", 2, 512, 32, 8, False),
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(128, 128, 2048, 10000, False, torch.bfloat16, "cuda", 2, 512, 16, 4, False),
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(512, 128, 311, 10000, False, torch.bfloat16, "cuda", 3, 39, 4, 2, False),
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],
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)
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def test_correctness(
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@@ -163,34 +61,77 @@ def test_correctness(
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seq_len: int,
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num_q_heads: int,
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num_kv_heads: int,
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save_kv_cache: bool,
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):
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rope_ref = RotaryEmbedding(
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head_size, rotary_dim, max_position_embeddings, base, is_neox_style, dtype
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).to(device)
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rope_flashinfer = FlashInferRotaryEmbedding(
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head_size, rotary_dim, max_position_embeddings, base, is_neox_style, dtype
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).to(device)
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pos_ids = torch.arange(seq_len, device=device).repeat(batch_size)
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query = torch.randn(
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batch_size * seq_len, num_q_heads * head_size, dtype=dtype, device=device
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)
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key = torch.randn(
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batch_size * seq_len, num_kv_heads * head_size, dtype=dtype, device=device
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config = dict(
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head_size=head_size,
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rotary_dim=rotary_dim,
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max_position_embeddings=max_position_embeddings,
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base=base,
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is_neox_style=is_neox_style,
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dtype=dtype,
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)
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query_ref, key_ref = query.clone(), key.clone()
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query_flashinfer, key_flashinfer = query.clone(), key.clone()
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rope_ref = RotaryEmbedding(**config).to(device)
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rope_flashinfer = FlashInferRotaryEmbedding(**config).to(device)
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inputs = create_inputs(
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head_size=head_size,
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batch_size=batch_size,
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seq_len=seq_len,
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device=device,
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dtype=dtype,
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num_q_heads=num_q_heads,
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num_kv_heads=num_kv_heads,
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)
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if save_kv_cache:
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pool_ref = MHATokenToKVPool(head_num=num_kv_heads, head_dim=head_size)
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pool_flashinfer = MHATokenToKVPool(head_num=num_kv_heads, head_dim=head_size)
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query_ref, key_ref = inputs["query"].clone(), inputs["key"].clone()
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query_flashinfer, key_flashinfer = inputs["query"].clone(), inputs["key"].clone()
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query_ref_out, key_ref_out = rope_ref.forward_native(
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inputs["pos_ids"], query_ref, key_ref
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)
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if save_kv_cache:
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pool_ref.set_kv_buffer(
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loc=inputs["out_cache_loc"],
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cache_k=key_ref_out.view(-1, num_kv_heads, head_size),
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cache_v=inputs["value"].view(-1, num_kv_heads, head_size),
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)
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query_ref_out, key_ref_out = rope_ref.forward_native(pos_ids, query_ref, key_ref)
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query_flashinfer_out, key_flashinfer_out = rope_flashinfer.forward_cuda(
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pos_ids, query_flashinfer, key_flashinfer
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inputs["pos_ids"],
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query_flashinfer,
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key_flashinfer,
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fused_set_kv_buffer_arg=(
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FusedSetKVBufferArg(
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value=inputs["value"],
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k_buffer=pool_flashinfer.k_buffer[0].view(-1, num_kv_heads * head_size),
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v_buffer=pool_flashinfer.v_buffer[0].view(-1, num_kv_heads * head_size),
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k_scale=None,
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v_scale=None,
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cache_loc=inputs["out_cache_loc"],
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)
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if save_kv_cache
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else None
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),
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)
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torch.testing.assert_close(
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query_ref_out, query_flashinfer_out, atol=1e-2, rtol=1e-2
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)
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torch.testing.assert_close(key_ref_out, key_flashinfer_out, atol=1e-2, rtol=1e-2)
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if save_kv_cache:
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for field in ["k_buffer", "v_buffer"]:
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x_ref = getattr(pool_ref, field)[0]
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x_flashinfer = getattr(pool_flashinfer, field)[0]
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torch.testing.assert_close(x_ref, x_flashinfer, atol=1e-2, rtol=1e-2)
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nonzero_ref = x_ref != 0
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nonzero_flashinfer = x_ref != 0
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assert torch.all(nonzero_ref == nonzero_flashinfer)
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if __name__ == "__main__":
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