Add PyTorch-native implementation of custom layers (#1898)

tests/kernels/test_activation.py

 import pytest
 import torch
-import torch.nn.functional as F
-from transformers.activations import get_activation
 
-from vllm._C import ops
+from vllm.model_executor.layers.activation import FastGELU, NewGELU, SiluAndMul
 
 DTYPES = [torch.half, torch.bfloat16, torch.float]
 NUM_TOKENS = [7, 83, 2048]  # Arbitrary values for testing
@@ -11,11 +9,6 @@ D = [512, 4096, 5120, 13824]  # Arbitrary values for testing
 SEEDS = [0]
 
 
-def ref_silu_and_mul(x: torch.Tensor) -> torch.Tensor:
-    x1, x2 = x.chunk(chunks=2, dim=1)
-    return F.silu(x1) * x2
-
-
 @pytest.mark.parametrize("num_tokens", NUM_TOKENS)
 @pytest.mark.parametrize("d", D)
 @pytest.mark.parametrize("dtype", DTYPES)
@@ -30,9 +23,9 @@ def test_silu_and_mul(
     torch.random.manual_seed(seed)
     torch.cuda.manual_seed(seed)
     x = torch.randn(num_tokens, 2 * d, dtype=dtype, device="cuda")
-    out = torch.empty(num_tokens, d, dtype=dtype, device="cuda")
-    ops.silu_and_mul(out, x)
-    ref_out = ref_silu_and_mul(x)
+    layer = SiluAndMul()
+    out = layer(x)
+    ref_out = layer._forward(x)
     assert torch.allclose(out, ref_out, atol=1e-5, rtol=1e-5)
 
 
@@ -50,9 +43,9 @@ def test_gelu_new(
     torch.random.manual_seed(seed)
     torch.cuda.manual_seed(seed)
     x = torch.randn(num_tokens, d, dtype=dtype, device="cuda")
-    out = torch.empty(num_tokens, d, dtype=dtype, device="cuda")
-    ops.gelu_new(out, x)
-    ref_out = get_activation("gelu_new")(x)
+    layer = NewGELU()
+    out = layer(x)
+    ref_out = layer._forward(x)
     assert torch.allclose(out, ref_out, atol=1e-5, rtol=1e-5)
 
 
@@ -69,7 +62,7 @@ def test_gelu_fast(
     torch.random.manual_seed(seed)
     torch.cuda.manual_seed(seed)
     x = torch.randn(num_tokens, d, dtype=dtype, device="cuda")
-    out = torch.empty(num_tokens, d, dtype=dtype, device="cuda")
-    ops.gelu_fast(out, x)
-    ref_out = get_activation("gelu_fast")(x)
+    layer = FastGELU()
+    out = layer(x)
+    ref_out = layer._forward(x)
     assert torch.allclose(out, ref_out, atol=1e-5, rtol=1e-5)

tests/kernels/test_layernorm.py

 import pytest
 import torch
-import torch.nn as nn
 
-from vllm._C import ops
+from vllm.model_executor.layers.layernorm import RMSNorm
 
 DTYPES = [torch.half, torch.bfloat16, torch.float]
-HIDDEN_SIZES = [67, 768, 2048, 5120, 8192]  # Arbitrary values for testing
 NUM_TOKENS = [7, 83, 4096]  # Arbitrary values for testing
+HIDDEN_SIZES = [768, 5120, 8192]  # Arbitrary values for testing
+ADD_RESIDUAL = [False, True]
 SEEDS = [0]
 
 
-class RefRMSNorm(nn.Module):
-
-    def __init__(self, hidden_size, eps=1e-6):
-        super().__init__()
-        weight = torch.empty(hidden_size)
-        weight.normal_(mean=1.0, std=0.1)
-        self.weight = nn.Parameter(weight)
-        self.variance_epsilon = eps
-
-    def forward(self, hidden_states):
-        input_dtype = hidden_states.dtype
-        hidden_states = hidden_states.to(torch.float32)
-        variance = hidden_states.pow(2).mean(-1, keepdim=True)
-        hidden_states = hidden_states * torch.rsqrt(variance +
-                                                    self.variance_epsilon)
-        return self.weight * hidden_states.to(input_dtype)
-
-
 @pytest.mark.parametrize("num_tokens", NUM_TOKENS)
 @pytest.mark.parametrize("hidden_size", HIDDEN_SIZES)
+@pytest.mark.parametrize("add_residual", ADD_RESIDUAL)
 @pytest.mark.parametrize("dtype", DTYPES)
 @pytest.mark.parametrize("seed", SEEDS)
 @torch.inference_mode()
 def test_rms_norm(
     num_tokens: int,
     hidden_size: int,
+    add_residual: bool,
     dtype: torch.dtype,
     seed: int,
 ) -> None:
     torch.random.manual_seed(seed)
     torch.cuda.manual_seed(seed)
 
-    scale = float(hidden_size**-0.5)
-    x = torch.empty(num_tokens, hidden_size, dtype=dtype, device="cuda")
-    x.uniform_(-scale, scale)
-    ref = RefRMSNorm(hidden_size).to(dtype).cuda()
-
-    out = torch.empty_like(x)
-    ops.rms_norm(
-        out,
-        x,
-        ref.weight.data,
-        ref.variance_epsilon,
-    )
-    ref_out = ref(x)
-    assert torch.allclose(out, ref_out, atol=1e-2, rtol=1e-5)
+    layer = RMSNorm(hidden_size).to(dtype).cuda()
+    layer.weight.data.normal_(mean=1.0, std=0.1)
+    scale = 1 / (2 * hidden_size)
+    x = torch.randn(num_tokens, hidden_size, dtype=dtype, device="cuda")
+    x *= scale
+    residual = torch.randn_like(x) * scale if add_residual else None
+
+    # NOTE(woosuk): The reference implementation should be executed first
+    # because the custom kernel is in-place.
+    ref_out = layer._forward(x, residual)
+    out = layer(x, residual)
+    # NOTE(woosuk): LayerNorm operators (including RMS) typically have larger
+    # numerical errors than other operators because they involve reductions.
+    # Therefore, we use a larger tolerance.
+    if add_residual:
+        assert torch.allclose(out[0], ref_out[0], atol=1e-2, rtol=1e-2)
+        assert torch.allclose(out[1], ref_out[1], atol=1e-2, rtol=1e-2)
+    else:
+        assert torch.allclose(out, ref_out, atol=1e-2, rtol=1e-2)

tests/kernels/test_pos_encoding.py

-from typing import Optional, Tuple
+from typing import Optional
 
 import pytest
 import torch
-import torch.nn as nn
-import torch.nn.functional as F
 
-from vllm._C import ops
+from vllm.model_executor.layers.rotary_embedding import get_rope
 
 IS_NEOX_STYLE = [True, False]
 DTYPES = [torch.half, torch.bfloat16, torch.float]
 HEAD_SIZES = [64, 80, 96, 112, 128, 256]
 ROTARY_DIMS = [None, 32]  # None means rotary dim == head size
-NUM_HEADS = [7, 12, 40, 52]  # Arbitrary values for testing
-NUM_TOKENS = [11, 83, 2048]  # Arbitrary values for testing
+NUM_HEADS = [7, 17]  # Arbitrary values for testing
+BATCH_SIZES = [1, 5]  # Arbitrary values for testing
+SEQ_LENS = [11, 8192]  # Arbitrary values for testing
 SEEDS = [0]
 
 
-def rotate_neox(x: torch.Tensor) -> torch.Tensor:
-    x1 = x[..., :x.shape[-1] // 2]
-    x2 = x[..., x.shape[-1] // 2:]
-    return torch.cat((-x2, x1), dim=-1)
-
-
-def rotate_gptj(x: torch.Tensor) -> torch.Tensor:
-    x1 = x[..., ::2]
-    x2 = x[..., 1::2]
-    x = torch.stack((-x2, x1), dim=-1)
-    return x.flatten(-2)
-
-
-def apply_rope(
-    q: torch.Tensor,
-    k: torch.Tensor,
-    cos: torch.Tensor,
-    sin: torch.Tensor,
-    is_neox_style: bool,
-) -> Tuple[torch.Tensor, torch.Tensor]:
-    rotate_fn = rotate_neox if is_neox_style else rotate_gptj
-    q_embed = (q * cos) + (rotate_fn(q) * sin)
-    k_embed = (k * cos) + (rotate_fn(k) * sin)
-    return q_embed, k_embed
-
-
-class RefRotaryEmbedding(nn.Module):
-    """Reference implementation of rotary embedding."""
-
-    def __init__(
-        self,
-        dim: int,
-        is_neox_style: bool,
-        max_position_embeddings: int = 8192,
-        base: int = 10000,
-    ) -> None:
-        super().__init__()
-        self.rotary_dim = dim
-        self.is_neox_style = is_neox_style
-        self.max_position_embeddings = max_position_embeddings
-
-        # Create cos and sin embeddings.
-        inv_freq = 1.0 / (base**(torch.arange(0, dim, 2) / dim))
-        t = torch.arange(max_position_embeddings).float()
-        freqs = torch.einsum("i,j->ij", t, inv_freq.float())
-        if is_neox_style:
-            emb = torch.cat((freqs, freqs), dim=-1)
-        else:
-            emb = torch.repeat_interleave(freqs, 2, -1)
-        cos = emb.cos().to(dtype=inv_freq.dtype)
-        sin = emb.sin().to(dtype=inv_freq.dtype)
-        self.register_buffer("cos_cached", cos, persistent=False)
-        self.register_buffer("sin_cached", sin, persistent=False)
-
-    def forward(
-        self,
-        positions: torch.Tensor,  # [num_tokens]
-        query: torch.Tensor,  # [num_tokens, num_heads, head_size]
-        key: torch.Tensor,  # [num_tokens, num_heads, head_size]
-    ) -> Tuple[torch.Tensor, torch.Tensor]:
-        query_rot = query[..., :self.rotary_dim]
-        query_pass = query[..., self.rotary_dim:]
-        key_rot = key[..., :self.rotary_dim]
-        key_pass = key[..., self.rotary_dim:]
-
-        query_rot = query_rot.transpose(0, 1)
-        key_rot = key_rot.transpose(0, 1)
-        cos = F.embedding(positions, self.cos_cached)
-        sin = F.embedding(positions, self.sin_cached)
-
-        query_rot, key_rot = apply_rope(query_rot, key_rot, cos, sin,
-                                        self.is_neox_style)
-        query_rot = query_rot.transpose(0, 1).contiguous()
-        key_rot = key_rot.transpose(0, 1).contiguous()
-
-        query = torch.cat((query_rot, query_pass), dim=-1)
-        key = torch.cat((key_rot, key_pass), dim=-1)
-
-        # Output query/key shape: [num_tokens, num_tokens, head_size]
-        return query, key
-
-
 @pytest.mark.parametrize("is_neox_style", IS_NEOX_STYLE)
-@pytest.mark.parametrize("num_tokens", NUM_TOKENS)
+@pytest.mark.parametrize("batch_size", BATCH_SIZES)
+@pytest.mark.parametrize("seq_len", SEQ_LENS)
 @pytest.mark.parametrize("num_heads", NUM_HEADS)
 @pytest.mark.parametrize("head_size", HEAD_SIZES)
 @pytest.mark.parametrize("rotary_dim", ROTARY_DIMS)
@@ -108,7 +26,8 @@ class RefRotaryEmbedding(nn.Module):
 @torch.inference_mode()
 def test_rotary_embedding(
     is_neox_style: bool,
-    num_tokens: int,
+    batch_size: int,
+    seq_len: int,
     num_heads: int,
     head_size: int,
     rotary_dim: Optional[int],
@@ -122,53 +41,25 @@ def test_rotary_embedding(
     torch.random.manual_seed(seed)
     torch.cuda.manual_seed(seed)
 
-    positions = torch.randint(0, max_position, (num_tokens, ), device="cuda")
-    query = torch.randn(num_tokens,
+    if rotary_dim is None:
+        rotary_dim = head_size
+    rope = get_rope(head_size, rotary_dim, max_position, base, is_neox_style)
+    rope = rope.to(dtype).cuda()
+
+    positions = torch.randint(0,
+                              max_position, (batch_size, seq_len),
+                              device="cuda")
+    query = torch.randn(batch_size,
+                        seq_len,
                         num_heads * head_size,
                         dtype=dtype,
                         device="cuda")
-    key = torch.randn(num_tokens,
-                      num_heads * head_size,
-                      dtype=dtype,
-                      device="cuda")
-
-    # Create the rotary embedding.
-    inv_freq = 1.0 / (base**(
-        torch.arange(0, rotary_dim, 2, dtype=torch.float) / rotary_dim))
-    t = torch.arange(max_position).float()
-    freqs = torch.einsum("i,j -> ij", t, inv_freq)
-    cos = freqs.cos()
-    sin = freqs.sin()
-    cos_sin_cache = torch.cat((cos, sin), dim=-1)
-    cos_sin_cache = cos_sin_cache.to(dtype=dtype, device="cuda")
-
-    # Run the kernel. The kernel is in-place, so we need to clone the inputs.
-    out_query = query.clone()
-    out_key = key.clone()
-    ops.rotary_embedding(
-        positions,
-        out_query,
-        out_key,
-        head_size,
-        cos_sin_cache,
-        is_neox_style,
-    )
-
-    # Run the reference implementation.
-    ref_rotary_embedding = RefRotaryEmbedding(
-        dim=rotary_dim,
-        is_neox_style=is_neox_style,
-        max_position_embeddings=max_position,
-        base=base,
-    ).to(dtype=dtype, device="cuda")
-    ref_query, ref_key = ref_rotary_embedding(
-        positions,
-        query.view(num_tokens, num_heads, head_size),
-        key.view(num_tokens, num_heads, head_size),
-    )
-    ref_query = ref_query.view(num_tokens, num_heads * head_size)
-    ref_key = ref_key.view(num_tokens, num_heads * head_size)
+    key = torch.randn_like(query)
 
+    # NOTE(woosuk): The reference implementation should be executed first
+    # because the custom kernel is in-place.
+    ref_query, ref_key = rope._forward(positions, query, key)
+    out_query, out_key = rope.forward(positions, query, key)
     # Compare the results.
     assert torch.allclose(out_query, ref_query, atol=1e-5, rtol=1e-5)
     assert torch.allclose(out_key, ref_key, atol=1e-5, rtol=1e-5)

vllm/model_executor/layers/activation.py

 """Custom activation functions."""
+import math
 from typing import Optional
 
 import torch
 import torch.nn as nn
+import torch.nn.functional as F
 
 from vllm._C import ops
 from vllm.model_executor.layers.quantization import QuantizationConfig
@@ -22,6 +24,11 @@ class SiluAndMul(nn.Module):
         return: (batch_size, seq_len, d) or (num_tokens, d)
     """
 
+    def _forward(self, x: torch.Tensor) -> torch.Tensor:
+        """PyTorch-native implementation equivalent to forward()."""
+        d = x.shape[-1] // 2
+        return F.silu(x[..., :d]) * x[..., d:]
+
     def forward(self, x: torch.Tensor) -> torch.Tensor:
         d = x.shape[-1] // 2
         output_shape = (x.shape[:-1] + (d, ))
@@ -32,6 +39,12 @@ class SiluAndMul(nn.Module):
 
 class NewGELU(nn.Module):
 
+    def _forward(self, x: torch.Tensor) -> torch.Tensor:
+        """PyTorch-native implementation equivalent to forward()."""
+        c = math.sqrt(2.0 / math.pi)
+        return 0.5 * x * (1.0 + torch.tanh(c *
+                                           (x + 0.044715 * torch.pow(x, 3.0))))
+
     def forward(self, x: torch.Tensor) -> torch.Tensor:
         out = torch.empty_like(x)
         ops.gelu_new(out, x)
@@ -40,6 +53,11 @@ class NewGELU(nn.Module):
 
 class FastGELU(nn.Module):
 
+    def _forward(self, x: torch.Tensor) -> torch.Tensor:
+        """PyTorch-native implementation equivalent to forward()."""
+        return 0.5 * x * (1.0 + torch.tanh(x * 0.7978845608 *
+                                           (1.0 + 0.044715 * x * x)))
+
     def forward(self, x: torch.Tensor) -> torch.Tensor:
         out = torch.empty_like(x)
         ops.gelu_fast(out, x)

vllm/model_executor/layers/layernorm.py

@@ -23,6 +23,26 @@ class RMSNorm(nn.Module):
         self.weight = nn.Parameter(torch.ones(hidden_size))
         self.variance_epsilon = eps
 
+    def _forward(
+        self,
+        x: torch.Tensor,
+        residual: Optional[torch.Tensor] = None,
+    ) -> Union[torch.Tensor, Tuple[torch.Tensor, torch.Tensor]]:
+        """PyTorch-native implementation equivalent to forward()."""
+        orig_dtype = x.dtype
+        x = x.to(torch.float32)
+        if residual is not None:
+            x = x + residual.to(torch.float32)
+            residual = x.to(orig_dtype)
+
+        variance = x.pow(2).mean(dim=-1, keepdim=True)
+        x = x * torch.rsqrt(variance + self.variance_epsilon)
+        x = x.to(orig_dtype) * self.weight
+        if residual is None:
+            return x
+        else:
+            return x, residual
+
     def forward(
         self,
         x: torch.Tensor,

vllm/model_executor/layers/rotary_embedding.py

@@ -30,6 +30,19 @@ import torch.nn as nn
 from vllm._C import ops
 
 
+def _rotate_neox(x: torch.Tensor) -> torch.Tensor:
+    x1 = x[..., :x.shape[-1] // 2]
+    x2 = x[..., x.shape[-1] // 2:]
+    return torch.cat((-x2, x1), dim=-1)
+
+
+def _rotate_gptj(x: torch.Tensor) -> torch.Tensor:
+    x1 = x[..., ::2]
+    x2 = x[..., 1::2]
+    x = torch.stack((-x2, x1), dim=-1)
+    return x.flatten(-2)
+
+
 class RotaryEmbedding(nn.Module):
     """Original rotary positional embedding."""
 
@@ -81,6 +94,47 @@ class RotaryEmbedding(nn.Module):
         cache = torch.cat((cos, sin), dim=-1)
         return cache
 
+    def _forward(
+        self,
+        positions: torch.Tensor,
+        query: torch.Tensor,
+        key: torch.Tensor,
+    ) -> Tuple[torch.Tensor, torch.Tensor]:
+        """PyTorch-native implementation equivalent to forward()."""
+        query = query.view(*query.shape[:-1], -1, self.head_size)
+        key = key.view(*key.shape[:-1], -1, self.head_size)
+
+        query_rot = query[..., :self.rotary_dim]
+        key_rot = key[..., :self.rotary_dim]
+        if self.rotary_dim < self.head_size:
+            query_pass = query[..., self.rotary_dim:]
+            key_pass = key[..., self.rotary_dim:]
+
+        cos_sin = self.cos_sin_cache[positions]
+        cos, sin = cos_sin.chunk(2, dim=-1)
+        if self.is_neox_style:
+            # NOTE(woosuk): Here we assume that the positions tensor has the
+            # shape [batch_size, seq_len].
+            cos = cos.repeat(1, 1, 2).unsqueeze(-2)
+            sin = sin.repeat(1, 1, 2).unsqueeze(-2)
+        else:
+            cos = cos.repeat_interleave(2, dim=-1).unsqueeze(-2)
+            sin = sin.repeat_interleave(2, dim=-1).unsqueeze(-2)
+
+        rotate_fn = _rotate_neox if self.is_neox_style else _rotate_gptj
+        query_rot = query_rot * cos + rotate_fn(query_rot) * sin
+        key_rot = key_rot * cos + rotate_fn(key_rot) * sin
+
+        if self.rotary_dim < self.head_size:
+            query = torch.cat((query_rot, query_pass), dim=-1)
+            key = torch.cat((key_rot, key_pass), dim=-1)
+        else:
+            query = query_rot
+            key = key_rot
+        query = query.flatten(-2)
+        key = key.flatten(-2)
+        return query, key
+
     def forward(
         self,
         positions: torch.Tensor,