feat: Add implementation of diff transformer

Transformers/src/diff_transformer/kernel/rotary.py

@@ -0,0 +1,334 @@
+# Copyright (c) 2023, Tri Dao.
+
+from typing import Optional, Union
+
+import torch
+
+import triton
+import triton.language as tl
+
+
+# @triton.autotune(
+#     configs=[
+#         triton.Config({"BLOCK_M": 2}),
+#         triton.Config({"BLOCK_M": 4}),
+#         triton.Config({"BLOCK_M": 8}),
+#         triton.Config({"BLOCK_M": 16}),
+#     ],
+#     key=["CACHE_KEY_SEQLEN", "BLOCK_K", "INTERLEAVED"],
+# )
+@triton.jit
+def rotary_kernel(
+    OUT,  # Pointers to matrices
+    X,
+    COS,
+    SIN,
+    CU_SEQLENS,
+    SEQLEN_OFFSETS,  # this could be int or a pointer
+    # Matrix dimensions
+    seqlen,
+    nheads,
+    rotary_dim,
+    seqlen_ro,
+    CACHE_KEY_SEQLEN,
+    # strides
+    stride_out_batch,
+    stride_out_seqlen,
+    stride_out_nheads,
+    stride_out_headdim,
+    stride_x_batch,
+    stride_x_seqlen,
+    stride_x_nheads,
+    stride_x_headdim,
+    # Meta-parameters
+    BLOCK_K: tl.constexpr,
+    IS_SEQLEN_OFFSETS_TENSOR: tl.constexpr,
+    IS_VARLEN: tl.constexpr,
+    INTERLEAVED: tl.constexpr,
+    CONJUGATE: tl.constexpr,
+    BLOCK_M: tl.constexpr,
+):
+    pid_m = tl.program_id(axis=0)
+    pid_batch = tl.program_id(axis=1)
+    pid_head = tl.program_id(axis=2)
+    rotary_dim_half = rotary_dim // 2
+
+    if not IS_VARLEN:
+        X = X + pid_batch * stride_x_batch + pid_head * stride_x_nheads
+        OUT = OUT + pid_batch * stride_out_batch + pid_head * stride_out_nheads
+    else:
+        start_idx = tl.load(CU_SEQLENS + pid_batch)
+        seqlen = tl.load(CU_SEQLENS + pid_batch + 1) - start_idx
+        X = X + start_idx * stride_x_seqlen + pid_head * stride_x_nheads
+        OUT = OUT + start_idx * stride_out_seqlen + pid_head * stride_out_nheads
+
+    if pid_m * BLOCK_M >= seqlen:
+        return
+    rm = pid_m * BLOCK_M + tl.arange(0, BLOCK_M)
+    if not IS_SEQLEN_OFFSETS_TENSOR:
+        rm_cs = rm + SEQLEN_OFFSETS
+    else:
+        rm_cs = rm + tl.load(SEQLEN_OFFSETS + pid_batch)
+    rk = tl.arange(0, BLOCK_K)
+    rk_half = tl.arange(0, BLOCK_K // 2)
+
+    if not INTERLEAVED:
+        # Load the 1st and 2nd halves of X, do calculation, then store to 1st and 2nd halves of OUT
+        X = X + (rm[:, None] * stride_x_seqlen + rk_half[None, :] * stride_x_headdim)
+        COS = COS + (rm_cs[:, None] * rotary_dim_half + rk_half[None, :])
+        SIN = SIN + (rm_cs[:, None] * rotary_dim_half + rk_half[None, :])
+        cos = tl.load(
+            COS, mask=(rm_cs[:, None] < seqlen_ro) & (rk_half[None, :] < rotary_dim_half), other=1.0
+        ).to(tl.float32)
+        sin = tl.load(
+            SIN, mask=(rm_cs[:, None] < seqlen_ro) & (rk_half[None, :] < rotary_dim_half), other=0.0
+        ).to(tl.float32)
+        x0 = tl.load(
+            X, mask=(rm[:, None] < seqlen) & (rk_half[None, :] < rotary_dim_half), other=0.0
+        ).to(tl.float32)
+        x1 = tl.load(
+            X + rotary_dim_half * stride_x_headdim,
+            mask=(rm[:, None] < seqlen) & (rk_half[None, :] < rotary_dim_half),
+            other=0.0,
+        ).to(tl.float32)
+        if CONJUGATE:
+            sin = -sin
+        o0 = x0 * cos - x1 * sin
+        o1 = x0 * sin + x1 * cos
+        # write back result
+        OUT = OUT + (rm[:, None] * stride_out_seqlen + rk_half[None, :] * stride_out_headdim)
+        tl.store(OUT, o0, mask=(rm[:, None] < seqlen) & (rk_half[None, :] < rotary_dim_half))
+        tl.store(
+            OUT + rotary_dim_half * stride_out_headdim,
+            o1,
+            mask=(rm[:, None] < seqlen) & (rk_half[None, :] < rotary_dim_half),
+        )
+    else:
+        # We don't want to load X[0, 2, 4, ...] and X[1, 3, 5, ...] separately since both are slow.
+        # Instead, we load x0 = X[0, 1, 2, 3, ...] and x1 = X[1, 0, 3, 2, ...].
+        # Loading x0 will be fast but x1 will be slow.
+        # Then we load cos = COS[0, 0, 1, 1, ...] and sin = SIN[0, 0, 1, 1, ...].
+        # Then we do the calculation and use tl.where to pick put the right outputs for the even
+        # and for the odd indices.
+        rk_swap = rk + ((rk + 1) % 2) * 2 - 1  # 1, 0, 3, 2, 5, 4, ...
+        rk_repeat = tl.arange(0, BLOCK_K) // 2
+        X0 = X + (rm[:, None] * stride_x_seqlen + rk[None, :] * stride_x_headdim)
+        X1 = X + (rm[:, None] * stride_x_seqlen + rk_swap[None, :] * stride_x_headdim)
+        COS = COS + (rm_cs[:, None] * rotary_dim_half + rk_repeat[None, :])
+        SIN = SIN + (rm_cs[:, None] * rotary_dim_half + rk_repeat[None, :])
+        cos = tl.load(
+            COS,
+            mask=(rm_cs[:, None] < seqlen_ro) & (rk_repeat[None, :] < rotary_dim_half),
+            other=1.0,
+        ).to(tl.float32)
+        sin = tl.load(
+            SIN,
+            mask=(rm_cs[:, None] < seqlen_ro) & (rk_repeat[None, :] < rotary_dim_half),
+            other=0.0,
+        ).to(tl.float32)
+        x0 = tl.load(X0, mask=(rm[:, None] < seqlen) & (rk[None, :] < rotary_dim), other=0.0).to(
+            tl.float32
+        )
+        x1 = tl.load(
+            X1, mask=(rm[:, None] < seqlen) & (rk_swap[None, :] < rotary_dim), other=0.0
+        ).to(tl.float32)
+        if CONJUGATE:
+            sin = -sin
+        x0_cos = x0 * cos
+        x1_sin = x1 * sin
+        out = tl.where(rk[None, :] % 2 == 0, x0_cos - x1_sin, x0_cos + x1_sin)
+        OUT = OUT + (rm[:, None] * stride_out_seqlen + rk[None, :] * stride_out_headdim)
+        tl.store(OUT, out, mask=(rm[:, None] < seqlen) & (rk[None, :] < rotary_dim))
+
+
+def apply_rotary(
+    x: torch.Tensor,
+    cos: torch.Tensor,
+    sin: torch.Tensor,
+    seqlen_offsets: Union[int, torch.Tensor] = 0,
+    cu_seqlens: Optional[torch.Tensor] = None,
+    max_seqlen: Optional[int] = None,
+    interleaved=False,
+    inplace=False,
+    conjugate=False,
+) -> torch.Tensor:
+    """
+    Arguments:
+        x: (batch, seqlen, nheads, headdim) if cu_seqlens is None
+            else (total_seqlen, nheads, headdim).
+        cos: (seqlen_ro, rotary_dim / 2)
+        sin: (seqlen_ro, rotary_dim / 2)
+        seqlen_offsets: integer or integer tensor of size (batch,)
+        cu_seqlens: (batch + 1,) or None
+        max_seqlen: int
+    Returns:
+        y: (batch, seqlen, nheads, headdim)
+    """
+    is_varlen = cu_seqlens is not None
+    if not is_varlen:
+        batch, seqlen, nheads, headdim = x.shape
+    else:
+        assert max_seqlen is not None, "If cu_seqlens is passed in, then max_seqlen must be passed"
+        total_seqlen, nheads, headdim = x.shape
+        batch_p_1 = cu_seqlens.shape[0]
+        batch = batch_p_1 - 1
+        seqlen = max_seqlen
+    seqlen_ro, rotary_dim = cos.shape
+    assert sin.shape == cos.shape
+    rotary_dim *= 2
+    assert rotary_dim <= headdim, "rotary_dim must be <= headdim"
+    assert headdim <= 256, "Only support headdim <= 256"
+    assert seqlen_ro >= seqlen, "seqlen_ro must be >= seqlen"
+
+    assert (
+        cos.dtype == sin.dtype
+    ), f"cos and sin must have the same dtype, got {cos.dtype} and {sin.dtype}"
+    assert (
+        x.dtype == cos.dtype
+    ), f"Input and cos/sin must have the same dtype, got {x.dtype} and {cos.dtype}"
+
+    cos, sin = cos.contiguous(), sin.contiguous()
+    if isinstance(seqlen_offsets, torch.Tensor):
+        assert seqlen_offsets.shape == (batch,)
+        assert seqlen_offsets.dtype in [torch.int32, torch.int64]
+        seqlen_offsets = seqlen_offsets.contiguous()
+    else:
+        assert seqlen_offsets + seqlen <= seqlen_ro
+
+    output = torch.empty_like(x) if not inplace else x
+    if rotary_dim < headdim and not inplace:
+        output[..., rotary_dim:].copy_(x[..., rotary_dim:])
+
+    BLOCK_K = (
+        32
+        if rotary_dim <= 32
+        else (64 if rotary_dim <= 64 else (128 if rotary_dim <= 128 else 256))
+    )
+    grid = lambda META: (triton.cdiv(seqlen, META["BLOCK_M"]), batch, nheads)  # noqa
+    BLOCK_M = 4 if interleaved else (8 if rotary_dim <= 64 else 4)
+
+    # Need this, otherwise Triton tries to launch from cuda:0 and we get
+    # ValueError: Pointer argument (at 0) cannot be accessed from Triton (cpu tensor?)
+    with torch.cuda.device(x.device.index):
+        rotary_kernel[grid](
+            output,  # data ptrs
+            x,
+            cos,
+            sin,
+            cu_seqlens,
+            seqlen_offsets,
+            seqlen,  # shapes
+            nheads,
+            rotary_dim,
+            seqlen_ro,
+            seqlen // 128,  # key for triton cache (limit number of compilations)
+            output.stride(0) if not is_varlen else 0,  # batch_strides if not varlen else 0
+            output.stride(-3),  # seqlen_stride or total_seqlen_stride
+            output.stride(-2),  # nheads_stride
+            output.stride(-1),  # headdim_stride
+            x.stride(0) if not is_varlen else 0,  # batch_strides if not varlen else 0
+            x.stride(-3),  # seqlen stride or total_seqlen_stride
+            x.stride(-2),  # nheads stride
+            x.stride(-1),  # headdim stride
+            BLOCK_K,
+            isinstance(seqlen_offsets, torch.Tensor),
+            is_varlen,
+            interleaved,
+            conjugate,
+            BLOCK_M,
+        )
+    return output
+
+
+class ApplyRotaryEmb(torch.autograd.Function):
+    @staticmethod
+    def forward(
+        ctx,
+        x,
+        cos,
+        sin,
+        interleaved=False,
+        inplace=False,
+        seqlen_offsets: Union[int, torch.Tensor] = 0,
+        cu_seqlens: Optional[torch.Tensor] = None,
+        max_seqlen: Optional[int] = None,
+    ):
+        out = apply_rotary(
+            x,
+            cos,
+            sin,
+            seqlen_offsets=seqlen_offsets,
+            cu_seqlens=cu_seqlens,
+            max_seqlen=max_seqlen,
+            interleaved=interleaved,
+            inplace=inplace,
+        )
+        if isinstance(seqlen_offsets, int):
+            # Can't save int with save_for_backward
+            ctx.save_for_backward(cos, sin, cu_seqlens)
+            ctx.seqlen_offsets = seqlen_offsets
+        else:
+            ctx.save_for_backward(cos, sin, cu_seqlens, seqlen_offsets)
+            ctx.seqlen_offsets = None
+        ctx.interleaved = interleaved
+        ctx.inplace = inplace
+        ctx.max_seqlen = max_seqlen
+        return out if not inplace else x
+
+
+    @staticmethod
+    def backward(ctx, do):
+        seqlen_offsets = ctx.seqlen_offsets
+        if seqlen_offsets is None:
+            cos, sin, cu_seqlens, seqlen_offsets = ctx.saved_tensors
+        else:
+            cos, sin, cu_seqlens = ctx.saved_tensors
+        # TD [2023-09-02]: For some reason Triton (2.0.0.post1) errors with
+        # "[CUDA]: invalid device context", and cloning makes it work. Idk why. Triton 2.1.0 works.
+        if not ctx.interleaved and not ctx.inplace:
+            do = do.clone()
+        dx = apply_rotary(
+            do,
+            cos,
+            sin,
+            seqlen_offsets=seqlen_offsets,
+            cu_seqlens=cu_seqlens,
+            max_seqlen=ctx.max_seqlen,
+            interleaved=ctx.interleaved,
+            inplace=ctx.inplace,
+            conjugate=True,
+        )
+        return dx, None, None, None, None, None, None, None
+
+
+def apply_rotary_emb(
+    x,
+    cos,
+    sin,
+    interleaved=False,
+    inplace=False,
+    seqlen_offsets: Union[int, torch.Tensor] = 0,
+    cu_seqlens: Optional[torch.Tensor] = None,
+    max_seqlen: Optional[int] = None,
+):
+    """
+    Arguments:
+        x: (batch_size, seqlen, nheads, headdim) if cu_seqlens is None
+            else (total_seqlen, nheads, headdim)
+        cos, sin: (seqlen_rotary, rotary_dim / 2)
+        interleaved: if True, rotate pairs of even and odd dimensions (GPT-J style) instead
+            of 1st half and 2nd half (GPT-NeoX style).
+        inplace: if True, apply rotary embedding in-place.
+        seqlen_offsets: (batch_size,) or int. Each sequence in x is shifted by this amount.
+            Most commonly used in inference when we have KV cache.
+        cu_seqlens: (batch + 1,) or None
+        max_seqlen: int
+    Return:
+        out: (batch_size, seqlen, nheads, headdim) if cu_seqlens is None
+            else (total_seqlen, nheads, headdim)
+    rotary_dim must be <= headdim
+    Apply rotary embedding to the first rotary_dim of x.
+    """
+    return ApplyRotaryEmb.apply(
+        x, cos, sin, interleaved, inplace, seqlen_offsets, cu_seqlens, max_seqlen
+    )