Initial commit for testing triton flash attention

triton.py

@@ -0,0 +1,26 @@
+import torch
+from triton_flash_atn import _attention
+
+# Define dimensions
+batch_size = 2
+num_heads = 4
+seq_len = 128
+head_dim = 64
+
+# Create random input tensors for Q, K, V
+q = torch.randn(batch_size, num_heads, seq_len, head_dim,
+                dtype=torch.float16, device='cuda')
+k = torch.randn(batch_size, num_heads, seq_len, head_dim,
+                dtype=torch.float16, device='cuda')
+v = torch.randn(batch_size, num_heads, seq_len, head_dim,
+                dtype=torch.float16, device='cuda')
+
+# Define whether the attention is causal and the scaling factor
+causal = False
+sm_scale = 1.0 / (head_dim ** 0.5)
+
+# Apply flash attention
+attention = _attention.apply
+output = attention(q, k, v, causal, sm_scale)
+
+print(output)

triton_flash_atn.py

@@ -0,0 +1,527 @@
+"""
+Fused Attention
+===============
+
+This is a Triton implementation of the Flash Attention v2 algorithm from Tri Dao (https://tridao.me/publications/flash2/flash2.pdf)
+Credits: OpenAI kernel team
+
+Extra Credits:
+- Original flash attention paper (https://arxiv.org/abs/2205.14135)
+- Rabe and Staats (https://arxiv.org/pdf/2112.05682v2.pdf)
+
+"""
+
+import torch
+
+import triton
+import triton.language as tl
+
+
+def is_hip():
+    return triton.runtime.driver.HIP
+
+
+@triton.jit
+def _attn_fwd_inner(acc, l_i, m_i, q,  #
+                    K_block_ptr, V_block_ptr,  #
+                    start_m, qk_scale,  #
+                    BLOCK_M: tl.constexpr, HEAD_DIM: tl.constexpr, BLOCK_N: tl.constexpr,  #
+                    STAGE: tl.constexpr, offs_m: tl.constexpr, offs_n: tl.constexpr,  #
+                    N_CTX: tl.constexpr, fp8_v: tl.constexpr):
+    # range of values handled by this stage
+    if STAGE == 1:
+        lo, hi = 0, start_m * BLOCK_M
+    elif STAGE == 2:
+        lo, hi = start_m * BLOCK_M, (start_m + 1) * BLOCK_M
+        lo = tl.multiple_of(lo, BLOCK_M)
+    # causal = False
+    else:
+        lo, hi = 0, N_CTX
+    K_block_ptr = tl.advance(K_block_ptr, (0, lo))
+    V_block_ptr = tl.advance(V_block_ptr, (lo, 0))
+    # loop over k, v and update accumulator
+    for start_n in range(lo, hi, BLOCK_N):
+        start_n = tl.multiple_of(start_n, BLOCK_N)
+        # -- compute qk ----
+        k = tl.load(K_block_ptr)
+        qk = tl.dot(q, k)
+        if STAGE == 2:
+            mask = offs_m[:, None] >= (start_n + offs_n[None, :])
+            qk = qk * qk_scale + tl.where(mask, 0, -1.0e6)
+            m_ij = tl.maximum(m_i, tl.max(qk, 1))
+            qk -= m_ij[:, None]
+        else:
+            m_ij = tl.maximum(m_i, tl.max(qk, 1) * qk_scale)
+            qk = qk * qk_scale - m_ij[:, None]
+        p = tl.math.exp2(qk)
+        l_ij = tl.sum(p, 1)
+        # -- update m_i and l_i
+        alpha = tl.math.exp2(m_i - m_ij)
+        l_i = l_i * alpha + l_ij
+        # -- update output accumulator --
+        acc = acc * alpha[:, None]
+        # update acc
+        v = tl.load(V_block_ptr)
+        if fp8_v:
+            p = p.to(tl.float8e5)
+        else:
+            p = p.to(tl.float16)
+        acc = tl.dot(p, v, acc)
+        # update m_i and l_i
+        m_i = m_ij
+        V_block_ptr = tl.advance(V_block_ptr, (BLOCK_N, 0))
+        K_block_ptr = tl.advance(K_block_ptr, (0, BLOCK_N))
+    return acc, l_i, m_i
+
+
+# We don't run auto-tuning every time to keep the tutorial fast. Keeping
+# the code below and commenting out the equivalent parameters is convenient for
+# re-tuning.
+configs = [
+    triton.Config({'BLOCK_M': BM, 'BLOCK_N': BN}, num_stages=s, num_warps=w)
+    for BM in [64, 128]
+    for BN in [32, 64]
+    for s in ([1] if is_hip() else [3, 4, 7])
+    for w in [4, 8]
+]
+
+
+def keep(conf):
+    BLOCK_M = conf.kwargs["BLOCK_M"]
+    BLOCK_N = conf.kwargs["BLOCK_N"]
+    if BLOCK_M * BLOCK_N < 128 * 128 and conf.num_warps == 8:
+        return False
+    return True
+
+
+@triton.autotune(list(filter(keep, configs)), key=["N_CTX"])
+@triton.jit
+def _attn_fwd(Q, K, V, sm_scale, M, Out,  #
+              stride_qz, stride_qh, stride_qm, stride_qk,  #
+              stride_kz, stride_kh, stride_kn, stride_kk,  #
+              stride_vz, stride_vh, stride_vk, stride_vn,  #
+              stride_oz, stride_oh, stride_om, stride_on,  #
+              Z, H, N_CTX,  #
+              BLOCK_M: tl.constexpr,  #
+              BLOCK_N: tl.constexpr,  #
+              HEAD_DIM: tl.constexpr,  #
+              STAGE: tl.constexpr  #
+              ):
+    tl.static_assert(BLOCK_N <= HEAD_DIM)
+    start_m = tl.program_id(0)
+    off_hz = tl.program_id(1)
+    off_z = off_hz // H
+    off_h = off_hz % H
+    qvk_offset = off_z.to(tl.int64) * stride_qz + \
+        off_h.to(tl.int64) * stride_qh
+
+    # block pointers
+    Q_block_ptr = tl.make_block_ptr(
+        base=Q + qvk_offset,
+        shape=(N_CTX, HEAD_DIM),
+        strides=(stride_qm, stride_qk),
+        offsets=(start_m * BLOCK_M, 0),
+        block_shape=(BLOCK_M, HEAD_DIM),
+        order=(1, 0),
+    )
+    v_order: tl.constexpr = (
+        0, 1) if V.dtype.element_ty == tl.float8e5 else (1, 0)
+    V_block_ptr = tl.make_block_ptr(
+        base=V + qvk_offset,
+        shape=(N_CTX, HEAD_DIM),
+        strides=(stride_vk, stride_vn),
+        offsets=(0, 0),
+        block_shape=(BLOCK_N, HEAD_DIM),
+        order=v_order,
+    )
+    K_block_ptr = tl.make_block_ptr(
+        base=K + qvk_offset,
+        shape=(HEAD_DIM, N_CTX),
+        strides=(stride_kk, stride_kn),
+        offsets=(0, 0),
+        block_shape=(HEAD_DIM, BLOCK_N),
+        order=(0, 1),
+    )
+    O_block_ptr = tl.make_block_ptr(
+        base=Out + qvk_offset,
+        shape=(N_CTX, HEAD_DIM),
+        strides=(stride_om, stride_on),
+        offsets=(start_m * BLOCK_M, 0),
+        block_shape=(BLOCK_M, HEAD_DIM),
+        order=(1, 0),
+    )
+    # initialize offsets
+    offs_m = start_m * BLOCK_M + tl.arange(0, BLOCK_M)
+    offs_n = tl.arange(0, BLOCK_N)
+    # initialize pointer to m and l
+    m_i = tl.zeros([BLOCK_M], dtype=tl.float32) - float("inf")
+    l_i = tl.zeros([BLOCK_M], dtype=tl.float32) + 1.0
+    acc = tl.zeros([BLOCK_M, HEAD_DIM], dtype=tl.float32)
+    # load scales
+    qk_scale = sm_scale
+    qk_scale *= 1.44269504  # 1/log(2)
+    # load q: it will stay in SRAM throughout
+    q = tl.load(Q_block_ptr)
+    # stage 1: off-band
+    # For causal = True, STAGE = 3 and _attn_fwd_inner gets 1 as its STAGE
+    # For causal = False, STAGE = 1, and _attn_fwd_inner gets 3 as its STAGE
+    if STAGE & 1:
+        acc, l_i, m_i = _attn_fwd_inner(acc, l_i, m_i, q, K_block_ptr, V_block_ptr,  #
+                                        start_m, qk_scale,  #
+                                        BLOCK_M, HEAD_DIM, BLOCK_N,  #
+                                        4 - STAGE, offs_m, offs_n, N_CTX, V.dtype.element_ty == tl.float8e5  #
+                                        )
+    # stage 2: on-band
+    if STAGE & 2:
+        # barrier makes it easier for compielr to schedule the
+        # two loops independently
+        acc, l_i, m_i = _attn_fwd_inner(acc, l_i, m_i, q, K_block_ptr, V_block_ptr,  #
+                                        start_m, qk_scale,  #
+                                        BLOCK_M, HEAD_DIM, BLOCK_N,  #
+                                        2, offs_m, offs_n, N_CTX, V.dtype.element_ty == tl.float8e5  #
+                                        )
+    # epilogue
+    m_i += tl.math.log2(l_i)
+    acc = acc / l_i[:, None]
+    m_ptrs = M + off_hz * N_CTX + offs_m
+    tl.store(m_ptrs, m_i)
+    tl.store(O_block_ptr, acc.to(Out.type.element_ty))
+
+
+@triton.jit
+def _attn_bwd_preprocess(O, DO,  #
+                         Delta,  #
+                         Z, H, N_CTX,  #
+                         BLOCK_M: tl.constexpr, HEAD_DIM: tl.constexpr  #
+                         ):
+    off_m = tl.program_id(0) * BLOCK_M + tl.arange(0, BLOCK_M)
+    off_hz = tl.program_id(1)
+    off_n = tl.arange(0, HEAD_DIM)
+    # load
+    o = tl.load(O + off_hz * HEAD_DIM * N_CTX +
+                off_m[:, None] * HEAD_DIM + off_n[None, :])
+    do = tl.load(DO + off_hz * HEAD_DIM * N_CTX +
+                 off_m[:, None] * HEAD_DIM + off_n[None, :]).to(tl.float32)
+    delta = tl.sum(o * do, axis=1)
+    # write-back
+    tl.store(Delta + off_hz * N_CTX + off_m, delta)
+
+
+# The main inner-loop logic for computing dK and dV.
+@triton.jit
+def _attn_bwd_dkdv(dk, dv,  #
+                   Q, k, v, sm_scale,  #
+                   DO,  #
+                   M, D,  #
+                   # shared by Q/K/V/DO.
+                   stride_tok, stride_d,  #
+                   H, N_CTX, BLOCK_M1: tl.constexpr,  #
+                   BLOCK_N1: tl.constexpr,  #
+                   HEAD_DIM: tl.constexpr,  #
+                   # Filled in by the wrapper.
+                   start_n, start_m, num_steps,  #
+                   MASK: tl.constexpr):
+    offs_m = start_m + tl.arange(0, BLOCK_M1)
+    offs_n = start_n + tl.arange(0, BLOCK_N1)
+    offs_k = tl.arange(0, HEAD_DIM)
+    qT_ptrs = Q + offs_m[None, :] * stride_tok + offs_k[:, None] * stride_d
+    do_ptrs = DO + offs_m[:, None] * stride_tok + offs_k[None, :] * stride_d
+    # BLOCK_N1 must be a multiple of BLOCK_M1, otherwise the code wouldn't work.
+    tl.static_assert(BLOCK_N1 % BLOCK_M1 == 0)
+    curr_m = start_m
+    step_m = BLOCK_M1
+    for blk_idx in range(num_steps):
+        qT = tl.load(qT_ptrs)
+        # Load m before computing qk to reduce pipeline stall.
+        offs_m = curr_m + tl.arange(0, BLOCK_M1)
+        m = tl.load(M + offs_m)
+        qkT = tl.dot(k, qT)
+        pT = tl.math.exp2(qkT - m[None, :])
+        # Autoregressive masking.
+        if MASK:
+            mask = (offs_m[None, :] >= offs_n[:, None])
+            pT = tl.where(mask, pT, 0.0)
+        do = tl.load(do_ptrs)
+        # Compute dV.
+        ppT = pT
+        ppT = ppT.to(tl.float16)
+        dv += tl.dot(ppT, do)
+        # D (= delta) is pre-divided by ds_scale.
+        Di = tl.load(D + offs_m)
+        # Compute dP and dS.
+        dpT = tl.dot(v, tl.trans(do)).to(tl.float32)
+        dsT = pT * (dpT - Di[None, :])
+        dsT = dsT.to(tl.float16)
+        dk += tl.dot(dsT, tl.trans(qT))
+        # Increment pointers.
+        curr_m += step_m
+        qT_ptrs += step_m * stride_tok
+        do_ptrs += step_m * stride_tok
+    return dk, dv
+
+
+# the main inner-loop logic for computing dQ
+@triton.jit
+def _attn_bwd_dq(dq, q, K, V,  #
+                 do, m, D,
+                 # shared by Q/K/V/DO.
+                 stride_tok, stride_d,  #
+                 H, N_CTX,  #
+                 BLOCK_M2: tl.constexpr,  #
+                 BLOCK_N2: tl.constexpr,  #
+                 HEAD_DIM: tl.constexpr,
+                 # Filled in by the wrapper.
+                 start_m, start_n, num_steps,  #
+                 MASK: tl.constexpr):
+    offs_m = start_m + tl.arange(0, BLOCK_M2)
+    offs_n = start_n + tl.arange(0, BLOCK_N2)
+    offs_k = tl.arange(0, HEAD_DIM)
+    kT_ptrs = K + offs_n[None, :] * stride_tok + offs_k[:, None] * stride_d
+    vT_ptrs = V + offs_n[None, :] * stride_tok + offs_k[:, None] * stride_d
+    # D (= delta) is pre-divided by ds_scale.
+    Di = tl.load(D + offs_m)
+    # BLOCK_M2 must be a multiple of BLOCK_N2, otherwise the code wouldn't work.
+    tl.static_assert(BLOCK_M2 % BLOCK_N2 == 0)
+    curr_n = start_n
+    step_n = BLOCK_N2
+    for blk_idx in range(num_steps):
+        kT = tl.load(kT_ptrs)
+        vT = tl.load(vT_ptrs)
+        qk = tl.dot(q, kT)
+        p = tl.math.exp2(qk - m)
+        # Autoregressive masking.
+        if MASK:
+            offs_n = curr_n + tl.arange(0, BLOCK_N2)
+            mask = (offs_m[:, None] >= offs_n[None, :])
+            p = tl.where(mask, p, 0.0)
+        # Compute dP and dS.
+        dp = tl.dot(do, vT).to(tl.float32)
+        ds = p * (dp - Di[:, None])
+        ds = ds.to(tl.float16)
+        # Compute dQ.
+        # NOTE: We need to de-scale dq in the end, because kT was pre-scaled.
+        dq += tl.dot(ds, tl.trans(kT))
+        # Increment pointers.
+        curr_n += step_n
+        kT_ptrs += step_n * stride_tok
+        vT_ptrs += step_n * stride_tok
+    return dq
+
+
+@triton.jit
+def _attn_bwd(Q, K, V, sm_scale,  #
+              DO,  #
+              DQ, DK, DV,  #
+              M, D,
+              # shared by Q/K/V/DO.
+              stride_z, stride_h, stride_tok, stride_d,  #
+              H, N_CTX,  #
+              BLOCK_M1: tl.constexpr,  #
+              BLOCK_N1: tl.constexpr,  #
+              BLOCK_M2: tl.constexpr,  #
+              BLOCK_N2: tl.constexpr,  #
+              BLK_SLICE_FACTOR: tl.constexpr,  #
+              HEAD_DIM: tl.constexpr):
+    LN2: tl.constexpr = 0.6931471824645996  # = ln(2)
+
+    bhid = tl.program_id(2)
+    off_chz = (bhid * N_CTX).to(tl.int64)
+    adj = (stride_h * (bhid % H) + stride_z * (bhid // H)).to(tl.int64)
+    pid = tl.program_id(0)
+
+    # offset pointers for batch/head
+    Q += adj
+    K += adj
+    V += adj
+    DO += adj
+    DQ += adj
+    DK += adj
+    DV += adj
+    M += off_chz
+    D += off_chz
+
+    # load scales
+    offs_k = tl.arange(0, HEAD_DIM)
+
+    start_n = pid * BLOCK_N1
+    start_m = start_n
+
+    MASK_BLOCK_M1: tl.constexpr = BLOCK_M1 // BLK_SLICE_FACTOR
+    offs_n = start_n + tl.arange(0, BLOCK_N1)
+
+    dv = tl.zeros([BLOCK_N1, HEAD_DIM], dtype=tl.float32)
+    dk = tl.zeros([BLOCK_N1, HEAD_DIM], dtype=tl.float32)
+
+    # load K and V: they stay in SRAM throughout the inner loop.
+    k = tl.load(K + offs_n[:, None] * stride_tok + offs_k[None, :] * stride_d)
+    v = tl.load(V + offs_n[:, None] * stride_tok + offs_k[None, :] * stride_d)
+
+    num_steps = BLOCK_N1 // MASK_BLOCK_M1
+
+    dk, dv = _attn_bwd_dkdv(dk, dv,  #
+                            Q, k, v, sm_scale,  #
+                            DO,  #
+                            M, D,  #
+                            stride_tok, stride_d,  #
+                            H, N_CTX,  #
+                            MASK_BLOCK_M1, BLOCK_N1, HEAD_DIM,  #
+                            start_n, start_m, num_steps,  #
+                            MASK=True  #
+                            )
+
+    start_m += num_steps * MASK_BLOCK_M1
+    num_steps = (N_CTX - start_m) // BLOCK_M1
+
+    # Compute dK and dV for non-masked blocks.
+    dk, dv = _attn_bwd_dkdv(  #
+        dk, dv,  #
+        Q, k, v, sm_scale,  #
+        DO,  #
+        M, D,  #
+        stride_tok, stride_d,  #
+        H, N_CTX,  #
+        BLOCK_M1, BLOCK_N1, HEAD_DIM,  #
+        start_n, start_m, num_steps,  #
+        MASK=False  #
+    )
+
+    dv_ptrs = DV + offs_n[:, None] * stride_tok + offs_k[None, :] * stride_d
+    tl.store(dv_ptrs, dv)
+
+    # Write back dK.
+    dk *= sm_scale
+    dk_ptrs = DK + offs_n[:, None] * stride_tok + offs_k[None, :] * stride_d
+    tl.store(dk_ptrs, dk)
+
+    # THIS BLOCK DOES DQ:
+    start_m = pid * BLOCK_M2
+    end_n = start_m + BLOCK_M2
+
+    MASK_BLOCK_N2: tl.constexpr = BLOCK_N2 // BLK_SLICE_FACTOR
+    offs_m = start_m + tl.arange(0, BLOCK_M2)
+
+    q = tl.load(Q + offs_m[:, None] * stride_tok + offs_k[None, :] * stride_d)
+    dq = tl.zeros([BLOCK_M2, HEAD_DIM], dtype=tl.float32)
+    do = tl.load(DO + offs_m[:, None] * stride_tok +
+                 offs_k[None, :] * stride_d)
+
+    m = tl.load(M + offs_m)
+    m = m[:, None]
+
+    # Compute dQ for masked (diagonal) blocks.
+    # NOTE: This code scans each row of QK^T backward (from right to left,
+    # but inside each call to _attn_bwd_dq, from left to right), but that's
+    # not due to anything important.  I just wanted to reuse the loop
+    # structure for dK & dV above as much as possible.
+    num_steps = BLOCK_M2 // MASK_BLOCK_N2
+    dq = _attn_bwd_dq(dq, q, K, V,  #
+                      do, m, D,  #
+                      stride_tok, stride_d,  #
+                      H, N_CTX,  #
+                      BLOCK_M2, MASK_BLOCK_N2, HEAD_DIM,  #
+                      start_m, end_n - num_steps * MASK_BLOCK_N2, num_steps,  #
+                      MASK=True  #
+                      )
+    end_n -= num_steps * MASK_BLOCK_N2
+    # stage 2
+    num_steps = end_n // BLOCK_N2
+    dq = _attn_bwd_dq(dq, q, K, V,  #
+                      do, m, D,  #
+                      stride_tok, stride_d,  #
+                      H, N_CTX,  #
+                      BLOCK_M2, BLOCK_N2, HEAD_DIM,  #
+                      start_m, end_n - num_steps * BLOCK_N2, num_steps,  #
+                      MASK=False  #
+                      )
+    # Write back dQ.
+    dq_ptrs = DQ + offs_m[:, None] * stride_tok + offs_k[None, :] * stride_d
+    dq *= LN2
+    tl.store(dq_ptrs, dq)
+
+
+class _attention(torch.autograd.Function):
+
+    @staticmethod
+    def forward(ctx, q, k, v, causal, sm_scale):
+        # shape constraints
+        HEAD_DIM_Q, HEAD_DIM_K = q.shape[-1], k.shape[-1]
+        # when v is in float8_e5m2 it is transposed.
+        HEAD_DIM_V = v.shape[-2] if v.dtype == torch.float8_e5m2 else v.shape[-1]
+        assert HEAD_DIM_Q == HEAD_DIM_K and HEAD_DIM_K == HEAD_DIM_V
+        assert HEAD_DIM_K in {16, 32, 64, 128, 256}
+        o = torch.empty_like(q)
+        stage = 3 if causal else 1
+        extra_kern_args = {}
+        # Tuning for AMD target
+        if is_hip():
+            waves_per_eu = 3 if HEAD_DIM_K <= 64 else 2
+            extra_kern_args = {"waves_per_eu": waves_per_eu,
+                               "allow_flush_denorm": True}
+
+        def grid(args): return (triton.cdiv(
+            q.shape[2], args["BLOCK_M"]), q.shape[0] * q.shape[1], 1)
+        M = torch.empty((q.shape[0], q.shape[1], q.shape[2]),
+                        device=q.device, dtype=torch.float32)
+        _attn_fwd[grid](
+            q, k, v, sm_scale, M, o,  #
+            q.stride(0), q.stride(1), q.stride(2), q.stride(3),  #
+            k.stride(0), k.stride(1), k.stride(2), k.stride(3),  #
+            v.stride(0), v.stride(1), v.stride(2), v.stride(3),  #
+            o.stride(0), o.stride(1), o.stride(2), o.stride(3),  #
+            q.shape[0], q.shape[1],  #
+            N_CTX=q.shape[2],  #
+            HEAD_DIM=HEAD_DIM_K,  #
+            STAGE=stage,  #
+            **extra_kern_args)
+
+        ctx.save_for_backward(q, k, v, o, M)
+        ctx.grid = grid
+        ctx.sm_scale = sm_scale
+        ctx.HEAD_DIM = HEAD_DIM_K
+        ctx.causal = causal
+        return o
+
+    @staticmethod
+    def backward(ctx, do):
+        q, k, v, o, M = ctx.saved_tensors
+        assert do.is_contiguous()
+        assert q.stride() == k.stride() == v.stride() == o.stride() == do.stride()
+        dq = torch.empty_like(q)
+        dk = torch.empty_like(k)
+        dv = torch.empty_like(v)
+        BATCH, N_HEAD, N_CTX = q.shape[:3]
+        PRE_BLOCK = 128
+        NUM_WARPS, NUM_STAGES = 4, 5
+        BLOCK_M1, BLOCK_N1, BLOCK_M2, BLOCK_N2 = 32, 128, 128, 32
+        BLK_SLICE_FACTOR = 2
+        RCP_LN2 = 1.4426950408889634  # = 1.0 / ln(2)
+        arg_k = k
+        arg_k = arg_k * (ctx.sm_scale * RCP_LN2)
+        PRE_BLOCK = 128
+        assert N_CTX % PRE_BLOCK == 0
+        pre_grid = (N_CTX // PRE_BLOCK, BATCH * N_HEAD)
+        delta = torch.empty_like(M)
+        _attn_bwd_preprocess[pre_grid](
+            o, do,  #
+            delta,  #
+            BATCH, N_HEAD, N_CTX,  #
+            BLOCK_M=PRE_BLOCK, HEAD_DIM=ctx.HEAD_DIM  #
+        )
+        grid = (N_CTX // BLOCK_N1, 1, BATCH * N_HEAD)
+        _attn_bwd[grid](
+            q, arg_k, v, ctx.sm_scale, do, dq, dk, dv,  #
+            M, delta,  #
+            q.stride(0), q.stride(1), q.stride(2), q.stride(3),  #
+            N_HEAD, N_CTX,  #
+            BLOCK_M1=BLOCK_M1, BLOCK_N1=BLOCK_N1,  #
+            BLOCK_M2=BLOCK_M2, BLOCK_N2=BLOCK_N2,  #
+            BLK_SLICE_FACTOR=BLK_SLICE_FACTOR,  #
+            HEAD_DIM=ctx.HEAD_DIM,  #
+            num_warps=NUM_WARPS,  #
+            num_stages=NUM_STAGES  #
+        )
+
+        return dq, dk, dv, None, None
+
+
+attention = _attention.apply