import math from tinygrad import Tensor, dtypes from tinygrad.helpers import DEBUG from tinygrad.uop.ops import UOp, Ops from extra.thunder.tiny.tk import WARP_THREADS from extra.thunder.tiny.tk.kernel import Kernel from extra.thunder.tiny.tk.tiles import GL, TileLayout NUM_WORKERS = 1 Q_BLOCK_SIZE = 32 KV_BLOCK_SIZE = 32 def _sharded_empty(shape:Tensor, ref:Tensor, axis:int|None) -> Tensor: if not isinstance(ref.device, tuple): return Tensor.empty(*shape, dtype=ref.dtype, device=ref.device) shape = tuple(s // len(ref.device) if i == ref.uop.axis else s for i, s in enumerate(shape)) axis = ref.uop.axis if axis is None else axis return Tensor(Tensor.empty(*shape, dtype=ref.dtype, device=ref.device).uop.unshard(axis), dtype=ref.dtype, device=ref.device) def _sharded_empty_like(ref:Tensor, axis:int|None=None) -> Tensor: return _sharded_empty(ref.shape, ref, axis) def flash_attention(xq, xk, xv, attn_mask:Tensor|None=None, is_causal:bool=False): if len(xq.shape) == 3: xq, xk, xv = xq.unsqueeze(0), xk.unsqueeze(0), xv.unsqueeze(0) odtype = xq.dtype xq, xk, xv = xq.transpose(1, 2).cast(dtypes.bfloat16), xk.transpose(1, 2).cast(dtypes.bfloat16), xv.transpose(1, 2).cast(dtypes.bfloat16) _, N_, _, D_ = xq.shape block_size = max(Q_BLOCK_SIZE, KV_BLOCK_SIZE) assert D_ % block_size == 0, f"embedding dimension must be multiple of block size, got {D_=} {block_size=}" # pad to multiple of block size xq = xq.pad(((0, 0), (0, (block_size - (xq.shape[1] % block_size)) % block_size), (0, 0), (0, 0))) xk = xk.pad(((0, 0), (0, (block_size - (xk.shape[1] % block_size)) % block_size), (0, 0), (0, 0))) xv = xv.pad(((0, 0), (0, (block_size - (xv.shape[1] % block_size)) % block_size), (0, 0), (0, 0))) B, N, H, D = xq.shape H_KV = xk.shape[2] GROUP_SIZE = H // H_KV num_devices = len(xq.device) if isinstance(xq.device, tuple) else 1 B_local = B // num_devices if DEBUG >= 2: print(f"Flash Attention {B=} {B_local=} {N=} {H=} {D=} {H_KV=} {GROUP_SIZE=}") def _custom_forward_impl(ou:UOp, l_vecu:UOp, qu:UOp, ku:UOp, vu:UOp, masku:UOp|None) -> UOp: with Kernel("fa_custom_forward", (H, N // (Q_BLOCK_SIZE*NUM_WORKERS), B_local), NUM_WORKERS * WARP_THREADS) as ker: warp = ker.warp o, q, k, v, l_vec = GL(ou, ker), GL(qu, ker), GL(ku, ker), GL(vu, ker), GL(l_vecu, ker) mask = GL(masku, ker) if masku is not None else None head = ker.blockIdx_x head_kv = head // GROUP_SIZE batch = ker.blockIdx_z q_seq = ker.blockIdx_y * NUM_WORKERS + ker.warpid q_reg_fl = ker.rt((Q_BLOCK_SIZE, D), dtypes.float32) q_reg = ker.rt((Q_BLOCK_SIZE, D), dtypes.bfloat16) q_reg_transposed = ker.rt((D, Q_BLOCK_SIZE), dtypes.bfloat16, TileLayout.COL) k_reg = ker.rt((KV_BLOCK_SIZE, D), dtypes.bfloat16) k_reg_transposed = ker.rt((D, KV_BLOCK_SIZE), dtypes.bfloat16, TileLayout.COL) v_reg = ker.rt((KV_BLOCK_SIZE, D), dtypes.bfloat16, TileLayout.COL) o_reg = ker.rt((D, Q_BLOCK_SIZE), dtypes.float32, TileLayout.COL) o_reg_transposed = ker.rt((Q_BLOCK_SIZE, D), dtypes.float32) att_block = ker.rt((KV_BLOCK_SIZE, Q_BLOCK_SIZE), dtypes.float32, TileLayout.COL) att_block_mma = ker.rt((KV_BLOCK_SIZE, Q_BLOCK_SIZE), dtypes.bfloat16, TileLayout.COL) mask_reg = ker.rt((Q_BLOCK_SIZE, KV_BLOCK_SIZE), dtypes.float32) mask_reg_transposed = ker.rt((KV_BLOCK_SIZE, Q_BLOCK_SIZE), dtypes.float32, TileLayout.COL) max_vec_last = ker.rv(Q_BLOCK_SIZE, dtypes.float32) max_vec = ker.rv(Q_BLOCK_SIZE, dtypes.float32) norm_vec = ker.rv(Q_BLOCK_SIZE, dtypes.float32) scale_vec = ker.rv(Q_BLOCK_SIZE, dtypes.float32) max_vec = warp.neg_inf(max_vec) norm_vec = warp.zero(norm_vec) o_reg = warp.zero(o_reg) scale_vec = warp.ones(scale_vec) # load q tile q_reg_fl = warp.load(q_reg_fl, q, (), (batch, q_seq, head, 0), axis=1) q_reg_fl *= (1.0 / math.sqrt(D)) * (1.0 / math.log(2)) q_reg = warp.copy(q_reg, q_reg_fl) q_reg_transposed = warp.transpose(q_reg_transposed, q_reg) num_kv_blocks = (q_seq + 1) if is_causal else (N // KV_BLOCK_SIZE) for kv_idx in ker.range(num_kv_blocks): k_reg = warp.load(k_reg, k, (), (batch, kv_idx, head_kv, 0), axis=1) v_reg = warp.load(v_reg, v, (), (batch, kv_idx, head_kv, 0), axis=1) # mma qk^t att_block = warp.zero(att_block.after(kv_idx)) k_reg_transposed = warp.transpose(k_reg_transposed, k_reg) att_block = warp.mma_AtB(att_block, k_reg_transposed, q_reg_transposed) # apply attention mask if is_causal: bs_rows, bs_cols, bs_stride = att_block.base_shape.rows, att_block.base_shape.cols, att_block.base_shape.stride q_base = q_seq * Q_BLOCK_SIZE + (warp.laneid % bs_cols) kv_base = kv_idx * KV_BLOCK_SIZE + (warp.laneid // bs_cols) * bs_stride att_block = warp.map(att_block, lambda x, idx: ((kv_base + idx[0]*bs_rows + idx[2]) > (q_base + idx[1]*bs_cols)).alu(Ops.WHERE, UOp.ufix(x._uop, -math.inf), x)) elif mask is not None: mask_reg = warp.load(mask_reg, mask, (), (batch, 0, q_seq, kv_idx), axis=2) mask_reg_transposed = warp.transpose(mask_reg_transposed, mask_reg) att_block += mask_reg_transposed # softmax max_vec_last = warp.copy(max_vec_last.after(kv_idx), max_vec) max_vec = warp.col_reduce(max_vec.after(max_vec_last), att_block, lambda a, b: a.maximum(b), init_value=-math.inf) scale_vec = warp.map(scale_vec.after(max_vec_last, max_vec), lambda _, idx: max_vec_last[*idx] - max_vec[*idx]) scale_vec = scale_vec.exp2() o_reg *= scale_vec norm_vec *= scale_vec att_block -= max_vec att_block = att_block.exp2() norm_vec = warp.col_reduce(norm_vec.after(scale_vec), att_block, lambda a, b: a + b) # mma av att_block_mma = warp.copy(att_block_mma.after(kv_idx, norm_vec), att_block) o_reg = warp.mma_AtB(o_reg, v_reg, att_block_mma) o_reg = ker.endrange() norm_vec = norm_vec.after(o_reg) max_vec = max_vec.after(o_reg) o_reg /= norm_vec o_reg_transposed = warp.transpose(o_reg_transposed, o_reg) o = warp.store(o, o_reg_transposed, (batch, q_seq, head, 0), (), axis=1) norm_vec = norm_vec.after(o) max_vec = max_vec.after(o) max_vec *= math.log(2) norm_vec = norm_vec.log2() * math.log(2) norm_vec += max_vec l_vec = warp.store(l_vec, norm_vec, (batch, head, 0, q_seq), (), axis=2) o = o.after(l_vec) return ker.finish() def custom_forward_causal(ou:UOp, l_vecu:UOp, qu:UOp, ku:UOp, vu:UOp) -> UOp: return _custom_forward_impl(ou, l_vecu, qu, ku, vu, None) def custom_forward_masked(ou:UOp, l_vecu:UOp, qu:UOp, ku:UOp, vu:UOp, masku:UOp) -> UOp: return _custom_forward_impl(ou, l_vecu, qu, ku, vu, masku) def _custom_backward_q_impl(dqu:UOp, dou:UOp, qu:UOp, ku:UOp, vu:UOp, masku:UOp|None, l_vecu:UOp, delta_vecu:UOp) -> UOp: with Kernel("fa_custom_backward_q", (H, N // (Q_BLOCK_SIZE*NUM_WORKERS), B_local), NUM_WORKERS * WARP_THREADS) as ker: warp = ker.warp dq, do, q, k, v = GL(dqu, ker), GL(dou, ker), GL(qu, ker), GL(ku, ker), GL(vu, ker) mask = GL(masku, ker) if masku is not None else None l_vec, delta_vec = GL(l_vecu, ker), GL(delta_vecu, ker) head = ker.blockIdx_x head_kv = head // GROUP_SIZE batch = ker.blockIdx_z q_seq = ker.blockIdx_y * NUM_WORKERS + ker.warpid q_reg_fl = ker.rt((Q_BLOCK_SIZE, D), dtypes.float32) q_reg = ker.rt((Q_BLOCK_SIZE, D), dtypes.bfloat16) q_reg_t = ker.rt((D, Q_BLOCK_SIZE), dtypes.bfloat16, TileLayout.COL) k_reg = ker.rt((KV_BLOCK_SIZE, D), dtypes.bfloat16) k_reg_t = ker.rt((D, KV_BLOCK_SIZE), dtypes.bfloat16, TileLayout.COL) k_reg_col = ker.rt((KV_BLOCK_SIZE, D), dtypes.bfloat16, TileLayout.COL) k_reg_col_t = ker.rt((D, KV_BLOCK_SIZE), dtypes.bfloat16) v_reg = ker.rt((KV_BLOCK_SIZE, D), dtypes.bfloat16) mask_reg = ker.rt((Q_BLOCK_SIZE, KV_BLOCK_SIZE), dtypes.float32) mask_reg_transposed = ker.rt((KV_BLOCK_SIZE, Q_BLOCK_SIZE), dtypes.float32, TileLayout.COL) dq_reg = ker.rt((D, Q_BLOCK_SIZE), dtypes.float32, TileLayout.COL) dq_reg_transposed = ker.rt((Q_BLOCK_SIZE, D), dtypes.float32) do_reg = ker.rt((Q_BLOCK_SIZE, D), dtypes.bfloat16) dp_block = ker.rt((KV_BLOCK_SIZE, Q_BLOCK_SIZE), dtypes.float32, TileLayout.COL) att_block = ker.rt((KV_BLOCK_SIZE, Q_BLOCK_SIZE), dtypes.float32, TileLayout.COL) att_block_mma = ker.rt((KV_BLOCK_SIZE, Q_BLOCK_SIZE), dtypes.bfloat16, TileLayout.COL) l_vec_reg = ker.rv(Q_BLOCK_SIZE, dtypes.float32) delta_vec_reg = ker.rv(Q_BLOCK_SIZE, dtypes.float32) dq_reg = warp.zero(dq_reg) # load q tile q_reg_fl = warp.load(q_reg_fl, q, (), (batch, q_seq, head, 0), axis=1) q_reg_fl *= (1.0 / math.sqrt(D)) * (1.0 / math.log(2)) q_reg = warp.copy(q_reg, q_reg_fl) q_reg_t = warp.transpose(q_reg_t, q_reg) # load do tile do_reg = warp.load(do_reg, do, (), (batch, q_seq, head, 0), axis=1) # load l_vec l_vec_reg = warp.load(l_vec_reg, l_vec, (), (batch, head, 0, q_seq), axis=2) l_vec_reg *= 1.0 / math.log(2) delta_vec_reg = warp.load(delta_vec_reg, delta_vec, (), (batch, head, 0, q_seq), axis=2) num_kv_blocks = (q_seq + 1) if is_causal else (N // KV_BLOCK_SIZE) for kv_idx in ker.range(num_kv_blocks): k_reg = warp.load(k_reg, k, (), (batch, kv_idx, head_kv, 0), axis=1) k_reg_col = warp.load(k_reg_col, k, (), (batch, kv_idx, head_kv, 0), axis=1) v_reg = warp.load(v_reg, v, (), (batch, kv_idx, head_kv, 0), axis=1) k_reg_t = warp.transpose(k_reg_t, k_reg) k_reg_col_t = warp.transpose(k_reg_col_t, k_reg_col) # mma qk^t att_block = warp.zero(att_block.after(kv_idx)) att_block = warp.mma_AtB(att_block, k_reg_t, q_reg_t) # apply attention mask if is_causal: bs_rows, bs_cols, bs_stride = att_block.base_shape.rows, att_block.base_shape.cols, att_block.base_shape.stride q_base = q_seq * Q_BLOCK_SIZE + (warp.laneid % bs_cols) kv_base = kv_idx * KV_BLOCK_SIZE + (warp.laneid // bs_cols) * bs_stride att_block = warp.map(att_block, lambda x, idx: ((kv_base + idx[0]*bs_rows + idx[2]) > (q_base + idx[1]*bs_cols)).alu(Ops.WHERE, UOp.ufix(x._uop, -math.inf), x)) elif mask is not None: mask_reg = warp.load(mask_reg, mask, (), (batch, 0, q_seq, kv_idx), axis=2) mask_reg_transposed = warp.transpose(mask_reg_transposed, mask_reg) att_block += mask_reg_transposed att_block -= l_vec_reg att_block = att_block.exp2() dp_block = warp.zero(dp_block.after(kv_idx, att_block)) dp_block = warp.mma_ABt(dp_block, v_reg, do_reg) dp_block -= delta_vec_reg att_block *= dp_block att_block *= 1.0 / math.sqrt(D) att_block_mma = warp.copy(att_block_mma, att_block) dq_reg = warp.mma_AB(dq_reg, k_reg_col_t, att_block_mma) dq_reg = ker.endrange() dq_reg_transposed = warp.transpose(dq_reg_transposed, dq_reg) dq = warp.store(dq, dq_reg_transposed, (batch, q_seq, head, 0), axis=1) return ker.finish() def custom_backward_q_causal(dqu:UOp, dou:UOp, qu:UOp, ku:UOp, vu:UOp, l_vecu:UOp, delta_vecu:UOp) -> UOp: return _custom_backward_q_impl(dqu, dou, qu, ku, vu, None, l_vecu, delta_vecu) def custom_backward_q_masked(dqu:UOp, dou:UOp, qu:UOp, ku:UOp, vu:UOp, masku:UOp, l_vecu:UOp, delta_vecu:UOp) -> UOp: return _custom_backward_q_impl(dqu, dou, qu, ku, vu, masku, l_vecu, delta_vecu) def _custom_backward_kv_impl(dku:UOp, dvu:UOp, dou:UOp, qu:UOp, ku:UOp, vu:UOp, masku:UOp|None, l_vecu:UOp, delta_vecu:UOp): with Kernel("fa_custom_backward_kv", (H_KV, N // (KV_BLOCK_SIZE*NUM_WORKERS), B_local), NUM_WORKERS * WARP_THREADS) as ker: warp = ker.warp dk, dv, do, q, k, v = GL(dku, ker), GL(dvu, ker), GL(dou, ker), GL(qu, ker), GL(ku, ker), GL(vu, ker) mask = GL(masku, ker) if masku is not None else None l_vec, delta_vec = GL(l_vecu, ker), GL(delta_vecu, ker) head_kv = ker.blockIdx_x batch = ker.blockIdx_z kv_seq = ker.blockIdx_y * NUM_WORKERS + ker.warpid att_smem = ker.st((Q_BLOCK_SIZE, KV_BLOCK_SIZE), dtypes.bfloat16) q_reg = ker.rt((Q_BLOCK_SIZE, D), dtypes.bfloat16) q_reg_t = ker.rt((D, Q_BLOCK_SIZE), dtypes.bfloat16, TileLayout.COL) q_reg_col = ker.rt((Q_BLOCK_SIZE, D), dtypes.bfloat16, TileLayout.COL) k_reg = ker.rt((KV_BLOCK_SIZE, D), dtypes.bfloat16) k_reg_t = ker.rt((D, KV_BLOCK_SIZE), dtypes.bfloat16, TileLayout.COL) v_reg = ker.rt((KV_BLOCK_SIZE, D), dtypes.bfloat16) mask_reg = ker.rt((Q_BLOCK_SIZE, KV_BLOCK_SIZE), dtypes.float32) mask_reg_transposed = ker.rt((KV_BLOCK_SIZE, Q_BLOCK_SIZE), dtypes.float32, TileLayout.COL) dk_reg = ker.rt((KV_BLOCK_SIZE, D), dtypes.float32, TileLayout.COL) dv_reg = ker.rt((KV_BLOCK_SIZE, D), dtypes.float32, TileLayout.COL) do_reg = ker.rt((Q_BLOCK_SIZE, D), dtypes.bfloat16) do_reg_col = ker.rt((Q_BLOCK_SIZE, D), dtypes.bfloat16, TileLayout.COL) dp_block = ker.rt((KV_BLOCK_SIZE, Q_BLOCK_SIZE), dtypes.float32, TileLayout.COL) att_block = ker.rt((KV_BLOCK_SIZE, Q_BLOCK_SIZE), dtypes.float32, TileLayout.COL) att_block_mma = ker.rt((KV_BLOCK_SIZE, Q_BLOCK_SIZE), dtypes.bfloat16, TileLayout.COL) att_block_transposed = ker.rt((Q_BLOCK_SIZE, KV_BLOCK_SIZE), dtypes.bfloat16, TileLayout.COL) att_block_row = ker.rt((Q_BLOCK_SIZE, KV_BLOCK_SIZE), dtypes.bfloat16) l_vec_reg = ker.rv(Q_BLOCK_SIZE, dtypes.float32) delta_vec_reg = ker.rv(Q_BLOCK_SIZE, dtypes.float32) dk_reg = warp.zero(dk_reg) dv_reg = warp.zero(dv_reg) # load kv tile k_reg = warp.load(k_reg, k, (), (batch, kv_seq, head_kv, 0), axis=1) k_reg_t = warp.transpose(k_reg_t, k_reg) v_reg = warp.load(v_reg, v, (), (batch, kv_seq, head_kv, 0), axis=1) q_start = kv_seq if is_causal else 0 for q_idx in ker.range(q_start, N // Q_BLOCK_SIZE): for g in ker.range(GROUP_SIZE): head_q = head_kv * GROUP_SIZE + g q_reg = warp.load(q_reg, q, (), (batch, q_idx, head_q, 0), axis=1) q_reg_col = warp.load(q_reg_col, q, (), (batch, q_idx, head_q, 0), axis=1) do_reg = warp.load(do_reg, do, (), (batch, q_idx, head_q, 0), axis=1) do_reg_col = warp.load(do_reg_col, do, (), (batch, q_idx, head_q, 0), axis=1) q_reg_t = warp.transpose(q_reg_t, q_reg) # load l_vec and delta_vec l_vec_reg = warp.load(l_vec_reg, l_vec, (), (batch, head_q, 0, q_idx), axis=2) l_vec_reg *= 1.0 / math.log(2) delta_vec_reg = warp.load(delta_vec_reg, delta_vec, (), (batch, head_q, 0, q_idx), axis=2) # mma qk^t att_block = warp.zero(att_block.after(g)) att_block = warp.mma_AtB(att_block, k_reg_t, q_reg_t) att_block *= (1.0 / math.sqrt(D)) * (1.0 / math.log(2)) # apply attention mask if is_causal: bs_rows, bs_cols, bs_stride = att_block.base_shape.rows, att_block.base_shape.cols, att_block.base_shape.stride q_base = q_idx * Q_BLOCK_SIZE + (warp.laneid % bs_cols) kv_base = kv_seq * KV_BLOCK_SIZE + (warp.laneid // bs_cols) * bs_stride att_block = warp.map(att_block, lambda x, idx: ((kv_base + idx[0]*bs_rows + idx[2]) > (q_base + idx[1]*bs_cols)).alu(Ops.WHERE, UOp.ufix(x._uop, -math.inf), x)) elif mask is not None: mask_reg = warp.load(mask_reg, mask, (), (batch, 0, q_idx, kv_seq), axis=2) mask_reg_transposed = warp.transpose(mask_reg_transposed, mask_reg) att_block += mask_reg_transposed att_block -= l_vec_reg att_block = att_block.exp2() att_block_mma = warp.copy(att_block_mma, att_block) att_block_transposed = warp.transpose(att_block_transposed, att_block_mma) att_smem = warp.store(att_smem, att_block_transposed) att_block_row = warp.load(att_block_row, att_smem) dv_reg_ = warp.mma_AtB(dv_reg, att_block_row, do_reg_col) dp_block = warp.zero(dp_block.after(g, q_idx, dv_reg_)) dp_block = warp.mma_ABt(dp_block, v_reg, do_reg) dp_block -= delta_vec_reg att_block *= dp_block att_block *= 1.0 / math.sqrt(D) att_block_mma = warp.copy(att_block_mma, att_block) att_block_transposed = warp.transpose(att_block_transposed, att_block_mma) att_smem = warp.store(att_smem, att_block_transposed) att_block_row = warp.load(att_block_row, att_smem) dk_reg = warp.mma_AtB(dk_reg, att_block_row, q_reg_col) dk_reg = ker.endrange(2) dv_reg = dv_reg.after(dk_reg) dv_reg = warp.map(dv_reg, lambda x, idx: x + v_reg[*idx].cast(dtypes.float32) * 1e-30) dk = warp.store(dk, dk_reg, (batch, kv_seq, head_kv, 0), axis=1) dv = warp.store(dv, dv_reg, (batch, kv_seq, head_kv, 0), axis=1) return ker.finish(2) def custom_backward_kv_causal(dku:UOp, dvu:UOp, dou:UOp, qu:UOp, ku:UOp, vu:UOp, l_vecu:UOp, delta_vecu:UOp): return _custom_backward_kv_impl(dku, dvu, dou, qu, ku, vu, None, l_vecu, delta_vecu) def custom_backward_kv_masked(dku:UOp, dvu:UOp, dou:UOp, qu:UOp, ku:UOp, vu:UOp, masku:UOp, l_vecu:UOp, delta_vecu:UOp): return _custom_backward_kv_impl(dku, dvu, dou, qu, ku, vu, masku, l_vecu, delta_vecu) single_device = xq.device[0] if isinstance(xq.device, tuple) else xq.device if is_causal: if attn_mask is not None: raise RuntimeError("cannot set attn_mask when is_causal=True") elif attn_mask is not None: if attn_mask.dtype == dtypes.bool: attn_mask = attn_mask.where(0, -float("inf")) if attn_mask.shape != (B, 1, N, N): attn_mask = attn_mask.expand(B, 1, N, N) if isinstance(xq.device, tuple) and not isinstance(attn_mask.device, tuple): attn_mask = attn_mask.shard(xq.device, axis=0) else: attn_mask = Tensor.zeros((B, 1, N, N), device=single_device, dtype=dtypes.float32) if isinstance(xq.device, tuple): attn_mask = attn_mask.shard(xq.device, axis=0) attn = _sharded_empty_like(xq, axis=0) l_vec = _sharded_empty((B, H, 1, N), xq, axis=0) def grad_causal(gradu:UOp, _) -> tuple[None, None, UOp, UOp, UOp]: grad = Tensor(gradu, device=gradu.device) grad_q = _sharded_empty_like(xq, axis=0) grad_k = _sharded_empty_like(xk, axis=0) grad_v = _sharded_empty_like(xv, axis=0) delta_vec = (grad * attn).sum(-1, dtype=dtypes.float32).transpose(1, 2).unsqueeze(-2).detach() grad_q = Tensor.custom_kernel(grad_q, grad, xq, xk, xv, l_vec, delta_vec, fxn=custom_backward_q_causal)[0] grad_k, grad_v = Tensor.custom_kernel(grad_k, grad_v, grad, xq, xk, xv, l_vec, delta_vec, fxn=custom_backward_kv_causal)[:2] return (None, None, grad_q.uop, grad_k.uop, grad_v.uop) def grad_masked(gradu:UOp, _) -> tuple[None, None, UOp, UOp, UOp, None]: grad = Tensor(gradu, device=gradu.device) grad_q = _sharded_empty_like(xq, axis=0) grad_k = _sharded_empty_like(xk, axis=0) grad_v = _sharded_empty_like(xv, axis=0) delta_vec = (grad * attn).sum(-1, dtype=dtypes.float32).transpose(1, 2).unsqueeze(-2).detach() grad_q = Tensor.custom_kernel(grad_q, grad, xq, xk, xv, attn_mask, l_vec, delta_vec, fxn=custom_backward_q_masked)[0] grad_k, grad_v = Tensor.custom_kernel(grad_k, grad_v, grad, xq, xk, xv, attn_mask, l_vec, delta_vec, fxn=custom_backward_kv_masked)[:2] return (None, None, grad_q.uop, grad_k.uop, grad_v.uop, None) if is_causal: attn, l_vec = Tensor.custom_kernel(attn, l_vec, xq, xk, xv, fxn=custom_forward_causal, grad_fxn=grad_causal)[:2] else: attn, l_vec = Tensor.custom_kernel(attn, l_vec, xq, xk, xv, attn_mask, fxn=custom_forward_masked, grad_fxn=grad_masked)[:2] attn_ = attn[:, :N_, :, :D_] return attn_.transpose(1, 2).cast(odtype)