import torch import math try: import triton import triton.language as tl HAS_TRITON = True except ImportError: HAS_TRITON = False print("please install triton from https://github.com/openai/triton") if HAS_TRITON: ''' this function is modified from https://github.com/ModelTC/lightllm/blob/f093edc20683ac3ea1bca3fb5d8320a0dd36cf7b/lightllm/models/llama/triton_kernel/context_flashattention_nopad.py#L10 ''' @triton.jit def _context_flash_attention_kernel( Q, K, V, sm_scale, B_Start_Loc, B_Seqlen, TMP, alibi_ptr, Out, stride_qbs, stride_qh, stride_qd, stride_kbs, stride_kh, stride_kd, stride_vbs, stride_vh, stride_vd, stride_obs, stride_oh, stride_od, stride_tmp_b, stride_tmp_h, stride_tmp_s, # suggtest set-up 64, 128, 256, 512 BLOCK_M: tl.constexpr, BLOCK_DMODEL: tl.constexpr, BLOCK_N: tl.constexpr, ): batch_id = tl.program_id(0) cur_head = tl.program_id(1) start_m = tl.program_id(2) # initialize offsets offs_n = tl.arange(0, BLOCK_N) offs_d = tl.arange(0, BLOCK_DMODEL) offs_m = start_m * BLOCK_M + tl.arange(0, BLOCK_M) # get batch info cur_batch_seq_len = tl.load(B_Seqlen + batch_id) cur_batch_start_index = tl.load(B_Start_Loc + batch_id) block_start_loc = BLOCK_M * start_m load_p_ptrs = Q + (cur_batch_start_index + offs_m[:, None]) * stride_qbs + cur_head * stride_qh + offs_d[None, :] * stride_qd q = tl.load(load_p_ptrs, mask=offs_m[:, None] < cur_batch_seq_len, other=0.0) k_ptrs = K + offs_n[None, :] * stride_kbs + cur_head * stride_kh + offs_d[:, None] * stride_kd v_ptrs = V + offs_n[:, None] * stride_vbs + cur_head * stride_vh + offs_d[None, :] * stride_vd t_ptrs = TMP + batch_id * stride_tmp_b + cur_head * stride_tmp_h + offs_m * stride_tmp_s m_i = tl.zeros([BLOCK_M], dtype=tl.float32) - float("inf") l_i = tl.zeros([BLOCK_M], dtype=tl.float32) acc = tl.zeros([BLOCK_M, BLOCK_DMODEL], dtype=tl.float32) if alibi_ptr is not None: alibi_m = tl.load(alibi_ptr + cur_head) block_mask = tl.where(block_start_loc < cur_batch_seq_len, 1, 0) for start_n in range(0, block_mask * (start_m + 1) * BLOCK_M, BLOCK_N): start_n = tl.multiple_of(start_n, BLOCK_N) k = tl.load(k_ptrs + (cur_batch_start_index + start_n) * stride_kbs, mask=(start_n + offs_n[None, :]) < cur_batch_seq_len, other=0.0) qk = tl.zeros([BLOCK_M, BLOCK_N], dtype=tl.float32) qk += tl.dot(q, k) qk *= sm_scale if alibi_ptr is not None: alibi_loc = offs_m[:, None] - (start_n + offs_n[None, :]) qk -= alibi_loc * alibi_m qk = tl.where(offs_m[:, None] >= (start_n + offs_n[None, :]), qk, float("-inf")) m_ij = tl.max(qk, 1) p = tl.exp(qk - m_ij[:, None]) l_ij = tl.sum(p, 1) # -- update m_i and l_i m_i_new = tl.maximum(m_i, m_ij) alpha = tl.exp(m_i - m_i_new) beta = tl.exp(m_ij - m_i_new) l_i_new = alpha * l_i + beta * l_ij # -- update output accumulator -- # scale p p_scale = beta / l_i_new p = p * p_scale[:, None] # scale acc acc_scale = l_i / l_i_new * alpha tl.store(t_ptrs, acc_scale) acc_scale = tl.load(t_ptrs) acc = acc * acc_scale[:, None] # update acc v = tl.load(v_ptrs + (cur_batch_start_index + start_n) * stride_vbs, mask=(start_n + offs_n[:, None]) < cur_batch_seq_len, other=0.0) p = p.to(v.dtype) acc += tl.dot(p, v) # update m_i and l_i l_i = l_i_new m_i = m_i_new off_o = (cur_batch_start_index + offs_m[:, None]) * stride_obs + cur_head * stride_oh + offs_d[None, :] * stride_od out_ptrs = Out + off_o tl.store(out_ptrs, acc, mask=offs_m[:, None] < cur_batch_seq_len) return @torch.no_grad() def bloom_context_attn_fwd(q, k, v, o, b_start_loc, b_seq_len, max_input_len, alibi=None): BLOCK = 128 # shape constraints Lq, Lk, Lv = q.shape[-1], k.shape[-1], v.shape[-1] assert Lq == Lk, "context process only supports equal query, key, value length" assert Lk == Lv, "context process only supports equal query, key, value length" assert Lk in {16, 32, 64, 128} sm_scale = 1.0 / math.sqrt(Lk) batch, head = b_seq_len.shape[0], q.shape[1] grid = (batch, head, triton.cdiv(max_input_len, BLOCK)) num_warps = 4 if Lk <= 64 else 8 tmp = torch.empty((batch, head, max_input_len + 256), device=q.device, dtype=torch.float32) _context_flash_attention_kernel[grid]( q, k, v, sm_scale, b_start_loc, b_seq_len, tmp, alibi, o, q.stride(0), q.stride(1), q.stride(2), k.stride(0), k.stride(1), k.stride(2), v.stride(0), v.stride(1), v.stride(2), o.stride(0), o.stride(1), o.stride(2), tmp.stride(0), tmp.stride(1), tmp.stride(2), # manually setting this blcok num, we can use tuning config to futher speed-up BLOCK_M=BLOCK, BLOCK_DMODEL=Lk, BLOCK_N=BLOCK, num_warps=num_warps, num_stages=1, ) return @torch.no_grad() def llama_context_attn_fwd(q, k, v, o, b_start_loc, b_seq_len, max_input_len): BLOCK = 128 # shape constraints Lq, Lk, Lv = q.shape[-1], k.shape[-1], v.shape[-1] assert Lq == Lk, "context process only supports equal query, key, value length" assert Lk == Lv, "context process only supports equal query, key, value length" assert Lk in {16, 32, 64, 128} sm_scale = 1.0 / math.sqrt(Lk) batch, head = b_seq_len.shape[0], q.shape[1] grid = (batch, head, triton.cdiv(max_input_len, BLOCK)) tmp = torch.empty((batch, head, max_input_len + 256), device=q.device, dtype=torch.float32) num_warps = 4 if Lk <= 64 else 8 # num_warps = 4 _context_flash_attention_kernel[grid]( q, k, v, sm_scale, b_start_loc, b_seq_len, tmp, None, o, q.stride(0), q.stride(1), q.stride(2), k.stride(0), k.stride(1), k.stride(2), v.stride(0), v.stride(1), v.stride(2), o.stride(0), o.stride(1), o.stride(2), tmp.stride(0), tmp.stride(1), tmp.stride(2), BLOCK_M=BLOCK, BLOCK_DMODEL=Lk, BLOCK_N=BLOCK, num_warps=num_warps, num_stages=1, ) return