Delete flash_attn_triton.py

flash_attn_triton.py

@@ -1,1112 +0,0 @@
-# Copyright 2022 MosaicML Examples authors
-# SPDX-License-Identifier: Apache-2.0
-
-"""Triton implementation of Flash Attention.
-
-# Copyright (c) 2022, Tri Dao.
-#
-# Licensed under the Apache License, Version 2.0 (the "License");
-# you may not use this file except in compliance with the License.
-# You may obtain a copy of the License at
-#
-#     http://www.apache.org/licenses/LICENSE-2.0
-#
-# Unless required by applicable law or agreed to in writing, software
-# distributed under the License is distributed on an "AS IS" BASIS,
-# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
-# See the License for the specific language governing permissions and
-# limitations under the License.
-
-*Experimental* implementation of FlashAttention in Triton.
-We use the FlashAttention implementation from Phil Tillet a starting point.
-https://github.com/openai/triton/blob/master/python/tutorials/06-fused-attention.py
-
-Changes:
-- Implement both causal and non-causal attention.
-- Implement both self-attention and cross-attention.
-- Support arbitrary seqlens (not just multiples of 128), for both forward and backward.
-- Support all head dimensions up to 128 (not just 16, 32, 64, 128), for both forward and backward.
-- Support attention bias.
-- Speed up the forward pass a bit, and only store the LSE instead of m and l.
-- Make the backward for d=128 much faster by reducing register spilling.
-- Optionally parallelize the backward pass across seqlen_k, to deal with the case of
-small batch size * nheads.
-
-Caution:
-- If you plan to use headdim other than 64 and 128, you should test for race conditions
-(due to the Triton compiler), as done in tests/test_flash_attn.py
-"test_flash_attn_triton_race_condition". I've tested and fixed many race conditions
-for different head dimensions (40, 48, 64, 128, 80, 88, 96), but I'm still not 100% confident
-that there are none left for other head dimensions.
-Differences between this Triton version and the CUDA version:
-- Triton version doesn't support dropout.
-- Triton forward is generally faster than CUDA forward.
-- Triton backward is faster than CUDA backward when batch * nheads is small, and when headdim=64.
-It is slightly slower when headdim=128 and batch * nheads is large.
-- Triton version doesn't yet support different sequence lengths in a batch (i.e., RaggedTensor/NestedTensor).
-"""
-
-import math
-
-import torch
-import triton  # type: ignore (reportMissingImports)
-import triton.language as tl  # type: ignore (reportMissingImports)
-from einops import repeat
-
-
-@triton.autotune(
-    configs=[
-        triton.Config({
-            'BLOCK_M': 128,
-            'BLOCK_N': 128
-        },
-                      num_warps=8,
-                      num_stages=1),
-        # This config has a race condition when EVEN_M == False, disabling it for now.
-        # triton.Config({"BLOCK_M": 64, "BLOCK_N": 64}, num_warps=4, num_stages=1),
-    ],
-    key=[
-        'CACHE_KEY_SEQLEN_Q', 'CACHE_KEY_SEQLEN_K', 'BIAS_TYPE', 'IS_CAUSAL',
-        'BLOCK_HEADDIM'
-    ])
-@triton.heuristics({
-    'EVEN_M': lambda args: args['seqlen_q'] % args['BLOCK_M'] == 0,
-    'EVEN_N': lambda args: args['seqlen_k'] % args['BLOCK_N'] == 0,
-    'EVEN_HEADDIM': lambda args: args['headdim'] == args['BLOCK_HEADDIM'],
-})
-@triton.jit
-def _fwd_kernel(
-    Q,
-    K,
-    V,
-    Bias,
-    Out,
-    Lse,
-    TMP,  # NOTE: TMP is a scratchpad buffer to workaround a compiler bug
-    softmax_scale,
-    stride_qb,
-    stride_qh,
-    stride_qm,
-    stride_kb,
-    stride_kh,
-    stride_kn,
-    stride_vb,
-    stride_vh,
-    stride_vn,
-    stride_bb,
-    stride_bh,
-    stride_bm,
-    stride_ob,
-    stride_oh,
-    stride_om,
-    nheads,
-    seqlen_q,
-    seqlen_k,
-    seqlen_q_rounded,
-    headdim,
-    CACHE_KEY_SEQLEN_Q,
-    CACHE_KEY_SEQLEN_K,
-    BIAS_TYPE: tl.constexpr,
-    IS_CAUSAL: tl.constexpr,
-    BLOCK_HEADDIM: tl.constexpr,
-    EVEN_M: tl.constexpr,
-    EVEN_N: tl.constexpr,
-    EVEN_HEADDIM: tl.constexpr,
-    BLOCK_M: tl.constexpr,
-    BLOCK_N: tl.constexpr,
-):
-    start_m = tl.program_id(0)
-    off_hb = tl.program_id(1)
-    off_b = off_hb // nheads
-    off_h = off_hb % nheads
-    # off_b = tl.program_id(1)
-    # off_h = tl.program_id(2)
-    # off_hb = off_b * nheads + off_h
-    # initialize offsets
-    offs_m = start_m * BLOCK_M + tl.arange(0, BLOCK_M)
-    offs_n = tl.arange(0, BLOCK_N)
-    offs_d = tl.arange(0, BLOCK_HEADDIM)
-    # Initialize pointers to Q, K, V
-    # Adding parenthesis around indexing might use int32 math instead of int64 math?
-    # https://github.com/openai/triton/issues/741
-    # I'm seeing a tiny bit of difference (5-7us)
-    q_ptrs = Q + off_b * stride_qb + off_h * stride_qh + (
-        offs_m[:, None] * stride_qm + offs_d[None, :])
-    k_ptrs = K + off_b * stride_kb + off_h * stride_kh + (
-        offs_n[:, None] * stride_kn + offs_d[None, :])
-    v_ptrs = V + off_b * stride_vb + off_h * stride_vh + (
-        offs_n[:, None] * stride_vn + offs_d[None, :])
-    if BIAS_TYPE == 'vector':
-        b_ptrs = Bias + off_b * stride_bb + off_h * stride_bh + offs_n
-    elif BIAS_TYPE == 'matrix':
-        b_ptrs = Bias + off_b * stride_bb + off_h * stride_bh + (
-            offs_m[:, None] * stride_bm + offs_n[None, :])
-    else:
-        raise ValueError("BIAS_TYPE must be one of {'vector', 'matrix'}")
-    # initialize pointer to m and l
-    t_ptrs = TMP + off_hb * seqlen_q_rounded + offs_m
-    lse_i = tl.zeros([BLOCK_M], dtype=tl.float32) - float('inf')
-    m_i = tl.zeros([BLOCK_M], dtype=tl.float32) - float('inf')
-    acc_o = tl.zeros([BLOCK_M, BLOCK_HEADDIM], dtype=tl.float32)
-    # load q: it will stay in SRAM throughout
-    # [2022-10-30] TD: Triton bug - in the case of EVEN_M=True and EVEN_N=False, if we just call
-    # tl.load(q_ptrs), we get the wrong output!
-    if EVEN_M & EVEN_N:
-        if EVEN_HEADDIM:
-            q = tl.load(q_ptrs)
-        else:
-            q = tl.load(q_ptrs, mask=offs_d[None, :] < headdim, other=0.0)
-    else:
-        if EVEN_HEADDIM:
-            q = tl.load(q_ptrs, mask=offs_m[:, None] < seqlen_q, other=0.0)
-        else:
-            q = tl.load(q_ptrs,
-                        mask=(offs_m[:, None] < seqlen_q) &
-                        (offs_d[None, :] < headdim),
-                        other=0.0)
-    # loop over k, v and update accumulator
-    end_n = seqlen_k if not IS_CAUSAL else tl.minimum(
-        (start_m + 1) * BLOCK_M, seqlen_k)
-    for start_n in range(0, end_n, BLOCK_N):
-        start_n = tl.multiple_of(start_n, BLOCK_N)
-        # -- compute qk ----
-        if EVEN_N & EVEN_M:  # If we just do "if EVEN_N", there seems to be some race condition
-            if EVEN_HEADDIM:
-                k = tl.load(k_ptrs + start_n * stride_kn)
-            else:
-                k = tl.load(k_ptrs + start_n * stride_kn,
-                            mask=offs_d[None, :] < headdim,
-                            other=0.0)
-        else:
-            if EVEN_HEADDIM:
-                k = tl.load(k_ptrs + start_n * stride_kn,
-                            mask=(start_n + offs_n)[:, None] < seqlen_k,
-                            other=0.0)
-            else:
-                k = tl.load(k_ptrs + start_n * stride_kn,
-                            mask=((start_n + offs_n)[:, None] < seqlen_k) &
-                            (offs_d[None, :] < headdim),
-                            other=0.0)
-        qk = tl.zeros([BLOCK_M, BLOCK_N], dtype=tl.float32)
-        qk += tl.dot(q, tl.trans(k))
-        # Trying to combine the two masks seem to make the result wrong
-        if not EVEN_N:  # Need to mask out otherwise the softmax is wrong
-            qk += tl.where((start_n + offs_n)[None, :] < seqlen_k, 0,
-                           float('-inf'))
-        if IS_CAUSAL:
-            qk += tl.where(offs_m[:, None] >= (start_n + offs_n)[None, :], 0,
-                           float('-inf'))
-        if BIAS_TYPE != 'none':
-            if BIAS_TYPE == 'vector':
-                if EVEN_N:
-                    bias = tl.load(b_ptrs + start_n).to(tl.float32)
-                else:
-                    bias = tl.load(b_ptrs + start_n,
-                                   mask=(start_n + offs_n) < seqlen_k,
-                                   other=0.0).to(tl.float32)
-                bias = bias[None, :]
-            elif BIAS_TYPE == 'matrix':
-                if EVEN_M & EVEN_N:
-                    bias = tl.load(b_ptrs + start_n).to(tl.float32)
-                else:
-                    bias = tl.load(b_ptrs + start_n,
-                                   mask=(offs_m[:, None] < seqlen_q) &
-                                   ((start_n + offs_n)[None, :] < seqlen_k),
-                                   other=0.0).to(tl.float32)
-            else:
-                raise ValueError(
-                    "BIAS_TYPE must be one of {'vector', 'matrix'}")
-            # Slightly faster to multiply the softmax_scale in the tl.exp below since the compiler
-            # can then fuse the mult and add into an fma instruction. But if we have bias we need to
-            # to multiply with softmax_scale here.
-            qk = qk * softmax_scale + bias
-            m_ij = tl.maximum(tl.max(qk, 1), lse_i)
-            p = tl.exp(qk - m_ij[:, None])
-        else:
-            m_ij = tl.maximum(tl.max(qk, 1) * softmax_scale, lse_i)
-            p = tl.exp(qk * softmax_scale - m_ij[:, None])
-        l_ij = tl.sum(p, 1)
-
-        # scale acc_o
-        acc_o_scale = tl.exp(m_i - m_ij)
-
-        # # -- update output accumulator --
-        # BUG: have to store and immediately load
-        tl.store(t_ptrs, acc_o_scale)
-        acc_o_scale = tl.load(t_ptrs)
-        acc_o = acc_o * acc_o_scale[:, None]
-        # update acc_o
-        if EVEN_N & EVEN_M:  # If we just do "if EVEN_N", there seems to be some race condition
-            if EVEN_HEADDIM:
-                v = tl.load(v_ptrs + start_n * stride_vn)
-            else:
-                v = tl.load(v_ptrs + start_n * stride_vn,
-                            mask=offs_d[None, :] < headdim,
-                            other=0.0)
-        else:
-            if EVEN_HEADDIM:
-                v = tl.load(v_ptrs + start_n * stride_vn,
-                            mask=(start_n + offs_n)[:, None] < seqlen_k,
-                            other=0.0)
-            else:
-                v = tl.load(v_ptrs + start_n * stride_vn,
-                            mask=((start_n + offs_n)[:, None] < seqlen_k) &
-                            (offs_d[None, :] < headdim),
-                            other=0.0)
-        p = p.to(v.dtype)
-        acc_o += tl.dot(p, v)
-
-        # -- update statistics
-        m_i = m_ij
-        l_i_new = tl.exp(lse_i - m_ij) + l_ij
-        lse_i = m_ij + tl.log(l_i_new)
-
-    o_scale = tl.exp(m_i - lse_i)
-    # BUG: have to store and immediately load
-    tl.store(t_ptrs, o_scale)
-    o_scale = tl.load(t_ptrs)
-    acc_o = acc_o * o_scale[:, None]
-    # rematerialize offsets to save registers
-    start_m = tl.program_id(0)
-    offs_m = start_m * BLOCK_M + tl.arange(0, BLOCK_M)
-    # write back l and m
-    lse_ptrs = Lse + off_hb * seqlen_q_rounded + offs_m
-    tl.store(lse_ptrs, lse_i)
-    # initialize pointers to output
-    offs_n = tl.arange(0, BLOCK_HEADDIM)
-    out_ptrs = Out + off_b * stride_ob + off_h * stride_oh + (
-        offs_m[:, None] * stride_om + offs_n[None, :])
-    if EVEN_M:
-        if EVEN_HEADDIM:
-            tl.store(out_ptrs, acc_o)
-        else:
-            tl.store(out_ptrs, acc_o, mask=offs_d[None, :] < headdim)
-    else:
-        if EVEN_HEADDIM:
-            tl.store(out_ptrs, acc_o, mask=offs_m[:, None] < seqlen_q)
-        else:
-            tl.store(out_ptrs,
-                     acc_o,
-                     mask=(offs_m[:, None] < seqlen_q) &
-                     (offs_d[None, :] < headdim))
-
-
-@triton.jit
-def _bwd_preprocess_do_o_dot(
-    Out,
-    DO,
-    Delta,
-    stride_ob,
-    stride_oh,
-    stride_om,
-    stride_dob,
-    stride_doh,
-    stride_dom,
-    nheads,
-    seqlen_q,
-    seqlen_q_rounded,
-    headdim,
-    BLOCK_M: tl.constexpr,
-    BLOCK_HEADDIM: tl.constexpr,
-):
-    start_m = tl.program_id(0)
-    off_hb = tl.program_id(1)
-    off_b = off_hb // nheads
-    off_h = off_hb % nheads
-    # initialize offsets
-    offs_m = start_m * BLOCK_M + tl.arange(0, BLOCK_M)
-    offs_d = tl.arange(0, BLOCK_HEADDIM)
-    # load
-    o = tl.load(Out + off_b * stride_ob + off_h * stride_oh +
-                offs_m[:, None] * stride_om + offs_d[None, :],
-                mask=(offs_m[:, None] < seqlen_q) & (offs_d[None, :] < headdim),
-                other=0.0).to(tl.float32)
-    do = tl.load(DO + off_b * stride_dob + off_h * stride_doh +
-                 offs_m[:, None] * stride_dom + offs_d[None, :],
-                 mask=(offs_m[:, None] < seqlen_q) &
-                 (offs_d[None, :] < headdim),
-                 other=0.0).to(tl.float32)
-    delta = tl.sum(o * do, axis=1)
-    # write-back
-    tl.store(Delta + off_hb * seqlen_q_rounded + offs_m, delta)
-
-
-@triton.jit
-def _bwd_kernel_one_col_block(
-    start_n,
-    Q,
-    K,
-    V,
-    Bias,
-    DO,
-    DQ,
-    DK,
-    DV,
-    LSE,
-    D,
-    softmax_scale,
-    stride_qm,
-    stride_kn,
-    stride_vn,
-    stride_bm,
-    stride_dom,
-    stride_dqm,
-    stride_dkn,
-    stride_dvn,
-    seqlen_q,
-    seqlen_k,
-    headdim,
-    ATOMIC_ADD: tl.constexpr,
-    BIAS_TYPE: tl.constexpr,
-    IS_CAUSAL: tl.constexpr,
-    BLOCK_HEADDIM: tl.constexpr,
-    EVEN_M: tl.constexpr,
-    EVEN_N: tl.constexpr,
-    EVEN_HEADDIM: tl.constexpr,
-    BLOCK_M: tl.constexpr,
-    BLOCK_N: tl.constexpr,
-):
-    # We need to make sure begin_m is a multiple of BLOCK_M (not BLOCK_N)
-    begin_m = 0 if not IS_CAUSAL else ((start_n * BLOCK_N) // BLOCK_M) * BLOCK_M
-    # initialize row/col offsets
-    offs_qm = begin_m + tl.arange(0, BLOCK_M)
-    offs_n = start_n * BLOCK_N + tl.arange(0, BLOCK_N)
-    offs_m = tl.arange(0, BLOCK_M)
-    offs_d = tl.arange(0, BLOCK_HEADDIM)
-    # initialize pointers to value-like data
-    q_ptrs = Q + (offs_qm[:, None] * stride_qm + offs_d[None, :])
-    k_ptrs = K + (offs_n[:, None] * stride_kn + offs_d[None, :])
-    v_ptrs = V + (offs_n[:, None] * stride_vn + offs_d[None, :])
-    do_ptrs = DO + (offs_qm[:, None] * stride_dom + offs_d[None, :])
-    dq_ptrs = DQ + (offs_qm[:, None] * stride_dqm + offs_d[None, :])
-    if BIAS_TYPE == 'vector':
-        b_ptrs = Bias + offs_n
-    elif BIAS_TYPE == 'matrix':
-        b_ptrs = Bias + (offs_qm[:, None] * stride_bm + offs_n[None, :])
-    else:
-        raise ValueError("BIAS_TYPE must be one of {'vector', 'matrix'}")
-    # initialize dv and dk
-    dv = tl.zeros([BLOCK_N, BLOCK_HEADDIM], dtype=tl.float32)
-    dk = tl.zeros([BLOCK_N, BLOCK_HEADDIM], dtype=tl.float32)
-    # k and v stay in SRAM throughout
-    # [2022-10-30] TD: Same bug as the fwd. In the case of EVEN_N=True and EVEN_M=False,
-    # if we just call tl.load(k_ptrs), we get the wrong output!
-    if EVEN_N & EVEN_M:
-        if EVEN_HEADDIM:
-            k = tl.load(k_ptrs)
-            v = tl.load(v_ptrs)
-        else:
-            k = tl.load(k_ptrs, mask=offs_d[None, :] < headdim, other=0.0)
-            v = tl.load(v_ptrs, mask=offs_d[None, :] < headdim, other=0.0)
-    else:
-        if EVEN_HEADDIM:
-            k = tl.load(k_ptrs, mask=offs_n[:, None] < seqlen_k, other=0.0)
-            v = tl.load(v_ptrs, mask=offs_n[:, None] < seqlen_k, other=0.0)
-        else:
-            k = tl.load(k_ptrs,
-                        mask=(offs_n[:, None] < seqlen_k) &
-                        (offs_d[None, :] < headdim),
-                        other=0.0)
-            v = tl.load(v_ptrs,
-                        mask=(offs_n[:, None] < seqlen_k) &
-                        (offs_d[None, :] < headdim),
-                        other=0.0)
-    # loop over rows
-    num_block_m = tl.cdiv(seqlen_q, BLOCK_M)
-    for start_m in range(begin_m, num_block_m * BLOCK_M, BLOCK_M):
-        start_m = tl.multiple_of(start_m, BLOCK_M)
-        offs_m_curr = start_m + offs_m
-        # load q, k, v, do on-chip
-        # Same bug as below. Otherwise gives wrong result for headdim=40, seqlen=(128, 117)
-        if EVEN_M & EVEN_HEADDIM:
-            q = tl.load(q_ptrs)
-        else:
-            if EVEN_HEADDIM:
-                q = tl.load(q_ptrs,
-                            mask=offs_m_curr[:, None] < seqlen_q,
-                            other=0.0)
-            else:
-                q = tl.load(q_ptrs,
-                            mask=(offs_m_curr[:, None] < seqlen_q) &
-                            (offs_d[None, :] < headdim),
-                            other=0.0)
-        # recompute p = softmax(qk, dim=-1).T
-        qk = tl.dot(q, tl.trans(k))
-        # Trying to combine the two masks seem to make the result wrong
-        if not EVEN_N:  # Need to mask out otherwise the softmax is wrong
-            qk = tl.where(offs_n[None, :] < seqlen_k, qk, float('-inf'))
-        if IS_CAUSAL:
-            qk = tl.where(offs_m_curr[:, None] >= (offs_n[None, :]), qk,
-                          float('-inf'))
-        if BIAS_TYPE != 'none':
-            if BIAS_TYPE == 'vector':
-                if EVEN_N:
-                    bias = tl.load(b_ptrs).to(tl.float32)
-                else:
-                    bias = tl.load(b_ptrs, mask=offs_n < seqlen_k,
-                                   other=0.0).to(tl.float32)
-                bias = bias[None, :]
-            elif BIAS_TYPE == 'matrix':
-                if EVEN_M & EVEN_N:
-                    bias = tl.load(b_ptrs).to(tl.float32)
-                else:
-                    bias = tl.load(b_ptrs,
-                                   mask=(offs_m_curr[:, None] < seqlen_q) &
-                                   (offs_n[None, :] < seqlen_k),
-                                   other=0.0).to(tl.float32)
-            else:
-                raise ValueError(
-                    "BIAS_TYPE must be one of {'vector', 'matrix'}")
-            qk = qk * softmax_scale + bias
-        # There seems to be a race condition when headdim=48/96, and dq, dk, dv are wrong.
-        # Also wrong for headdim=64.
-        if not (EVEN_M & EVEN_HEADDIM):
-            tl.debug_barrier()
-        lse_i = tl.load(LSE + offs_m_curr)
-        if BIAS_TYPE == 'none':
-            p = tl.exp(qk * softmax_scale - lse_i[:, None])
-        else:
-            p = tl.exp(qk - lse_i[:, None])
-        # compute dv
-        # [2022-10-30] TD: A Triton bug: if EVEN_M=True and EVEN_HEADDIM=False, if we call
-        # do = tl.load(do_ptrs, mask=offs_d[None, :] < headdim, other=0.0), we get wrong outputs
-        # in the case of headdim=48/96, seqlen_q & seqlen_k >= 512. If headdim=40 or seqlen < 512,
-        # the output is correct.
-        if EVEN_M & EVEN_HEADDIM:
-            do = tl.load(do_ptrs)
-        else:
-            # [2022-11-01] TD: Triton bug, there's a race condition if we just use m_mask and not d_mask.
-            do = tl.load(do_ptrs,
-                         mask=(offs_m_curr[:, None] < seqlen_q) &
-                         (offs_d[None, :] < headdim),
-                         other=0.0)
-        # if EVEN_M:
-        #     if EVEN_HEADDIM:
-        #         do = tl.load(do_ptrs)
-        #     else:
-        #         do = tl.load(do_ptrs, mask=offs_d[None, :] < headdim, other=0.0)
-        # else:
-        #     if EVEN_HEADDIM:
-        #         do = tl.load(do_ptrs, mask=offs_m_curr[:, None] < seqlen_q, other=0.0)
-        #     else:
-        #         do = tl.load(do_ptrs, mask=(offs_m_curr[:, None] < seqlen_q)
-        #                                    & (offs_d[None, :] < headdim), other=0.0)
-        dv += tl.dot(tl.trans(p).to(do.dtype), do)
-        # compute dp = dot(v, do)
-        # There seems to be a race condition when headdim=48/96, and dq, dk are wrong.
-        # Also wrong for headdim=128, seqlen=(108, 256), and ATOMIC_ADD=True
-        # Also wrong for headdim=64, seqlen=(1023, 1024), and ATOMIC_ADD=False
-        if not (EVEN_M & EVEN_HEADDIM):
-            tl.debug_barrier()
-        dp = tl.dot(do, v, trans_b=True)
-        # There's a race condition for headdim=48
-        if not EVEN_HEADDIM:
-            tl.debug_barrier()
-        # compute ds = p * (dp - delta[:, None])
-        # Putting the subtraction after the dp matmul (instead of before) is slightly faster
-        Di = tl.load(D + offs_m_curr)
-        # Converting ds to q.dtype here reduces register pressure and makes it much faster
-        # for BLOCK_HEADDIM=128
-        ds = (p * (dp - Di[:, None]) * softmax_scale).to(q.dtype)
-        # compute dk = dot(ds.T, q)
-        dk += tl.dot(tl.trans(ds), q)
-        # compute dq
-        if not ATOMIC_ADD:
-            if EVEN_M & EVEN_HEADDIM:  # Race condition if we just do EVEN_M
-                dq = tl.load(dq_ptrs, eviction_policy='evict_last')
-                dq += tl.dot(ds, k)
-                tl.store(dq_ptrs, dq, eviction_policy='evict_last')
-            else:
-                if EVEN_HEADDIM:
-                    dq = tl.load(dq_ptrs,
-                                 mask=offs_m_curr[:, None] < seqlen_q,
-                                 other=0.0,
-                                 eviction_policy='evict_last')
-                    dq += tl.dot(ds, k)
-                    tl.store(dq_ptrs,
-                             dq,
-                             mask=offs_m_curr[:, None] < seqlen_q,
-                             eviction_policy='evict_last')
-                else:
-                    dq = tl.load(dq_ptrs,
-                                 mask=(offs_m_curr[:, None] < seqlen_q) &
-                                 (offs_d[None, :] < headdim),
-                                 other=0.0,
-                                 eviction_policy='evict_last')
-                    dq += tl.dot(ds, k)
-                    tl.store(dq_ptrs,
-                             dq,
-                             mask=(offs_m_curr[:, None] < seqlen_q) &
-                             (offs_d[None, :] < headdim),
-                             eviction_policy='evict_last')
-        else:  # If we're parallelizing across the seqlen_k dimension
-            dq = tl.dot(ds, k)
-            if EVEN_M & EVEN_HEADDIM:  # Race condition if we just do EVEN_M
-                tl.atomic_add(dq_ptrs, dq)
-            else:
-                if EVEN_HEADDIM:
-                    tl.atomic_add(dq_ptrs,
-                                  dq,
-                                  mask=offs_m_curr[:, None] < seqlen_q)
-                else:
-                    tl.atomic_add(dq_ptrs,
-                                  dq,
-                                  mask=(offs_m_curr[:, None] < seqlen_q) &
-                                  (offs_d[None, :] < headdim))
-        # increment pointers
-        dq_ptrs += BLOCK_M * stride_dqm
-        q_ptrs += BLOCK_M * stride_qm
-        do_ptrs += BLOCK_M * stride_dom
-        if BIAS_TYPE == 'matrix':
-            b_ptrs += BLOCK_M * stride_bm
-    # write-back
-    dv_ptrs = DV + (offs_n[:, None] * stride_dvn + offs_d[None, :])
-    dk_ptrs = DK + (offs_n[:, None] * stride_dkn + offs_d[None, :])
-    # [2022-11-01] TD: Same bug. In the case of EVEN_N=True and EVEN_M=False,
-    # if we just call tl.store(dv_ptrs), there's a race condition
-    if EVEN_N & EVEN_M:
-        if EVEN_HEADDIM:
-            tl.store(dv_ptrs, dv)
-            tl.store(dk_ptrs, dk)
-        else:
-            tl.store(dv_ptrs, dv, mask=offs_d[None, :] < headdim)
-            tl.store(dk_ptrs, dk, mask=offs_d[None, :] < headdim)
-    else:
-        if EVEN_HEADDIM:
-            tl.store(dv_ptrs, dv, mask=offs_n[:, None] < seqlen_k)
-            tl.store(dk_ptrs, dk, mask=offs_n[:, None] < seqlen_k)
-        else:
-            tl.store(dv_ptrs,
-                     dv,
-                     mask=(offs_n[:, None] < seqlen_k) &
-                     (offs_d[None, :] < headdim))
-            tl.store(dk_ptrs,
-                     dk,
-                     mask=(offs_n[:, None] < seqlen_k) &
-                     (offs_d[None, :] < headdim))
-
-
-def init_to_zero(name):
-    return lambda nargs: nargs[name].zero_()
-
-
-@triton.autotune(
-    configs=[
-        triton.Config(
-            {
-                'BLOCK_M': 128,
-                'BLOCK_N': 128,
-                'SEQUENCE_PARALLEL': False
-            },
-            num_warps=8,
-            num_stages=1,
-            pre_hook=init_to_zero('DQ')),
-        triton.Config(
-            {
-                'BLOCK_M': 128,
-                'BLOCK_N': 128,
-                'SEQUENCE_PARALLEL': True
-            },
-            num_warps=8,
-            num_stages=1,
-            pre_hook=init_to_zero('DQ')),
-        # Other configs seem to give wrong results when seqlen_q % 128 != 0, disabling them for now
-        # # Kernel is buggy (give wrong result) if we set BLOCK_m=128, BLOCK_n=64, num_warps=*4*
-        # triton.Config({"BLOCK_M": 128, "BLOCK_N": 64, "SEQUENCE_PARALLEL": False}, num_warps=8, num_stages=1, pre_hook=init_to_zero('DQ')),
-        # triton.Config({"BLOCK_M": 128, "BLOCK_N": 64, "SEQUENCE_PARALLEL": True}, num_warps=8, num_stages=1, pre_hook=init_to_zero('DQ')),
-        # triton.Config({"BLOCK_M": 64, "BLOCK_N": 64, "SEQUENCE_PARALLEL": False}, num_warps=4, num_stages=1, pre_hook=init_to_zero('DQ')),
-        # triton.Config({"BLOCK_M": 64, "BLOCK_N": 64, "SEQUENCE_PARALLEL": True}, num_warps=4, num_stages=1, pre_hook=init_to_zero('DQ')),
-    ],
-    key=[
-        'CACHE_KEY_SEQLEN_Q', 'CACHE_KEY_SEQLEN_K', 'BIAS_TYPE', 'IS_CAUSAL',
-        'BLOCK_HEADDIM'
-    ],
-)
-@triton.heuristics({
-    'EVEN_M': lambda args: args['seqlen_q'] % args['BLOCK_M'] == 0,
-    'EVEN_N': lambda args: args['seqlen_k'] % args['BLOCK_N'] == 0,
-    'EVEN_HEADDIM': lambda args: args['headdim'] == args['BLOCK_HEADDIM'],
-})
-@triton.jit
-def _bwd_kernel(
-    Q,
-    K,
-    V,
-    Bias,
-    DO,
-    DQ,
-    DK,
-    DV,
-    LSE,
-    D,
-    softmax_scale,
-    stride_qb,
-    stride_qh,
-    stride_qm,
-    stride_kb,
-    stride_kh,
-    stride_kn,
-    stride_vb,
-    stride_vh,
-    stride_vn,
-    stride_bb,
-    stride_bh,
-    stride_bm,
-    stride_dob,
-    stride_doh,
-    stride_dom,
-    stride_dqb,
-    stride_dqh,
-    stride_dqm,
-    stride_dkb,
-    stride_dkh,
-    stride_dkn,
-    stride_dvb,
-    stride_dvh,
-    stride_dvn,
-    nheads,
-    seqlen_q,
-    seqlen_k,
-    seqlen_q_rounded,
-    headdim,
-    CACHE_KEY_SEQLEN_Q,
-    CACHE_KEY_SEQLEN_K,
-    BIAS_TYPE: tl.constexpr,
-    IS_CAUSAL: tl.constexpr,
-    BLOCK_HEADDIM: tl.constexpr,
-    SEQUENCE_PARALLEL: tl.constexpr,
-    EVEN_M: tl.constexpr,
-    EVEN_N: tl.constexpr,
-    EVEN_HEADDIM: tl.constexpr,
-    BLOCK_M: tl.constexpr,
-    BLOCK_N: tl.constexpr,
-):
-    off_hb = tl.program_id(1)
-    off_b = off_hb // nheads
-    off_h = off_hb % nheads
-    # offset pointers for batch/head
-    Q += off_b * stride_qb + off_h * stride_qh
-    K += off_b * stride_kb + off_h * stride_kh
-    V += off_b * stride_vb + off_h * stride_vh
-    DO += off_b * stride_dob + off_h * stride_doh
-    DQ += off_b * stride_dqb + off_h * stride_dqh
-    DK += off_b * stride_dkb + off_h * stride_dkh
-    DV += off_b * stride_dvb + off_h * stride_dvh
-    if BIAS_TYPE != 'none':
-        Bias += off_b * stride_bb + off_h * stride_bh
-    # pointer to row-wise quantities in value-like data
-    D += off_hb * seqlen_q_rounded
-    LSE += off_hb * seqlen_q_rounded
-    if not SEQUENCE_PARALLEL:
-        num_block_n = tl.cdiv(seqlen_k, BLOCK_N)
-        for start_n in range(0, num_block_n):
-            _bwd_kernel_one_col_block(start_n,
-                                      Q,
-                                      K,
-                                      V,
-                                      Bias,
-                                      DO,
-                                      DQ,
-                                      DK,
-                                      DV,
-                                      LSE,
-                                      D,
-                                      softmax_scale,
-                                      stride_qm,
-                                      stride_kn,
-                                      stride_vn,
-                                      stride_bm,
-                                      stride_dom,
-                                      stride_dqm,
-                                      stride_dkn,
-                                      stride_dvn,
-                                      seqlen_q,
-                                      seqlen_k,
-                                      headdim,
-                                      ATOMIC_ADD=False,
-                                      BIAS_TYPE=BIAS_TYPE,
-                                      IS_CAUSAL=IS_CAUSAL,
-                                      BLOCK_HEADDIM=BLOCK_HEADDIM,
-                                      EVEN_M=EVEN_M,
-                                      EVEN_N=EVEN_N,
-                                      EVEN_HEADDIM=EVEN_HEADDIM,
-                                      BLOCK_M=BLOCK_M,
-                                      BLOCK_N=BLOCK_N)
-    else:
-        start_n = tl.program_id(0)
-        _bwd_kernel_one_col_block(start_n,
-                                  Q,
-                                  K,
-                                  V,
-                                  Bias,
-                                  DO,
-                                  DQ,
-                                  DK,
-                                  DV,
-                                  LSE,
-                                  D,
-                                  softmax_scale,
-                                  stride_qm,
-                                  stride_kn,
-                                  stride_vn,
-                                  stride_bm,
-                                  stride_dom,
-                                  stride_dqm,
-                                  stride_dkn,
-                                  stride_dvn,
-                                  seqlen_q,
-                                  seqlen_k,
-                                  headdim,
-                                  ATOMIC_ADD=True,
-                                  BIAS_TYPE=BIAS_TYPE,
-                                  IS_CAUSAL=IS_CAUSAL,
-                                  BLOCK_HEADDIM=BLOCK_HEADDIM,
-                                  EVEN_M=EVEN_M,
-                                  EVEN_N=EVEN_N,
-                                  EVEN_HEADDIM=EVEN_HEADDIM,
-                                  BLOCK_M=BLOCK_M,
-                                  BLOCK_N=BLOCK_N)
-
-
-def _flash_attn_forward(q, k, v, bias=None, causal=False, softmax_scale=None):
-    # shape constraints
-    batch, seqlen_q, nheads, d = q.shape
-    _, seqlen_k, _, _ = k.shape
-    assert k.shape == (batch, seqlen_k, nheads, d)
-    assert v.shape == (batch, seqlen_k, nheads, d)
-    assert d <= 128, 'FlashAttention only support head dimensions up to 128'
-    assert q.dtype == k.dtype == v.dtype, 'All tensors must have the same type'
-    assert q.dtype in [torch.float16,
-                       torch.bfloat16], 'Only support fp16 and bf16'
-    assert q.is_cuda and k.is_cuda and v.is_cuda
-    softmax_scale = softmax_scale or 1.0 / math.sqrt(d)
-
-    has_bias = bias is not None
-    bias_type = 'none'
-    if has_bias:
-        assert bias.dtype in [q.dtype, torch.float]
-        assert bias.is_cuda
-        assert bias.dim() == 4
-        if bias.stride(-1) != 1:
-            bias = bias.contiguous()
-        if bias.shape[2:] == (1, seqlen_k):
-            bias_type = 'vector'
-        elif bias.shape[2:] == (seqlen_q, seqlen_k):
-            bias_type = 'matrix'
-        else:
-            raise RuntimeError('Last 2 dimensions of bias must be (1, seqlen_k)'
-                               ' or (seqlen_q, seqlen_k)')
-        if bias.shape[:2] == (1, nheads):
-            bias = repeat(bias, '1 h ... -> b h ...', b=batch)
-        elif bias.shape[:2] == (batch, 1):
-            bias = repeat(bias, 'b 1 ... -> b h ...', h=nheads)
-        elif bias.shape[:2] == (1, 1):
-            bias = repeat(bias, '1 h ... -> b h ...', b=batch)
-            bias = repeat(bias, 'b 1 ... -> b h ...', h=nheads)
-        assert bias.shape[:2] == (
-            batch, nheads
-        ), f'First 2 dimensions of bias must be broadcastible to (batch, nheads) = ({batch, nheads}). Bias has shape: {bias.shape}'
-    assert bias is not None  # for type checking
-    bias_strides = (bias.stride(0), bias.stride(1),
-                    bias.stride(2)) if has_bias else (0, 0, 0)
-
-    seqlen_q_rounded = math.ceil(seqlen_q / 128) * 128
-    lse = torch.empty((batch, nheads, seqlen_q_rounded),
-                      device=q.device,
-                      dtype=torch.float32)
-    tmp = torch.empty((batch, nheads, seqlen_q_rounded),
-                      device=q.device,
-                      dtype=torch.float32)
-    o = torch.empty_like(q)
-
-    BLOCK_HEADDIM = max(triton.next_power_of_2(d), 16)
-    # BLOCK = 128
-    # num_warps = 4 if d <= 64 else 8
-    grid = lambda META: (triton.cdiv(seqlen_q, META['BLOCK_M']), batch * nheads)
-    _fwd_kernel[grid](  # type: ignore
-        q,
-        k,
-        v,
-        bias,
-        o,
-        lse,
-        tmp,
-        softmax_scale,
-        q.stride(0),
-        q.stride(2),
-        q.stride(1),
-        k.stride(0),
-        k.stride(2),
-        k.stride(1),
-        v.stride(0),
-        v.stride(2),
-        v.stride(1),
-        *bias_strides,
-        o.stride(0),
-        o.stride(2),
-        o.stride(1),
-        nheads,
-        seqlen_q,
-        seqlen_k,
-        seqlen_q_rounded,
-        d,
-        seqlen_q // 32,
-        seqlen_k // 32,  # key for triton cache (limit number of compilations)
-        # Can't use kwargs here because triton autotune expects key to be args, not kwargs
-        # IS_CAUSAL=causal, BLOCK_HEADDIM=d,
-        bias_type,
-        causal,
-        BLOCK_HEADDIM,
-        # BLOCK_M=BLOCK, BLOCK_N=BLOCK,
-        # num_warps=num_warps,
-        # num_stages=1,
-    )
-    return o, lse, softmax_scale  # softmax_scale could have been updated
-
-
-def _flash_attn_backward(do,
-                         q,
-                         k,
-                         v,
-                         o,
-                         lse,
-                         dq,
-                         dk,
-                         dv,
-                         bias=None,
-                         causal=False,
-                         softmax_scale=None):
-    # Make sure that the last dimension is contiguous
-    if do.stride(-1) != 1:
-        do = do.contiguous()
-    batch, seqlen_q, nheads, d = q.shape
-    _, seqlen_k, _, _ = k.shape
-    # assert d in {16, 32, 64, 128}
-    assert d <= 128
-    seqlen_q_rounded = math.ceil(seqlen_q / 128) * 128
-    assert lse.shape == (batch, nheads, seqlen_q_rounded)
-    assert q.stride(-1) == k.stride(-1) == v.stride(-1) == o.stride(-1) == 1
-    assert dq.stride(-1) == dk.stride(-1) == dv.stride(-1) == 1
-    softmax_scale = softmax_scale or 1.0 / math.sqrt(d)
-    # dq_accum = torch.zeros_like(q, dtype=torch.float32)
-    dq_accum = torch.empty_like(q, dtype=torch.float32)
-    delta = torch.empty_like(lse)
-    # delta = torch.zeros_like(lse)
-
-    BLOCK_HEADDIM = max(triton.next_power_of_2(d), 16)
-    grid = lambda META: (triton.cdiv(seqlen_q, META['BLOCK_M']), batch * nheads)
-    _bwd_preprocess_do_o_dot[grid](  # type: ignore
-        o,
-        do,
-        delta,
-        o.stride(0),
-        o.stride(2),
-        o.stride(1),
-        do.stride(0),
-        do.stride(2),
-        do.stride(1),
-        nheads,
-        seqlen_q,
-        seqlen_q_rounded,
-        d,
-        BLOCK_M=128,
-        BLOCK_HEADDIM=BLOCK_HEADDIM,
-    )
-
-    has_bias = bias is not None
-    bias_type = 'none'
-    if has_bias:
-        assert bias.dtype in [q.dtype, torch.float]
-        assert bias.is_cuda
-        assert bias.dim() == 4
-        assert bias.stride(-1) == 1
-        if bias.shape[2:] == (1, seqlen_k):
-            bias_type = 'vector'
-        elif bias.shape[2:] == (seqlen_q, seqlen_k):
-            bias_type = 'matrix'
-        else:
-            raise RuntimeError('Last 2 dimensions of bias must be (1, seqlen_k)'
-                               ' or (seqlen_q, seqlen_k)')
-        if bias.shape[:2] == (1, nheads):
-            bias = repeat(bias, '1 h ... -> b h ...', b=batch)
-        elif bias.shape[:2] == (batch, 1):
-            bias = repeat(bias, 'b 1 ... -> b h ...', h=nheads)
-        elif bias.shape[:2] == (1, 1):
-            bias = repeat(bias, '1 h ... -> b h ...', b=batch)
-            bias = repeat(bias, 'b 1 ... -> b h ...', h=nheads)
-        assert bias.shape[:2] == (
-            batch, nheads
-        ), f'First 2 dimensions of bias must be broadcastible to (batch, nheads) = ({batch, nheads}). Bias has shape: {bias.shape}'
-    assert bias is not None  # type checking
-    bias_strides = (bias.stride(0), bias.stride(1),
-                    bias.stride(2)) if has_bias else (0, 0, 0)
-
-    # BLOCK_M = 128
-    # BLOCK_N = 64
-    # num_warps = 4
-    grid = lambda META: (triton.cdiv(seqlen_k, META['BLOCK_N'])
-                         if META['SEQUENCE_PARALLEL'] else 1, batch * nheads)
-    _bwd_kernel[grid](  # type: ignore
-        q,
-        k,
-        v,
-        bias,
-        do,
-        dq_accum,
-        dk,
-        dv,
-        lse,
-        delta,
-        softmax_scale,
-        q.stride(0),
-        q.stride(2),
-        q.stride(1),
-        k.stride(0),
-        k.stride(2),
-        k.stride(1),
-        v.stride(0),
-        v.stride(2),
-        v.stride(1),
-        *bias_strides,
-        do.stride(0),
-        do.stride(2),
-        do.stride(1),
-        dq_accum.stride(0),
-        dq_accum.stride(2),
-        dq_accum.stride(1),
-        dk.stride(0),
-        dk.stride(2),
-        dk.stride(1),
-        dv.stride(0),
-        dv.stride(2),
-        dv.stride(1),
-        nheads,
-        seqlen_q,
-        seqlen_k,
-        seqlen_q_rounded,
-        d,
-        seqlen_q // 32,
-        seqlen_k // 32,  # key for triton cache (limit number of compilations)
-        # Can't use kwargs here because triton autotune expects key to be args, not kwargs
-        # IS_CAUSAL=causal, BLOCK_HEADDIM=d,
-        bias_type,
-        causal,
-        BLOCK_HEADDIM,
-        # SEQUENCE_PARALLEL=False,
-        # BLOCK_M=BLOCK_M, BLOCK_N=BLOCK_N,
-        # num_warps=num_warps,
-        # num_stages=1,
-    )
-    dq.copy_(dq_accum)
-
-
-class _FlashAttnQKVPackedFunc(torch.autograd.Function):
-
-    @staticmethod
-    def forward(ctx, qkv, bias=None, causal=False, softmax_scale=None):
-        """Forward pass for packed FlashAttention.
-
-        Args:
-            ctx: autograd context
-            qkv: (batch, seqlen, 3, nheads, headdim)
-            bias: optional, shape broadcastible to (batch, nheads, seqlen, seqlen).
-                For example, ALiBi mask for causal would have shape (1, nheads, 1, seqlen).
-                ALiBi mask for non-causal would have shape (1, nheads, seqlen, seqlen)
-            causal (bool): whether to incorporate causal attention masking
-            softmax_scale (float, optional): scale factor for softmax
-        """
-        # Make sure that the last dimension is contiguous
-        if qkv.stride(-1) != 1:
-            qkv = qkv.contiguous()
-        o, lse, ctx.softmax_scale = _flash_attn_forward(
-            qkv[:, :, 0],
-            qkv[:, :, 1],
-            qkv[:, :, 2],
-            bias=bias,
-            causal=causal,
-            softmax_scale=softmax_scale)
-        ctx.save_for_backward(qkv, o, lse, bias)
-        ctx.causal = causal
-        return o
-
-    @staticmethod
-    def backward(ctx, do):
-        qkv, o, lse, bias = ctx.saved_tensors
-        assert not ctx.needs_input_grad[
-            1], 'FlashAttention does not support bias gradient yet'
-        # Triton's autotune causes the Tensor._version to change, and so Pytorch autograd
-        # does a memcpy. To avoid this we run in inference_mode, which doesn't track the version.
-        with torch.inference_mode():
-            dqkv = torch.empty_like(qkv)
-            _flash_attn_backward(do,
-                                 qkv[:, :, 0],
-                                 qkv[:, :, 1],
-                                 qkv[:, :, 2],
-                                 o,
-                                 lse,
-                                 dqkv[:, :, 0],
-                                 dqkv[:, :, 1],
-                                 dqkv[:, :, 2],
-                                 bias=bias,
-                                 causal=ctx.causal,
-                                 softmax_scale=ctx.softmax_scale)
-        return dqkv, None, None, None
-
-
-flash_attn_qkvpacked_func = _FlashAttnQKVPackedFunc.apply
-
-
-class _FlashAttnFunc(torch.autograd.Function):
-
-    @staticmethod
-    def forward(ctx, q, k, v, bias=None, causal=False, softmax_scale=None):
-        """Forward pass for FlashAttention.
-
-        Args:
-            ctx: autograd context
-            q: (batch_size, seqlen_q, nheads, headdim)
-            k: (batch_size, seqlen_k, nheads, headdim)
-            v: (batch_size, seqlen_k, nheads, headdim)
-            bias: optional, shape broadcastible to (batch, nheads, seqlen_q, seqlen_k).
-                For example, ALiBi mask for causal would have shape (1, nheads, 1, seqlen_k).
-                ALiBi mask for non-causal would have shape (1, nheads, seqlen_q, seqlen_k)
-            causal (bool): whether to incorporate causal attention masking
-            softmax_scale (float, optional): scale factor for softmax
-        """
-        # Make sure that the last dimension is contiguous
-        q, k, v = [
-            x if x.stride(-1) == 1 else x.contiguous() for x in [q, k, v]
-        ]
-        o, lse, ctx.softmax_scale = _flash_attn_forward(
-            q, k, v, bias=bias, causal=causal, softmax_scale=softmax_scale)
-        ctx.save_for_backward(q, k, v, o, lse, bias)
-        ctx.causal = causal
-        return o
-
-    @staticmethod
-    def backward(ctx, do):
-        q, k, v, o, lse, bias = ctx.saved_tensors
-        assert not ctx.needs_input_grad[
-            3], 'FlashAttention does not support bias gradient yet'
-        # Triton's autotune causes the Tensor._version to change, and so Pytorch autograd
-        # does a memcpy. To avoid this we run in inference_mode, which doesn't track the version.
-        with torch.inference_mode():
-            dq = torch.empty_like(q)
-            dk = torch.empty_like(k)
-            dv = torch.empty_like(v)
-            _flash_attn_backward(do,
-                                 q,
-                                 k,
-                                 v,
-                                 o,
-                                 lse,
-                                 dq,
-                                 dk,
-                                 dv,
-                                 bias=bias,
-                                 causal=ctx.causal,
-                                 softmax_scale=ctx.softmax_scale)
-        return dq, dk, dv, None, None, None
-
-
-flash_attn_func = _FlashAttnFunc.apply