flash-attention/hopper/generate_kernels.py

# Copied from Driss Guessous's PR in PyTorch: https://github.com/pytorch/pytorch/pull/105602

# This file is run to generate the kernel instantiations for the flash_attn kernels
# They are written to several files in order to speed up compilation

import argparse
import itertools
from collections import namedtuple
from dataclasses import dataclass
from pathlib import Path
from typing import List, Optional

KERNEL_BATCH = namedtuple("Kernel", ["template", "filename"])

DTYPE_MAP = {
    "fp16": "cutlass::half_t",
    "bf16": "cutlass::bfloat16_t",
    "e4m3": "cutlass::float_e4m3_t",
}

DTYPE_MAP_BWD = {
    "fp16": "cutlass::half_t",
    "bf16": "cutlass::bfloat16_t",
}

SM = [90]  # Sm kernels support up to
HEAD_DIMENSIONS = [64, 96, 128, 192, 256]
PAGEDKV = [False, True]
SPLIT = [False, True]
SOFTCAP = [False, True]
PACKGQA = [False, True]
KERNEL_IMPL_TEMPLATE_FWD = """#include "flash_fwd_launch_template.h"

#ifndef FLASHATTENTION_DISABLE_HDIM{HEAD_DIM}
template void run_mha_fwd_<{DTYPE}, {HEAD_DIM}, {SPLIT}, {PAGEDKV}, {SOFTCAP}, {PACKGQA}>(Flash_fwd_params &params, cudaStream_t stream);
#endif
"""

KERNEL_IMPL_TEMPLATE_BWD = """#include "flash_bwd_launch_template.h"

#ifndef FLASHATTENTION_DISABLE_HDIM{HEAD_DIM}
template<>
void run_mha_bwd_<{DTYPE}, {HEAD_DIM}>(Flash_bwd_params &params, cudaStream_t stream) {{
    run_mha_bwd_hdim{HEAD_DIM}<{DTYPE}>(params, stream);
}}
#endif
"""


@dataclass
class Kernel:
    sm: int
    dtype: str
    head_dim: int
    split: bool
    paged_kv: bool
    softcap: bool
    packgqa: bool
    direction: str

    @property
    def template(self) -> str:
        if self.direction == "fwd":
            return KERNEL_IMPL_TEMPLATE_FWD.format(
                DTYPE=DTYPE_MAP[self.dtype], HEAD_DIM=self.head_dim,
                SPLIT=str(self.split).lower(), PAGEDKV=str(self.paged_kv).lower(),
                SOFTCAP=str(self.softcap).lower(), PACKGQA=str(self.packgqa).lower()
            )
        elif self.direction == "bwd":
            return KERNEL_IMPL_TEMPLATE_BWD.format(
                DTYPE=DTYPE_MAP[self.dtype], HEAD_DIM=self.head_dim
            )

    @property
    def filename(self) -> str:
        return f"flash_{self.direction}_hdim{self.head_dim}_{self.dtype}{'_paged' if self.paged_kv else ''}{'_split' if self.split else ''}{'_softcap' if self.softcap else ''}{'_packgqa' if self.packgqa else ''}_sm{self.sm}.cu"


def get_all_kernels() -> List[Kernel]:
    for dtype, head_dim, split, paged_kv, softcap, packgqa, sm in itertools.product(DTYPE_MAP.keys(), HEAD_DIMENSIONS, SPLIT, PAGEDKV, SOFTCAP, PACKGQA, SM):
        yield Kernel(sm=sm, dtype=dtype, head_dim=head_dim, split=split, paged_kv=paged_kv, softcap=softcap, packgqa=packgqa, direction="fwd")
    for dtype, head_dim, sm in itertools.product(DTYPE_MAP_BWD.keys(), HEAD_DIMENSIONS, SM):
        yield Kernel(sm=sm, dtype=dtype, head_dim=head_dim, split=False, paged_kv=False, softcap=False, packgqa=False, direction="bwd")


def batch_hdim(kernels_all) -> List[KERNEL_BATCH]:
    for dtype, split, paged_kv, softcap, packgqa, sm in itertools.product(DTYPE_MAP.keys(), SPLIT, PAGEDKV, SOFTCAP, PACKGQA, SM):
        kernels = [k for k in kernels_all if k.direction == "fwd" and k.dtype == dtype and k.split == split and k.paged_kv == paged_kv and k.softcap == softcap and k.packgqa == packgqa]
        assert len(kernels) > 0
        filename = f"flash_fwd_hdimall_{dtype}{'_paged' if paged_kv else ''}{'_split' if split else ''}{'_softcap' if softcap else ''}{'_packgqa' if packgqa else ''}_sm{sm}.cu"
        template = "\n".join([f"#include \"{k.filename}\"" for k in kernels])
        yield KERNEL_BATCH(template, filename)


def write_kernel(kernel: Kernel, autogen_dir: Path) -> None:
    prelude = """// Copyright (c) 2024, Jay Shah, Ganesh Bikshandi, Ying Zhang, Vijay Thakkar, Pradeep Ramani, Tri Dao.
// Splitting the different template instantiations to different files to speed up compilation.
// This file is auto-generated. See "generate_kernels.py"\n
"""
    (autogen_dir / kernel.filename).write_text(prelude + kernel.template)


def main(output_dir: Optional[str]) -> None:
    output_dir = Path(output_dir) if output_dir is not None else Path(__file__).parent
    output_dir.mkdir(parents=True, exist_ok=True)
    kernels_all = list(get_all_kernels())
    for kernel in kernels_all:
        write_kernel(kernel, output_dir)
    for kernel in batch_hdim(kernels_all):
        write_kernel(kernel, output_dir)


if __name__ == "__main__":
    parser = argparse.ArgumentParser(
        prog="generate_kernels",
        description="Generate the flash_attention kernels template instantiations",
    )
    # Set an optional output directory
    parser.add_argument(
        "-o",
        "--output_dir",
        default="instantiations",
        required=False,
        help="Where to generate the kernels "
        " will default to the current directory ",
    )
    args = parser.parse_args()
    main(args.output_dir)