jit.py

# Copyright (c) 2022, NVIDIA CORPORATION & AFFILIATES. All rights reserved.
#
# See LICENSE for license information.

"""NVFuser functions and JIT utilities"""
from typing import Callable, Tuple
import torch


def set_jit_fusion_options() -> None:
    """Set PyTorch JIT layer fusion options."""
    # flags required to enable jit fusion kernels
    TORCH_MAJOR = int(torch.__version__.split(".")[0])
    TORCH_MINOR = int(torch.__version__.split(".")[1])
    if (TORCH_MAJOR > 1) or (TORCH_MAJOR == 1 and TORCH_MINOR >= 10):
        # nvfuser
        torch._C._jit_set_profiling_executor(True)
        torch._C._jit_set_profiling_mode(True)
        torch._C._jit_override_can_fuse_on_cpu(False)
        torch._C._jit_override_can_fuse_on_gpu(False)
        torch._C._jit_set_texpr_fuser_enabled(False)
        torch._C._jit_set_nvfuser_enabled(True)
        torch._C._debug_set_autodiff_subgraph_inlining(False)
    else:
        # legacy pytorch fuser
        torch._C._jit_set_profiling_mode(False)
        torch._C._jit_set_profiling_executor(False)
        torch._C._jit_override_can_fuse_on_cpu(True)
        torch._C._jit_override_can_fuse_on_gpu(True)


@torch.jit.script
def bias_gelu_fused_(inp: torch.Tensor, bias: torch.Tensor) -> torch.Tensor:
    """Bias-GeLU fused"""
    x = inp + bias
    return x * 0.5 * (1.0 + torch.tanh(0.79788456 * x * (1 + 0.044715 * x * x)))


# gradient of tanh approximation of gelu
# gradient of actual gelu is:
# 0.5 * (1. + torch.erf(x * 0.70710678)) + 0.3989423 * x * torch.exp(-0.5 * x * x)
@torch.jit.script
def bgrad_dgelu_fused_(
    grad_output: torch.Tensor, inp: torch.Tensor, bias: torch.Tensor
) -> Tuple[torch.Tensor, torch.Tensor]:
    """Bgrad-Dgelu fused"""
    x = inp + bias
    tanh_out = torch.tanh(0.79788456 * x * (1 + 0.044715 * x * x))
    # sqrt(2/pi) * 3 * 0.044715 -> 0.1070322243
    ff = 0.5 * x * (
        (1 - tanh_out * tanh_out) * (0.79788456 + 0.1070322243 * x * x)
    ) + 0.5 * (1 + tanh_out)
    dgelu = ff * grad_output
    bgrad = dgelu.sum(dim=0)
    return bgrad, dgelu


def bias_gelu_fused(inp: torch.Tensor, bias: torch.Tensor) -> torch.Tensor:
    """Disable native AMP for bias_gelu_fused_"""
    with torch.cuda.amp.autocast(enabled=False):
        return bias_gelu_fused_(inp, bias)


def bgrad_dgelu_fused(
    grad_output: torch.Tensor, inp: torch.Tensor, bias: torch.Tensor
) -> Tuple[torch.Tensor, torch.Tensor]:
    """Disable native AMP for `bgrad_dgelu_fused_`"""
    with torch.cuda.amp.autocast(enabled=False):
        return bgrad_dgelu_fused_(grad_output, inp, bias)


def bias_dropout_add(
    x: torch.Tensor,
    bias: torch.Tensor,
    residual: torch.Tensor,
    prob: float,
    training: bool,
) -> torch.Tensor:
    """dropout(inp + bias) + residual"""
    out = torch.nn.functional.dropout(x + bias, p=prob, training=training)
    out = residual + out
    return out


def get_bias_dropout_add(training: bool) -> Callable:
    """bias_dropout_add based on training or not"""

    def _bias_dropout_add(x, bias, residual, prob):
        return bias_dropout_add(x, bias, residual, prob, training)

    return _bias_dropout_add


@torch.jit.script
def bias_dropout_add_fused_train_(
    x: torch.Tensor, bias: torch.Tensor, residual: torch.Tensor, prob: float
) -> torch.Tensor:
    """Jit fused bias_dropout_add for training"""
    return bias_dropout_add(x, bias, residual, prob, True)


def bias_dropout_add_fused_train(
    x: torch.Tensor, bias: torch.Tensor, residual: torch.Tensor, prob: float
) -> torch.Tensor:
    """Disable native AMP and enable grad for BDA"""
    with torch.enable_grad():
        with torch.cuda.amp.autocast(enabled=False):
            return bias_dropout_add_fused_train_(x, bias, residual, prob)


@torch.jit.script
def bias_dropout_add_fused_inference_(
    x: torch.Tensor, bias: torch.Tensor, residual: torch.Tensor, prob: float
) -> torch.Tensor:
    """Jit fused bias_dropout_add for inference"""
    return bias_dropout_add(x, bias, residual, prob, False)


def bias_dropout_add_fused_inference(
    x: torch.Tensor, bias: torch.Tensor, residual: torch.Tensor, prob: float
) -> torch.Tensor:
    """Disable native AMP for BDA"""
    with torch.cuda.amp.autocast(enabled=False):
        return bias_dropout_add_fused_inference_(x, bias, residual, prob)


def warmup_jit_bias_dropout_add(
    hidden_size: int, dtype: torch.dtype, seq_length: int, micro_batch_size: int
) -> None:
    """Compilie BDA JIT function before the main training steps"""
    # Warmup fused bias+dropout+add
    inp = torch.rand(
        (seq_length, micro_batch_size, hidden_size), dtype=dtype, device="cuda"
    )
    residual = torch.rand(
        (seq_length, micro_batch_size, hidden_size), dtype=dtype, device="cuda"
    )
    bias = torch.rand((hidden_size), dtype=dtype, device="cuda")
    dropout_rate = 0.1
    # Warmup JIT fusions with the input grad_enable state of both forward
    # prop and recomputation
    for input_grad, bias_grad, residual_grad in zip(
        [False, True], [True, True], [True, True]
    ):
        inp.requires_grad = input_grad
        bias.requires_grad = bias_grad
        residual.requires_grad = residual_grad
        for _ in range(5):
            output = bias_dropout_add_fused_train(inp, bias, residual, dropout_rate)
    del bias, inp, residual, output
    torch.cuda.empty_cache()


def warmup_jit_bias_dropout_add_all_dtypes(
    hidden_size: int, seq_length: int, micro_batch_size: int
) -> None:
    """Call `warmup_jit_bias_dropout_add` for all training dtypes"""
    for dtype in [torch.float32, torch.bfloat16, torch.float16]:
        warmup_jit_bias_dropout_add(hidden_size, dtype, seq_length, micro_batch_size)


def warmup_jit_bias_gelu(
    ffn_hidden_size_per_partition: int,
    dtype: torch.dtype,
    seq_length: int,
    micro_batch_size: int,
) -> None:
    """Compilie bias-gelu JIT function before the main training steps"""
    # Warmup fused bias+gelu
    bias = torch.rand(ffn_hidden_size_per_partition, dtype=dtype, device="cuda")
    inp = torch.rand(
        (seq_length, micro_batch_size, ffn_hidden_size_per_partition),
        dtype=dtype,
        device="cuda",
    )
    # Warmup JIT fusions with the input grad_enable state of both forward
    # prop and recomputation
    for bias_grad, input_grad in zip([True, True], [False, True]):
        bias.requires_grad, inp.requires_grad = bias_grad, input_grad
        for _ in range(5):
            output = bias_gelu_fused(inp, bias)
    del bias, inp, output


def warmup_jit_bias_gelu_all_dtypes(
    ffn_hidden_size: int, seq_length: int, micro_batch_size: int
) -> None:
    """Call `warmup_jit_bias_gelu` for all training dtypes"""
    for dtype in [torch.float32, torch.bfloat16, torch.float16]:
        warmup_jit_bias_gelu(ffn_hidden_size, dtype, seq_length, micro_batch_size)