megatron.py

r"""
The adaptor to seamlessly enable FastMoE in Megatron-LM v2.0 with at most two
lines of modification.
See `examples/megatron` for usage instructions.
"""
import os
import sys
import math
import random
from collections import OrderedDict
import numpy as np
import torch
import torch.nn as nn
import torch.nn.functional as F

from .transformer import FMoETransformerMLP
from .distributed import DistributedGroupedDataParallel


class _FakeMegatronMLP(nn.Module):
    r"""
    A fake mlp without model parallelism for correctness testing
    """

    def __init__(self, args, _):
        super().__init__()
        self.fc1 = nn.Linear(args.hidden_size, args.hidden_hidden_size)
        self.fc2 = nn.Linear(args.hidden_hidden_size, args.hidden_size)

    def forward(self, x):
        r"""
        Directly use GeLU
        """
        x = self.fc1(x)
        x = F.gelu(x)
        x = self.fc2(x)
        return x, torch.zeros_like(x)


def _megatron_init_method(self, rng, sigma):
    r"""
    Init method based on N(0, sigma).
    Copied from Megatron-LM
    """
    device = self.weight.device
    dtype = self.weight.dtype
    weight = rng.normal(loc=0.0, scale=sigma, size=tuple(self.weight.size()))
    self.weight.data = torch.tensor(weight, dtype=dtype, device=device)

    if self.bias is not None:
        # Always initialize bias to zero.
        with torch.no_grad():
            self.bias.zero_()


def _random_init_weight(self, rng):
    r"""
    Copied from torch.nn.init.kaiming_uniform_
    """
    fan = nn.init._calculate_correct_fan(self.weight[0], "fan_in")
    gain = nn.init.calculate_gain("leaky_relu", math.sqrt(5))
    std = gain / math.sqrt(fan)
    bound = math.sqrt(3.0) * std
    device = self.weight.device
    dtype = self.weight.dtype
    weight = rng.uniform(-bound, bound, size=tuple(self.weight.size()))
    self.weight.data = torch.tensor(weight, dtype=dtype, device=device)

    if self.bias is not None:
        fan_in, _ = nn.init._calculate_fan_in_and_fan_out(self.weight[0])
        bound = 1 / math.sqrt(fan_in)
        bias = rng.uniform(-bound, bound, size=tuple(self.bias.size()))
        self.bias.data = torch.tensor(bias, dtype=dtype, device=device)


class MegatronMLP(FMoETransformerMLP):
    r"""
    Make the FMoETransformerMLP layer that distributes experts across
    communication group `group` to replace the original MLP layer in Megatron.
    """

    def __init__(self, args, group):
        assert (
            args.seq_length * args.micro_batch_size % args.tensor_model_parallel_size
            == 0
        ), "Batch size x sequence length should be multiple of mp size"
        if not args.distributed_experts:
            world_size = 1
        else:
            world_size = args.world_size
        super().__init__(
            args.num_experts,
            top_k=args.top_k,
            d_model=args.hidden_size,
            d_hidden=args.hidden_hidden_size,
            world_size=world_size,
            mp_group=group,
            expert_dp_comm="none" if args.distributed_experts else "dp",
        )
        self.hidden_size = args.hidden_size
        if args.distributed_experts:
            self.rank = args.rank
        else:
            self.rank = 0
        self.sigma = args.init_method_std
        self.num_layers = args.num_layers
        self.reset_parameters()

    def reset_parameters(self):
        r"""
        Initialize the weight as linear layers.
        As megatron is using fixed random seed for some nasty stuff, an
        additional numpy rng is used.
        """
        rng = np.random.default_rng(np.random.randint(2048) + self.rank)
        _megatron_init_method(self.experts.htoh4, rng, self.sigma)
        std = self.sigma / math.sqrt(2.0 * self.num_layers)
        _megatron_init_method(self.experts.h4toh, rng, std)

    def forward(self, inp):
        return (
            super().forward(inp),
            torch.zeros(self.hidden_size, dtype=inp.dtype, device=inp.device),
        )


def fmoefy(
    model,
    num_experts=None,
    distributed_experts=True,
    hidden_hidden_size=None,
    top_k=None,
):
    r"""
    Replace MLP layers in a transformer-based model in Megatron by MoE.
    * `model` should be a standard Megatron model that has
    `model.language_model.transformer.layers` as transformer layers, which is an
    array of transformer blocks that contain an `mlp` member.
    * `distributed_expert` is set to True if different experts are located in
    different workers. Otherwise, the experts on the workers are identical, and
    they are trained in data-parallel mode. This can be useful when testing on
    small models that do not require high training throughput or large parameter
    capacity.
    Note that pipeline parallel is not supported yet. When distributed experts
    are enabled, their communicator should be Megatron's
    tensor_model_parall_comm x data_parallel_comm, which is not created.
    """
    from megatron import get_args
    from megatron import mpu

    args = get_args()
    if num_experts is not None:
        args.num_experts = num_experts
    assert (
        "num_experts" in args
    ), "num_experts should be specified in arguments or fmoefy function"

    if hidden_hidden_size is not None:
        args.hidden_hidden_size = hidden_hidden_size
    elif not hasattr(args, "hidden_hidden_size"):
        args.hidden_hidden_size = args.hidden_size * 4

    if top_k is not None:
        args.top_k = top_k
    elif not hasattr(args, "top_k"):
        args.top_k = 2

    # Set distributed_experts to None to use default setting in args
    if distributed_experts is not None:
        args.distributed_experts = distributed_experts

    for l in model.language_model.transformer.layers:
        l.mlp = MegatronMLP(args, mpu.get_model_parallel_group())
    return model


class DistributedDataParallel(DistributedGroupedDataParallel):
    r"""
    A wrapper that is used to replace the DDP module provided by Megatron, which
    is adapted to enable the sophiscated parallel and reduction strategies in
    Fast MoE.
    """

    def __init__(self, module):
        from megatron import mpu

        super().__init__(
            module,
            mp_group=mpu.get_model_parallel_group(),
            dp_group=mpu.get_data_parallel_group(),
        )

    def state_dict(self, *args, **kwargs):
        r"""
        Keep consitency with Megatron
        """
        return self.module.state_dict(*args, **kwargs)

    def state_dict_for_save_checkpoint(self, *args, **kwargs):
        r"""
        Keep consitency with Megatron
        """
        return self.module.state_dict_for_save_checkpoint(*args, **kwargs)

    def load_state_dict(self, *args, **kwargs):
        r"""
        Keep consitency with Megatron
        """
        return self.module.load_state_dict(*args, **kwargs)


def get_fmoe_checkpoint_name(
    checkpoints_path, iteration, release=False, data_parallel_rank=-1
):
    """A unified checkpoint name, allowing specifying a data parallel rank"""
    from megatron import mpu
    from megatron.checkpointing import get_checkpoint_name

    if data_parallel_rank == -1:
        data_parallel_rank = mpu.get_data_parallel_rank()
    if data_parallel_rank == 0:
        return get_checkpoint_name(checkpoints_path, iteration, release)

    if release:
        directory = "release"
    else:
        directory = "iter_{:07d}".format(iteration)
    # Use both the tensor and pipeline MP rank.
    if mpu.get_pipeline_model_parallel_world_size() == 1:
        return os.path.join(
            checkpoints_path,
            directory,
            "mp_rank_{:02d}_dp_rank_{:04d}".format(
                mpu.get_tensor_model_parallel_rank(), data_parallel_rank
            ),
            "model_optim_rng.pt",
        )
    return os.path.join(
        checkpoints_path,
        directory,
        "mp_rank_{:02d}_{:03d}_dp_rank_{:04d}".format(
            mpu.get_tensor_model_parallel_rank(),
            mpu.get_pipeline_model_parallel_rank(),
            data_parallel_rank,
        ),
        "model_optim_rng.pt",
    )


def save_checkpoint(iteration, model, optimizer, lr_scheduler):
    """Save a model checkpoint with expert parallel """
    # TODO: update patch
    from megatron import get_args
    from megatron import mpu
    from megatron import print_rank_last

    expert_dp_comm = "none"

    if mpu.get_data_parallel_rank() == 0:
        # at dp rank 0, we still follows the native load_checkpoint by megatron
        from megatron.checkpointing import save_checkpoint as save_checkpoint_native

        save_checkpoint_native(iteration, model, optimizer, lr_scheduler)
        return

    args = get_args()

    # Only rank zero of the data parallel writes to the disk.
    if isinstance(model, DistributedDataParallel):
        model = model.module

    print_rank_last(
        "saving checkpoint at iteration {:7d} to {}".format(iteration, args.save)
    )

    # Arguments, iteration, and model.
    state_dict = {}
    state_dict["model"] = model.state_dict_for_save_checkpoint(
        keep_vars=(mpu.get_data_parallel_rank() > 0)
    )

    def extract_expert_param(state_dict, expert_dp_comm="none"):
        state_dict_new = state_dict.__class__()
        for k, v in state_dict.items():
            # megatron uses both dict and OrderedDict in its state_dict
            if isinstance(v, (OrderedDict, dict)):
                v_new = extract_expert_param(v, expert_dp_comm)
                if len(v_new) > 0:
                    state_dict_new[k] = v_new
            elif hasattr(v, "dp_comm") and v.dp_comm == expert_dp_comm:
                state_dict_new[k] = v.detach()
        return state_dict_new

    state_dict["model"] = extract_expert_param(state_dict["model"], expert_dp_comm)

    # Optimizer stuff.
    if not args.no_save_optim:
        if optimizer is not None:
            state_dict["optimizer"] = optimizer.state_dict()
            param_global_idx = 0
            for param_group in optimizer.optimizer.param_groups:
                for param in param_group["params"]:
                    if not (
                        hasattr(param, "dp_comm") and param.dp_comm == expert_dp_comm
                    ):
                        # this parameter is not an expert parameter
                        # thus there is no need to save its state in current rank
                        # since it has been saved by data parallel rank 0
                        if args.fp16:
                            # fp16 optimizer may have empty state due to overflow
                            state_dict["optimizer"]["optimizer"]["state"].pop(
                                param_global_idx, None
                            )
                        else:
                            state_dict["optimizer"]["state"].pop(param_global_idx)
                    param_global_idx += 1
            if args.fp16:
                state_dict["optimizer"]["optimizer"].pop("param_groups")
                # fp32_from_fp16_params in state_dict is not a copy
                # but a reference to optimizer.fp32_from_fp16_params,
                # changing it in state_dict will change
                # optimizer.fp32_from_fp16_params as well
                # thus we create an empty fp32_from_fp16_params in state_dict
                # and only insert expert parameters.
                fp32_from_fp16_params = state_dict["optimizer"]["fp32_from_fp16_params"]
                state_dict["optimizer"]["fp32_from_fp16_params"] = []
                for param_group in fp32_from_fp16_params:
                    param_group_copy = []
                    for param in param_group:
                        param_copy = (
                            param
                            if hasattr(param, "dp_comm")
                            and param.dp_comm == expert_dp_comm
                            else None
                        )
                        param_group_copy.append(param_copy)
                    state_dict["optimizer"]["fp32_from_fp16_params"].append(
                        param_group_copy
                    )
            else:
                state_dict["optimizer"].pop("param_groups")

    # Save.
    checkpoint_name = get_fmoe_checkpoint_name(args.save, iteration)
    from megatron.checkpointing import ensure_directory_exists
    from megatron.checkpointing import get_checkpoint_tracker_filename

    ensure_directory_exists(checkpoint_name)
    torch.save(state_dict, checkpoint_name)

    # Wait so everyone is done (necessary)
    torch.distributed.barrier()
    if torch.distributed.get_rank() == 0:
        print(
            "  successfully saved checkpoint at iteration {:7d} to {}".format(
                iteration, args.save
            ),
            flush=True,
        )
    # And update the latest iteration
    if torch.distributed.get_rank() == 0:
        tracker_filename = get_checkpoint_tracker_filename(args.save)
        with open(tracker_filename, "w") as f:
            f.write(str(iteration))
    # Wait so everyone is done (not necessary)
    torch.distributed.barrier()


def merge_state_dict(state_dict_rank0, state_dict_local, fp16):
    """merge two state dicts, one from data parallel rank 0,
    another only contains expert states"""
    from megatron import print_rank_last

    def merge_model(state_dict_rank0, state_dict_local):
        for k, v in state_dict_local.items():
            # megatron uses both dict and OrderedDict in its state_dict
            if isinstance(v, (OrderedDict, dict)):
                merge_model(state_dict_rank0[k], v)
            else:
                state_dict_rank0[k] = v

    merge_model(state_dict_rank0["model"], state_dict_local["model"])

    optimizer_rank0 = (
        state_dict_rank0["optimizer"]["optimizer"]
        if fp16
        else state_dict_rank0["optimizer"]
    )
    optimizer_local = (
        state_dict_local["optimizer"]["optimizer"]
        if fp16
        else state_dict_local["optimizer"]
    )

    for k, v in optimizer_local["state"].items():
        optimizer_rank0["state"][k] = v

    if fp16:
        for group_idx, param_group in enumerate(
            state_dict_local["optimizer"]["fp32_from_fp16_params"]
        ):
            for param_in_group_idx, param in enumerate(param_group):
                if param is not None:
                    state_dict_rank0["optimizer"]["fp32_from_fp16_params"][group_idx][
                        param_in_group_idx
                    ] = param

    return state_dict_rank0


def load_checkpoint(model, optimizer, lr_scheduler, load_arg="load"):
    """Load a model checkpoint and return the iteration."""

    from megatron import get_args
    from megatron import mpu
    from megatron import print_rank_last
    from megatron.checkpointing import get_checkpoint_tracker_filename
    from megatron.checkpointing import set_checkpoint_version
    from megatron.checkpointing import check_checkpoint_args
    from megatron.checkpointing import update_num_microbatches

    if mpu.get_data_parallel_rank() == 0:
        # at dp rank 0, we still follow the native load_checkpoint by megatron
        from megatron.checkpointing import load_checkpoint as load_checkpoint_native

        return load_checkpoint_native(model, optimizer, lr_scheduler, load_arg)

    args = get_args()
    load_dir = getattr(args, load_arg)

    if isinstance(model, DistributedDataParallel):
        model = model.module
    # Read the tracker file and set the iteration.
    tracker_filename = get_checkpoint_tracker_filename(load_dir)

    # If no tracker file, return iretation zero.
    if not os.path.isfile(tracker_filename):
        print_rank_last(
            "WARNING: could not find the metadata file {} ".format(tracker_filename)
        )
        print_rank_last(
            "    will not load any checkpoints and will start from " "random"
        )
        return 0

    # Otherwise, read the tracker file and either set the iteration or
    # mark it as a release checkpoint.
    iteration = 0
    release = False
    with open(tracker_filename, "r") as f:
        metastring = f.read().strip()
        try:
            iteration = int(metastring)
        except ValueError:
            release = metastring == "release"
            if not release:
                print_rank_last(
                    "ERROR: Invalid metadata file {}. Exiting".format(tracker_filename)
                )
                sys.exit()

    assert iteration > 0 or release, "error parsing metadata file {}".format(
        tracker_filename
    )

    # Checkpoint.
    checkpoint_name_rank0 = get_fmoe_checkpoint_name(load_dir, iteration, release, 0)
    checkpoint_name_local = get_fmoe_checkpoint_name(
        load_dir, iteration, release, mpu.get_data_parallel_rank()
    )
    print_rank_last(
        " loading checkpoint at rank 0 from {} and rank {} from {} at iteration {}, will merge them later".format(
            checkpoint_name_rank0,
            mpu.get_data_parallel_rank(),
            checkpoint_name_local,
            iteration,
        )
    )

    # Load the checkpoint.
    def load_state_dict(checkpoint_name):
        try:
            state_dict = torch.load(checkpoint_name, map_location="cpu")
        except ModuleNotFoundError:
            from megatron.fp16_deprecated import loss_scaler

            # For backward compatibility.
            print_rank_last(" > deserializing using the old code structure ...")
            sys.modules["fp16.loss_scaler"] = sys.modules[
                "megatron.fp16_deprecated.loss_scaler"
            ]
            sys.modules["megatron.fp16.loss_scaler"] = sys.modules[
                "megatron.fp16_deprecated.loss_scaler"
            ]
            state_dict = torch.load(checkpoint_name, map_location="cpu")
            sys.modules.pop("fp16.loss_scaler", None)
            sys.modules.pop("megatron.fp16.loss_scaler", None)
        except BaseException:
            print_rank_last("could not load the checkpoint")
            sys.exit()
        return state_dict

    state_dict_rank0 = load_state_dict(checkpoint_name_rank0)
    state_dict_local = load_state_dict(checkpoint_name_local)

    state_dict = merge_state_dict(state_dict_rank0, state_dict_local, args.fp16)

    # set checkpoint version
    set_checkpoint_version(state_dict.get("checkpoint_version", 0))

    # Set iteration.
    if args.finetune or release:
        iteration = 0
    else:
        try:
            iteration = state_dict["iteration"]
        except KeyError:
            try:  # Backward compatible with older checkpoints
                iteration = state_dict["total_iters"]
            except KeyError:
                print_rank_last(
                    "A metadata file exists but unable to load "
                    "iteration from checkpoint {}, exiting".format(
                        checkpoint_name_local
                    )
                )
                sys.exit()

    # Check arguments.
    assert args.consumed_train_samples == 0
    assert args.consumed_valid_samples == 0
    if "args" in state_dict:
        checkpoint_args = state_dict["args"]
        check_checkpoint_args(checkpoint_args)
        args.consumed_train_samples = getattr(
            checkpoint_args, "consumed_train_samples", 0
        )
        update_num_microbatches(consumed_samples=args.consumed_train_samples)
        args.consumed_valid_samples = getattr(
            checkpoint_args, "consumed_valid_samples", 0
        )
    else:
        print_rank_last("could not find arguments in the checkpoint ...")

    # Model.
    model.load_state_dict(state_dict["model"])

    # Optimizer.
    if not release and not args.finetune and not args.no_load_optim:
        try:
            if optimizer is not None:
                optimizer.load_state_dict(state_dict["optimizer"])
            if lr_scheduler is not None:
                lr_scheduler.load_state_dict(state_dict["lr_scheduler"])
        except KeyError:
            print_rank_last(
                "Unable to load optimizer from checkpoint {}. "
                "Specify --no-load-optim or --finetune to prevent "
                "attempting to load the optimizer state, "
                "exiting ...".format(checkpoint_name_local)
            )
            sys.exit()

    # rng states.
    if not release and not args.finetune and not args.no_load_rng:
        try:
            random.setstate(state_dict["random_rng_state"])
            np.random.set_state(state_dict["np_rng_state"])
            torch.set_rng_state(state_dict["torch_rng_state"])
            torch.cuda.set_rng_state(state_dict["cuda_rng_state"])
            mpu.get_cuda_rng_tracker().set_states(state_dict["rng_tracker_states"])
        except KeyError:
            print_rank_last(
                "Unable to load optimizer from checkpoint {}. "
                "Specify --no-load-rng or --finetune to prevent "
                "attempting to load the optimizer state, "
                "exiting ...".format(checkpoint_name_local)
            )
            sys.exit()

    torch.distributed.barrier()
    print_rank_last(
        "  successfully loaded checkpoint (with expert parametes updated) from {} at iteration {}".format(
            args.load, iteration
        )
    )

    return iteration