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
from .balance import update_balance_profile, reset_balance_profile
from .utils import get_torch_default_comm


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.from_numpy(weight).to(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.from_numpy(weight).to(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.from_numpy(bias).to(dtype=dtype, device=device)


balance_dict = {}
num_layers = 0


def reset_gate_hook():
    from megatron import get_args

    global balance_dict, num_layers
    reset_balance_profile(balance_dict, num_layers, get_args().balance_strategy)


def get_balance_profile():
    global balance_dict
    return balance_dict


def generate_megatron_gate_hook(layer_idx, num_expert_global):
    from megatron import get_args

    balance_strategy = get_args().balance_strategy

    def megatron_gate_hook(gate_top_k_idx, gate_score_top_k, gate_state_dict):
        global balance_dict
        update_balance_profile(
            balance_dict,
            gate_top_k_idx,
            gate_score_top_k,
            gate_state_dict,
            layer_idx,
            num_expert_global,
            balance_strategy,
        )

    return megatron_gate_hook


def add_fmoe_args(parser):
    group = parser.add_argument_group(title="fastmoe")

    group.add_argument("--fmoefy", action="store_true")
    group.add_argument("--num-experts", type=int, default=None)
    group.add_argument("--top-k", type=int, default=2)
    group.add_argument("--balance-loss-weight", type=float, default=1)
    group.add_argument("--balance-strategy", type=str, default=None)

    return parser


def add_balance_log(writer, iteration):
    from megatron import is_last_rank

    balance_dict_tensor = torch.vstack(
        [torch.tensor(item, device=item[0].device) for item in balance_dict.values()]
    ).detach()
    world_group = get_torch_default_comm()
    world_size = torch.distributed.get_world_size(group=world_group)
    torch.distributed.all_reduce(balance_dict_tensor, group=world_group)
    balance_dict_tensor /= world_size

    if writer and is_last_rank():
        for idx, metric_name in enumerate(balance_dict):
            for layer_id, val in enumerate(balance_dict_tensor[idx]):
                writer.add_scalar(
                    f"balance-{metric_name}/layer-{layer_id}", val.item(), iteration
                )
            writer.add_scalar(
                f"balance-{metric_name}/all",
                balance_dict_tensor[idx].mean().item(),
                iteration,
            )

    reset_gate_hook()


def patch_forward_step(forward_step_func):
    r"""
    Patch model's forward_step_func to support balance loss
    """

    from megatron.mpu import is_pipeline_last_stage
    from megatron import get_args

    if not get_args().balance_strategy:
        return forward_step_func

    def forward_step_with_balance_loss(data_iterator, model, input_tensor):
        args = get_args()
        output = forward_step_func(data_iterator, model, input_tensor)

        if is_pipeline_last_stage():
            loss_name = args.balance_strategy + "_loss"

            (loss, state_dict), bal_loss = (
                output,
                (
                    torch.tensor(
                        balance_dict[loss_name],
                        device=balance_dict[loss_name][0].device,
                    ).mean()
                    * args.balance_loss_weight
                ).float(),
            )

            # avarage across world group
            world_group = get_torch_default_comm()
            world_size = torch.distributed.get_world_size(group=world_group)
            averaged_bal_loss = bal_loss.clone().detach()
            torch.distributed.all_reduce(averaged_bal_loss, group=world_group)
            averaged_bal_loss /= world_size

            loss += bal_loss
            state_dict[loss_name] = averaged_bal_loss

            return loss, state_dict
        else:
            return output

    return forward_step_with_balance_loss


def patch_model_provider(model_provider):
    from megatron import get_args

    def fmoefied_model_provider():
        args = get_args()
        return fmoefy(
            model_provider(),
            num_experts=args.num_experts,
            hidden_hidden_size=4 * args.hidden_size // args.top_k,
            top_k=args.top_k,
        )

    return fmoefied_model_provider


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, layer_idx):
        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
        gate = None
        if not args.balance_strategy or args.balance_strategy == "gshard":
            from .gates import NaiveGate

            gate = NaiveGate
        elif args.balance_strategy == "noisy":
            from .gates import NoisyGate

            gate = NoisyGate
        else:
            assert False, "Undefined balance strategy {}" % (args.balance_strategy)
        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",
            gate_hook=generate_megatron_gate_hook(
                layer_idx, args.num_experts * world_size
            ),
            gate=gate,
        )
        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 idx, l in enumerate(model.language_model.transformer.layers):
        l.mlp = MegatronMLP(args, mpu.get_model_parallel_group(), idx)

    # initialize gate hook
    global num_layers, balance_dict
    num_layers = len(model.language_model.transformer.layers)
    reset_gate_hook()

    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, expert_dp_comm='none'):
    """Save a model checkpoint with expert parallel """
    # TODO: update patch
    from megatron import get_args
    from megatron import mpu

    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

    if torch.distributed.get_rank() == 0:
        print('saving checkpoint at iteration {:7d} to {}'.format(
            iteration, args.save), flush=True)

    # 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()
            index = 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(index, None)
                        else:
                            state_dict['optimizer']['state'].pop(index)
                    index += 1
            if args.fp16:
                state_dict['optimizer']['optimizer'].pop('param_groups')
            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)):
                print_rank_last("[merge model] go recursively to {}".format(k))
                merge_model(state_dict_rank0[k], v)
            else:
                before = state_dict_rank0[k].sum().item()
                state_dict_rank0[k] = v
                after = state_dict_rank0[k].sum().item()
                print_rank_last("[merge model] copy parameter {}, \
                    before.sum={:7f}, after.sum={:7f}".format(k, before, after))
    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():
        before = {kk: vv.sum().item() \
            for kk, vv in optimizer_rank0['state'][k].items()}
        optimizer_rank0['state'][k] = v
        after = {kk: vv.sum().item() \
            for kk, vv in optimizer_rank0['state'][k].items()}
        print_rank_last("[merge optimizer] copy {}, \
               before.sum={}, after.sum={}".format(k, str(before), str(after)))
    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, set_checkpoint_version, check_checkpoint_args, 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