initialize.py

# Copyright (c) 2022, NVIDIA CORPORATION. All rights reserved.


"""Model and data parallel groups."""

import torch

from .utils import ensure_divisibility


# Intra-layer model parallel group that the current rank belongs to.
_TENSOR_MODEL_PARALLEL_GROUP = None
# Inter-layer model parallel group that the current rank belongs to.
_PIPELINE_MODEL_PARALLEL_GROUP = None
# Model parallel group (both intra- and pipeline) that the current rank belongs to.
_MODEL_PARALLEL_GROUP = None
# Embedding group.
_EMBEDDING_GROUP = None
# Position embedding group.
_POSITION_EMBEDDING_GROUP = None
# Data parallel group that the current rank belongs to.
_DATA_PARALLEL_GROUP = None

_VIRTUAL_PIPELINE_MODEL_PARALLEL_RANK = None
_VIRTUAL_PIPELINE_MODEL_PARALLEL_WORLD_SIZE = None
_PIPELINE_MODEL_PARALLEL_SPLIT_RANK = None

# These values enable us to change the mpu sizes on the fly.
_MPU_TENSOR_MODEL_PARALLEL_WORLD_SIZE = None
_MPU_PIPELINE_MODEL_PARALLEL_WORLD_SIZE = None
_MPU_TENSOR_MODEL_PARALLEL_RANK = None
_MPU_PIPELINE_MODEL_PARALLEL_RANK = None

# A list of ranks that have a copy of the embedding.
_EMBEDDING_GLOBAL_RANKS = None

# A list of ranks that have a copy of the position embedding.
_POSITION_EMBEDDING_GLOBAL_RANKS = None

# A list of global ranks for each pipeline group to ease calculation of the source
# rank when broadcasting from the first or last pipeline stage.
_PIPELINE_GLOBAL_RANKS = None

# A list of global ranks for each data parallel group to ease calculation of the source
# rank when broadcasting weights from src to all other data parallel ranks
_DATA_PARALLEL_GLOBAL_RANKS = None



def is_unitialized():
    """Useful for code segments that may be accessed with or without mpu initialization"""
    return _DATA_PARALLEL_GROUP is None


def initialize_model_parallel(tensor_model_parallel_size_=1,
                              pipeline_model_parallel_size_=1,
                              virtual_pipeline_model_parallel_size_=None,
                              pipeline_model_parallel_split_rank_=None):
    """
    Initialize model data parallel groups.

    Arguments:
        tensor_model_parallel_size: number of GPUs used for tensor model parallelism.
        pipeline_model_parallel_size: number of GPUs used for pipeline model parallelism.
        virtual_pipeline_model_parallel_size: number of virtual stages (interleaved
                                              pipeline).
        pipeline_model_parallel_split_rank: for models with both encoder and decoder,
                                            rank in pipeline with split point.


    Let's say we have a total of 16 GPUs denoted by g0 ... g15 and we
    use 2 GPUs to parallelize the model tensor, and 4 GPUs to parallelize
    the model pipeline. The present function will
    create 8 tensor model-parallel groups, 4 pipeline model-parallel groups
    and 8 data-parallel groups as:
        8 data_parallel groups:
            [g0, g2], [g1, g3], [g4, g6], [g5, g7], [g8, g10], [g9, g11], [g12, g14], [g13, g15]
        8 tensor model-parallel groups:
            [g0, g1], [g2, g3], [g4, g5], [g6, g7], [g8, g9], [g10, g11], [g12, g13], [g14, g15]
        4 pipeline model-parallel groups:
            [g0, g4, g8, g12], [g1, g5, g9, g13], [g2, g6, g10, g14], [g3, g7, g11, g15]
    Note that for efficiency, the caller should make sure adjacent ranks
    are on the same DGX box. For example if we are using 2 DGX-1 boxes
    with a total of 16 GPUs, rank 0 to 7 belong to the first box and
    ranks 8 to 15 belong to the second box.
    """
    if torch.distributed.get_rank() == 0:
        print('> initializing tensor model parallel with size {}'.format(
            tensor_model_parallel_size_))
        print('> initializing pipeline model parallel with size {}'.format(
            pipeline_model_parallel_size_))
    # Get world size and rank. Ensure some consistencies.
    assert torch.distributed.is_initialized()
    world_size = torch.distributed.get_world_size()
    tensor_model_parallel_size = min(tensor_model_parallel_size_, world_size)
    pipeline_model_parallel_size = min(pipeline_model_parallel_size_, world_size)
    ensure_divisibility(world_size,
                        tensor_model_parallel_size * pipeline_model_parallel_size)
    data_parallel_size = world_size // (tensor_model_parallel_size *
                                        pipeline_model_parallel_size)

    num_tensor_model_parallel_groups = world_size // tensor_model_parallel_size
    num_pipeline_model_parallel_groups = world_size // pipeline_model_parallel_size
    num_data_parallel_groups = world_size // data_parallel_size

    if virtual_pipeline_model_parallel_size_ is not None:
        global _VIRTUAL_PIPELINE_MODEL_PARALLEL_RANK
        global _VIRTUAL_PIPELINE_MODEL_PARALLEL_WORLD_SIZE
        _VIRTUAL_PIPELINE_MODEL_PARALLEL_RANK = 0
        _VIRTUAL_PIPELINE_MODEL_PARALLEL_WORLD_SIZE = virtual_pipeline_model_parallel_size_

    if pipeline_model_parallel_split_rank_ is not None:
        global _PIPELINE_MODEL_PARALLEL_SPLIT_RANK
        _PIPELINE_MODEL_PARALLEL_SPLIT_RANK = pipeline_model_parallel_split_rank_

    rank = torch.distributed.get_rank()

    # Build the data-parallel groups.
    global _DATA_PARALLEL_GROUP
    global _DATA_PARALLEL_GLOBAL_RANKS
    assert _DATA_PARALLEL_GROUP is None, \
        'data parallel group is already initialized'
    all_data_parallel_group_ranks = []
    for i in range(pipeline_model_parallel_size):
        start_rank = i * num_pipeline_model_parallel_groups
        end_rank = (i + 1) * num_pipeline_model_parallel_groups
        for j in range(tensor_model_parallel_size):
            ranks = range(start_rank + j, end_rank,
                          tensor_model_parallel_size)
            all_data_parallel_group_ranks.append(list(ranks))
            group = torch.distributed.new_group(ranks)
            if rank in ranks:
                _DATA_PARALLEL_GROUP = group
                _DATA_PARALLEL_GLOBAL_RANKS = ranks

    # Build the model-parallel groups.
    global _MODEL_PARALLEL_GROUP
    assert _MODEL_PARALLEL_GROUP is None, \
        'model parallel group is already initialized'
    for i in range(data_parallel_size):
        ranks = [data_parallel_group_ranks[i]
                 for data_parallel_group_ranks in all_data_parallel_group_ranks]
        group = torch.distributed.new_group(ranks)
        if rank in ranks:
            _MODEL_PARALLEL_GROUP = group

    # Build the tensor model-parallel groups.
    global _TENSOR_MODEL_PARALLEL_GROUP
    assert _TENSOR_MODEL_PARALLEL_GROUP is None, \
        'tensor model parallel group is already initialized'
    for i in range(num_tensor_model_parallel_groups):
        ranks = range(i * tensor_model_parallel_size,
                      (i + 1) * tensor_model_parallel_size)
        group = torch.distributed.new_group(ranks)
        if rank in ranks:
            _TENSOR_MODEL_PARALLEL_GROUP = group

    # Build the pipeline model-parallel groups and embedding groups
    # (first and last rank in each pipeline model-parallel group).
    global _PIPELINE_MODEL_PARALLEL_GROUP
    global _PIPELINE_GLOBAL_RANKS
    assert _PIPELINE_MODEL_PARALLEL_GROUP is None, \
        'pipeline model parallel group is already initialized'
    global _EMBEDDING_GROUP
    global _EMBEDDING_GLOBAL_RANKS
    assert _EMBEDDING_GROUP is None, \
        'embedding group is already initialized'
    global _POSITION_EMBEDDING_GROUP
    global _POSITION_EMBEDDING_GLOBAL_RANKS
    assert _POSITION_EMBEDDING_GROUP is None, \
        'position embedding group is already initialized'
    for i in range(num_pipeline_model_parallel_groups):
        ranks = range(i, world_size,
                      num_pipeline_model_parallel_groups)
        group = torch.distributed.new_group(ranks)
        if rank in ranks:
            _PIPELINE_MODEL_PARALLEL_GROUP = group
            _PIPELINE_GLOBAL_RANKS = ranks
        # Setup embedding group (to exchange gradients between
        # first and last stages).
        if len(ranks) > 1:
            embedding_ranks = [ranks[0], ranks[-1]]
            position_embedding_ranks = [ranks[0]]
            if pipeline_model_parallel_split_rank_ is not None:
                if ranks[pipeline_model_parallel_split_rank_] not in embedding_ranks:
                    embedding_ranks = [ranks[0],
                                       ranks[pipeline_model_parallel_split_rank_],
                                       ranks[-1]]
                if ranks[pipeline_model_parallel_split_rank_] not in position_embedding_ranks:
                    position_embedding_ranks = [ranks[0],
                                       ranks[pipeline_model_parallel_split_rank_]]
        else:
            embedding_ranks = ranks
            position_embedding_ranks = ranks

        group = torch.distributed.new_group(embedding_ranks)
        if rank in embedding_ranks:
            _EMBEDDING_GROUP = group
        if rank in ranks:
            _EMBEDDING_GLOBAL_RANKS = embedding_ranks

        group = torch.distributed.new_group(position_embedding_ranks)
        if rank in position_embedding_ranks:
            _POSITION_EMBEDDING_GROUP = group
        if rank in ranks:
            _POSITION_EMBEDDING_GLOBAL_RANKS = position_embedding_ranks


def model_parallel_is_initialized():
    """Check if model and data parallel groups are initialized."""
    if _TENSOR_MODEL_PARALLEL_GROUP is None or \
        _PIPELINE_MODEL_PARALLEL_GROUP is None or \
        _DATA_PARALLEL_GROUP is None:
        return False
    return True


def get_model_parallel_group():
    """Get the model parallel group the caller rank belongs to."""
    assert _MODEL_PARALLEL_GROUP is not None, \
        'model parallel group is not initialized'
    return _MODEL_PARALLEL_GROUP


def get_tensor_model_parallel_group():
    """Get the tensor model parallel group the caller rank belongs to."""
    assert _TENSOR_MODEL_PARALLEL_GROUP is not None, \
        'intra_layer_model parallel group is not initialized'
    return _TENSOR_MODEL_PARALLEL_GROUP


def get_pipeline_model_parallel_group():
    """Get the pipeline model parallel group the caller rank belongs to."""
    assert _PIPELINE_MODEL_PARALLEL_GROUP is not None, \
        'pipeline_model parallel group is not initialized'
    return _PIPELINE_MODEL_PARALLEL_GROUP


def get_data_parallel_group():
    """Get the data parallel group the caller rank belongs to."""
    assert _DATA_PARALLEL_GROUP is not None, \
        'data parallel group is not initialized'
    return _DATA_PARALLEL_GROUP


def get_embedding_group():
    """Get the embedding group the caller rank belongs to."""
    assert _EMBEDDING_GROUP is not None, \
        'embedding group is not initialized'
    return _EMBEDDING_GROUP


def get_position_embedding_group():
    """Get the position embedding group the caller rank belongs to."""
    assert _POSITION_EMBEDDING_GROUP is not None, \
        'position embedding group is not initialized'
    return _POSITION_EMBEDDING_GROUP


def set_tensor_model_parallel_world_size(world_size):
    """Set the tensor model parallel size"""
    global _MPU_TENSOR_MODEL_PARALLEL_WORLD_SIZE
    _MPU_TENSOR_MODEL_PARALLEL_WORLD_SIZE = world_size


def set_pipeline_model_parallel_world_size(world_size):
    """Set the pipeline model parallel size"""
    global _MPU_PIPELINE_MODEL_PARALLEL_WORLD_SIZE
    _MPU_PIPELINE_MODEL_PARALLEL_WORLD_SIZE = world_size


def get_tensor_model_parallel_world_size():
    """Return world size for the tensor model parallel group."""
    global _MPU_TENSOR_MODEL_PARALLEL_WORLD_SIZE
    if _MPU_TENSOR_MODEL_PARALLEL_WORLD_SIZE is not None:
        return _MPU_TENSOR_MODEL_PARALLEL_WORLD_SIZE
    return torch.distributed.get_world_size(group=get_tensor_model_parallel_group())


def get_pipeline_model_parallel_world_size():
    """Return world size for the pipeline model parallel group."""
    global _MPU_PIPELINE_MODEL_PARALLEL_WORLD_SIZE
    if _MPU_PIPELINE_MODEL_PARALLEL_WORLD_SIZE is not None:
        return _MPU_PIPELINE_MODEL_PARALLEL_WORLD_SIZE
    return torch.distributed.get_world_size(group=get_pipeline_model_parallel_group())


def set_tensor_model_parallel_rank(rank):
    """Set tensor model parallel rank."""
    global _MPU_TENSOR_MODEL_PARALLEL_RANK
    _MPU_TENSOR_MODEL_PARALLEL_RANK = rank


def set_pipeline_model_parallel_rank(rank):
    """Set pipeline model parallel rank."""
    global _MPU_PIPELINE_MODEL_PARALLEL_RANK
    _MPU_PIPELINE_MODEL_PARALLEL_RANK = rank


def get_tensor_model_parallel_rank():
    """Return my rank for the tensor model parallel group."""
    global _MPU_TENSOR_MODEL_PARALLEL_RANK
    if _MPU_TENSOR_MODEL_PARALLEL_RANK is not None:
        return _MPU_TENSOR_MODEL_PARALLEL_RANK
    return torch.distributed.get_rank(group=get_tensor_model_parallel_group())


def get_pipeline_model_parallel_rank():
    """Return my rank for the pipeline model parallel group."""
    global _MPU_PIPELINE_MODEL_PARALLEL_RANK
    if _MPU_PIPELINE_MODEL_PARALLEL_RANK is not None:
        return _MPU_PIPELINE_MODEL_PARALLEL_RANK
    return torch.distributed.get_rank(group=get_pipeline_model_parallel_group())


def get_num_layers(args, is_encoder_and_decoder_model):
    """Compute the number of transformer layers resident on the current rank."""
    if get_pipeline_model_parallel_world_size() > 1:
        if is_encoder_and_decoder_model:
            assert args.pipeline_model_parallel_split_rank is not None

            # When a standalone embedding stage is used, a rank is taken from
            # the encoder's ranks, to be used for the encoder's embedding
            # layer. This way, the rank referenced by the 'split rank' remains
            # the same whether or not a standalone embedding stage is used.
            num_ranks_in_encoder = (
                args.pipeline_model_parallel_split_rank - 1
                if args.standalone_embedding_stage else
                args.pipeline_model_parallel_split_rank
            )
            num_ranks_in_decoder = args.transformer_pipeline_model_parallel_size - num_ranks_in_encoder
            assert args.num_layers % num_ranks_in_encoder == 0, \
                    'num_layers (%d) must be divisible by number of ranks given to encoder (%d)' % (args.num_layers, num_ranks_in_encoder)
            assert args.num_layers % num_ranks_in_decoder == 0, \
                    'num_layers (%d) must be divisible by number of ranks given to decoder (%d)' % (args.num_layers, num_ranks_in_decoder)
            if is_pipeline_stage_before_split():
                num_layers = (
                    0
                    if args.standalone_embedding_stage
                    and get_pipeline_model_parallel_rank() == 0 else
                    args.num_layers // num_ranks_in_encoder
                )
            else:
                num_layers = args.num_layers // num_ranks_in_decoder
        else:
            assert args.num_layers % args.transformer_pipeline_model_parallel_size == 0, \
                'num_layers must be divisible by transformer_pipeline_model_parallel_size'

            # When a standalone embedding stage is used, all transformer layers
            # are divided among pipeline rank >= 1, while on pipeline rank 0,
            # ranks either contain the input embedding layer (virtual pp rank 0),
            # or no layers at all (virtual pp rank >= 1).
            num_layers = (
                0
                if args.standalone_embedding_stage
                and get_pipeline_model_parallel_rank() == 0 else
                args.num_layers // args.transformer_pipeline_model_parallel_size
            )
    else:
        num_layers = args.num_layers
    return num_layers


def is_pipeline_first_stage(ignore_virtual=False):
    """Return True if in the first pipeline model-parallel stage, False otherwise."""
    if not ignore_virtual:
        if get_virtual_pipeline_model_parallel_world_size() is not None and \
            get_virtual_pipeline_model_parallel_rank() != 0:
            return False
    return get_pipeline_model_parallel_rank() == 0


def is_pipeline_last_stage(ignore_virtual=False):
    """Return True if in the last pipeline model-parallel stage, False otherwise."""
    if not ignore_virtual:
        virtual_pipeline_model_parallel_world_size = \
            get_virtual_pipeline_model_parallel_world_size()
        if virtual_pipeline_model_parallel_world_size is not None and \
            get_virtual_pipeline_model_parallel_rank() != (
                virtual_pipeline_model_parallel_world_size - 1):
            return False
    return get_pipeline_model_parallel_rank() == (
        get_pipeline_model_parallel_world_size() - 1)


def is_rank_in_embedding_group(ignore_virtual=False):
    """Return true if current rank is in embedding group, False otherwise."""
    rank = torch.distributed.get_rank()
    global _EMBEDDING_GLOBAL_RANKS
    if ignore_virtual:
        return rank in _EMBEDDING_GLOBAL_RANKS
    if rank in _EMBEDDING_GLOBAL_RANKS:
        if rank == _EMBEDDING_GLOBAL_RANKS[0]:
            return is_pipeline_first_stage(ignore_virtual=False)
        elif rank == _EMBEDDING_GLOBAL_RANKS[-1]:
            return is_pipeline_last_stage(ignore_virtual=False)
        else:
            return True
    return False


def is_rank_in_position_embedding_group():
    """Return true if current rank is in position embedding group, False otherwise."""
    rank = torch.distributed.get_rank()
    global _POSITION_EMBEDDING_GLOBAL_RANKS
    return rank in _POSITION_EMBEDDING_GLOBAL_RANKS


def is_pipeline_stage_before_split(rank=None):
    """Return True if pipeline stage executes encoder block for a model
    with both encoder and decoder."""
    if get_pipeline_model_parallel_world_size() == 1:
        return True
    if rank is None:
        rank = get_pipeline_model_parallel_rank()
    global _PIPELINE_MODEL_PARALLEL_SPLIT_RANK
    if _PIPELINE_MODEL_PARALLEL_SPLIT_RANK is None:
        return True
    if rank < _PIPELINE_MODEL_PARALLEL_SPLIT_RANK:
        return True
    return False


def is_pipeline_stage_after_split(rank=None):
    """Return True if pipeline stage executes decoder block for a model
    with both encoder and decoder."""
    if get_pipeline_model_parallel_world_size() == 1:
        return True
    if rank is None:
        rank = get_pipeline_model_parallel_rank()
    global _PIPELINE_MODEL_PARALLEL_SPLIT_RANK
    if _PIPELINE_MODEL_PARALLEL_SPLIT_RANK is None:
        return True
    if rank >= _PIPELINE_MODEL_PARALLEL_SPLIT_RANK:
        return True
    return False


def is_pipeline_stage_at_split():
    """Return true if pipeline stage executes decoder block and next
    stage executes encoder block for a model with both encoder and
    decoder."""
    rank = get_pipeline_model_parallel_rank()
    return is_pipeline_stage_before_split(rank) and \
            is_pipeline_stage_after_split(rank+1)


def get_virtual_pipeline_model_parallel_rank():
    """Return the virtual pipeline-parallel rank."""
    global _VIRTUAL_PIPELINE_MODEL_PARALLEL_RANK
    return _VIRTUAL_PIPELINE_MODEL_PARALLEL_RANK


def set_virtual_pipeline_model_parallel_rank(rank):
    """Set the virtual pipeline-parallel rank."""
    global _VIRTUAL_PIPELINE_MODEL_PARALLEL_RANK
    _VIRTUAL_PIPELINE_MODEL_PARALLEL_RANK = rank


def get_virtual_pipeline_model_parallel_world_size():
    """Return the virtual pipeline-parallel world size."""
    global _VIRTUAL_PIPELINE_MODEL_PARALLEL_WORLD_SIZE
    return _VIRTUAL_PIPELINE_MODEL_PARALLEL_WORLD_SIZE


def get_tensor_model_parallel_src_rank():
    """Calculate the global rank corresponding to the first local rank
    in the tensor model parallel group."""
    global_rank = torch.distributed.get_rank()
    local_world_size = get_tensor_model_parallel_world_size()
    return (global_rank // local_world_size) * local_world_size


def get_data_parallel_src_rank():
    """Calculate the global rank corresponding to the first local rank
    in the data parallel group."""
    assert _DATA_PARALLEL_GLOBAL_RANKS is not None, \
        "Data parallel group is not initialized"
    return _DATA_PARALLEL_GLOBAL_RANKS[0]


def get_pipeline_model_parallel_first_rank():
    assert _PIPELINE_GLOBAL_RANKS is not None, \
        "Pipeline parallel group is not initialized"
    return _PIPELINE_GLOBAL_RANKS[0]


def get_pipeline_model_parallel_last_rank():
    assert _PIPELINE_GLOBAL_RANKS is not None, \
        "Pipeline parallel group is not initialized"
    last_rank_local = get_pipeline_model_parallel_world_size() - 1
    return _PIPELINE_GLOBAL_RANKS[last_rank_local]

def get_pipeline_model_parallel_next_rank():
    assert _PIPELINE_GLOBAL_RANKS is not None, \
        "Pipeline parallel group is not initialized"
    rank_in_pipeline = get_pipeline_model_parallel_rank()
    world_size = get_pipeline_model_parallel_world_size()
    return _PIPELINE_GLOBAL_RANKS[(rank_in_pipeline + 1) % world_size]


def get_pipeline_model_parallel_prev_rank():
    assert _PIPELINE_GLOBAL_RANKS is not None, \
        "Pipeline parallel group is not initialized"
    rank_in_pipeline = get_pipeline_model_parallel_rank()
    world_size = get_pipeline_model_parallel_world_size()
    return _PIPELINE_GLOBAL_RANKS[(rank_in_pipeline - 1) % world_size]


def get_data_parallel_world_size():
    """Return world size for the data parallel group."""
    return torch.distributed.get_world_size(group=get_data_parallel_group())


def get_data_parallel_rank():
    """Return my rank for the data parallel group."""
    return torch.distributed.get_rank(group=get_data_parallel_group())


def destroy_model_parallel():
    """Set the groups to none."""
    global _MODEL_PARALLEL_GROUP
    _MODEL_PARALLEL_GROUP = None
    global _TENSOR_MODEL_PARALLEL_GROUP
    _TENSOR_MODEL_PARALLEL_GROUP = None
    global _PIPELINE_MODEL_PARALLEL_GROUP
    _PIPELINE_MODEL_PARALLEL_GROUP = None
    global _DATA_PARALLEL_GROUP
    _DATA_PARALLEL_GROUP = None
    global _EMBEDDING_GROUP
    _EMBEDDING_GROUP = None
    global _POSITION_EMBEDDING_GROUP
    _POSITION_EMBEDDING_GROUP = None