Source code for

# Copyright (c) Microsoft Corporation.
# SPDX-License-Identifier: Apache-2.0

# DeepSpeed Team

from typing import Optional, Tuple

import torch
from torch import nn
from torch.nn import functional as F

from deepspeed.utils import groups, log_dist
from .experts import Experts
from .sharded_moe import MOELayer, TopKGate

[docs]class MoE(nn.Module): """Initialize an MoE layer. Arguments: hidden_size (int): the hidden dimension of the model, importantly this is also the input and output dimension. expert (nn.Module): the torch module that defines the expert (e.g., MLP, torch.linear). num_experts (int, optional): default=1, the total number of experts per layer. ep_size (int, optional): default=1, number of ranks in the expert parallel world or group. k (int, optional): default=1, top-k gating value, only supports k=1 or k=2. capacity_factor (float, optional): default=1.0, the capacity of the expert at training time. eval_capacity_factor (float, optional): default=1.0, the capacity of the expert at eval time. min_capacity (int, optional): default=4, the minimum capacity per expert regardless of the capacity_factor. use_residual (bool, optional): default=False, make this MoE layer a Residual MoE ( layer. noisy_gate_policy (str, optional): default=None, noisy gate policy, valid options are 'Jitter', 'RSample' or 'None'. drop_tokens (bool, optional): default=True, whether to drop tokens - (setting to False is equivalent to infinite capacity). use_rts (bool, optional): default=True, whether to use Random Token Selection. use_tutel (bool, optional): default=False, whether to use Tutel optimizations (if installed). enable_expert_tensor_parallelism (bool, optional): default=False, whether to use tensor parallelism for experts top2_2nd_expert_sampling (bool, optional): default=True, whether to perform sampling for 2nd expert """ def __init__(self, hidden_size: int, expert: nn.Module, num_experts: int = 1, ep_size: int = 1, k: int = 1, capacity_factor: float = 1.0, eval_capacity_factor: float = 1.0, min_capacity: int = 4, use_residual: bool = False, noisy_gate_policy: Optional[str] = None, drop_tokens: bool = True, use_rts: bool = True, use_tutel: bool = False, enable_expert_tensor_parallelism: bool = False, top2_2nd_expert_sampling: bool = True) -> None: super(MoE, self).__init__() self.use_residual = use_residual self.enable_expert_tensor_parallelism = enable_expert_tensor_parallelism assert num_experts % ep_size == 0, f"Number of experts ({num_experts}) should be divisible by expert parallel size ({ep_size})" self.ep_size = ep_size self.expert_group_name = f"ep_size_{self.ep_size}" self.num_experts = num_experts self.num_local_experts = num_experts // self.ep_size log_dist( f'Creating MoE layer with num_experts: {num_experts} | num_local_experts: {self.num_local_experts} | expert_parallel_size: {self.ep_size}', [0]) assert noisy_gate_policy is None or noisy_gate_policy in ['None', 'Jitter', 'RSample'], \ 'Unsupported noisy_gate_policy: ' + noisy_gate_policy experts = Experts(expert, self.num_local_experts, self.expert_group_name) self.deepspeed_moe = MOELayer(TopKGate(hidden_size, num_experts, k, capacity_factor, eval_capacity_factor, min_capacity, noisy_gate_policy, drop_tokens, use_rts, None, top2_2nd_expert_sampling), experts, self.expert_group_name, self.ep_size, self.num_local_experts, use_tutel=use_tutel) if self.use_residual: self.mlp = expert # coefficient is used for weighted sum of the output of expert and mlp self.coefficient = nn.Linear(hidden_size, 2) def set_deepspeed_parallelism(self, use_data_before_expert_parallel_: bool = False) -> None: self._create_process_groups(use_data_before_expert_parallel_=use_data_before_expert_parallel_) def _create_process_groups(self, use_data_before_expert_parallel_: bool = False) -> None: # Create process group for a layer if needed if self.expert_group_name not in groups._get_expert_parallel_group_dict(): print(f"No existing process group found, creating a new group named: {self.expert_group_name}") if (groups.mpu is None) or (not self.enable_expert_tensor_parallelism): # Condition 1 - no groups.mpu means no tensor parallelism # Condition 2 - disabling expert tensor parallelism on purpose groups._create_expert_and_data_parallel( self.ep_size, use_data_before_expert_parallel_=use_data_before_expert_parallel_) else: # expert tensor parallelism is enabled groups._create_expert_data_and_model_parallel( self.ep_size, mpu=groups.mpu, use_data_before_expert_parallel_=use_data_before_expert_parallel_) # Set the group handle for the MOELayer (deepspeed_moe) object self.deepspeed_moe._set_ep_group(groups._get_expert_parallel_group(self.expert_group_name))
[docs] def forward(self, hidden_states: torch.Tensor, used_token: Optional[torch.Tensor] = None) -> Tuple[torch.Tensor, torch.Tensor, torch.Tensor]: """ MoE forward Arguments: hidden_states (Tensor): input to the layer used_token (Tensor, optional): default: None, mask only used tokens Returns: A tuple including output, gate loss, and expert count. * output (Tensor): output of the model * l_aux (Tensor): gate loss value * exp_counts (Tensor): expert count """ output = self.deepspeed_moe(hidden_states, used_token) if self.use_residual: # Residual MoE output_mlp = self.mlp(hidden_states) if isinstance(output_mlp, tuple): output_mlp = output_mlp[0] # Ignore the bias term for now coef = self.coefficient(hidden_states) coef = F.softmax(coef, dim=-1) output = output * coef[..., 0:1] + output_mlp * coef[..., 1:] return output, self.deepspeed_moe.l_aux, self.deepspeed_moe.exp_counts