configs

Configuration and parameters

GPT-NeoX parameters are defined in a YAML configuration file which is passed to the deepy.py launcher - for examples see the files contained in this folder. Parameters originate from either the DeepSpeed runner CLI (DSL), DeepSpeed configuration file (DSC), Megatron-LM CLI (Meg) or are GPT-NeoX (NeoX) modifications.

Example Configuration (GPT3 Small):

Below is an example configuration .yaml to train a ~160M parameter GPT model. This readme will go through each section in the configuration and the options available.

For a detailed list of all the arguments available for neox, see neox_arguments.md

# GPT-3 pretraining setup
{
   # parallelism settings ( you will want to change these based on your cluster setup, ideally scheduling pipeline stages
   # across the node boundaries )
   "pipe-parallel-size": 1,
   "model-parallel-size": 1,

   # model settings
   "num-layers": 12,
   "hidden-size": 768,
   "num-attention-heads": 12,
   "seq-length": 2048,
   "max-position-embeddings": 2048,
   "norm": "rmsnorm",
   "pos-emb": "none",
   "no-weight-tying": true,
    # this should provide some speedup but takes a while to build, set to true if desired
   "scaled-upper-triang-masked-softmax-fusion": false,
   "train-iters": 320000,

   # optimizer settings
   "optimizer": {
     "type": "Adam",
     "params": {
       "lr": 0.0006,
       "max_grad_norm": 1.0,
       "betas": [0.9, 0.95]
     }
   },
   # for all zero_optimization options, see https://www.deepspeed.ai/docs/config-json/#zero-optimizations-for-fp16-training
   "zero_optimization": {
    "stage": 0,
    "allgather_partitions": True,
    "allgather_bucket_size": 500000000,
    "overlap_comm": True,
    "reduce_scatter": True,
    "reduce_bucket_size": 500000000,
    "contiguous_gradients": True,
  },

   # batch / data settings
   "train_micro_batch_size_per_gpu": 4,
   "gradient_accumulation_steps": 1,
   "data-impl": "mmap",
   "split": "949,50,1",

   # activation checkpointing
   "checkpoint-activations": true,
   "checkpoint-num-layers": 1,
   "partition-activations": true,
   "synchronize-each-layer": true,

   # regularization
   "gradient_clipping": 1.0,
   "weight-decay": 0,
   "hidden-dropout": 0,
   "attention-dropout": 0,

   # precision settings
   "fp16": {
     "enabled": true,
     "loss_scale": 0,
     "loss_scale_window": 1000,
     "hysteresis": 2,
     "min_loss_scale": 1
   },

   # lr decay settings
   "lr-decay-iters": 320000,
   "lr-decay-style": "cosine",
   "warmup": 0.01,

   # misc. training settings
   "distributed-backend": "nccl",
   "save-interval": 10000,
   "eval-interval": 1000,
   "eval-iters": 10,

   # logging
   "log-interval": 100,
   "steps_per_print": 10,
   "keep-last-n-checkpoints": 4,
   "wall_clock_breakdown": true,
}

Parallelism Settings:

The parallelism settings are left at 1 in all configs, as the settings you want will be highly dependent on your compute setup and network topology. We have found it best to do model parallelism within a node, and schedule pipeline stages across node boundaries.

   "pipe-parallel-size": 1,
   "model-parallel-size": 1,

These can be set to any integer between 0 and num_gpus, and num_gpus must be divisible by pipe_parallel_size * model_parallel_size.

Model Settings:

   # model settings
   "num-layers": 12,
   "hidden-size": 768,
   "num-attention-heads": 12,
   "seq-length": 2048,
   "max-position-embeddings": 2048,
   "norm": "rmsnorm",
   "pos-emb": "none",
   "no-weight-tying": true,
    # this should provide some speedup but takes a while to build, set to true if desired
   "scaled-upper-triang-masked-softmax-fusion": false,
   "train-iters": 320000,

An example of some basic settings used to configure your model's architecture and number of training steps.

Optimizer Settings:

Our optimizer configuration has a similar syntax to deepspeed's. Different optimizers will have different arguments for "params". Learning rate should be configured from here using the "lr" field of optimizer["params"].

  # optimizer settings
   "optimizer": {
     "type": "Adam",
     "params": {
       "lr": 0.0006,
       "max_grad_norm": 1.0,
       "betas": [0.9, 0.95]
     }
   }

Available optimizer types are:

• "Adam": regular Adam optimizer
• "OneBitAdam": Deepspeed's OneBitAdam optimizer. To use 1-bit adam, you'll also need to add the freeze_step, cuda_aware, and comm_backend_name fields, like so:

   "optimizer": {
     "type": "OneBitAdam",
     "params": {
       "lr": 0.0001,
       "freeze_step": 23000,
       "betas": [0.9, 0.95],
       "cuda_aware": false,
       "comm_backend_name": "nccl"
     }

• "CPU_Adam"/"CPU_torch_adam": Adam optimizer on CPU. Either megatron's version ("CPU_Adam") or torch's ("CPU_torch_adam")
• "SM3": SM3 or Memory adaptive efficient optimization optimizer. We have found this doesn't work well with fp16 training.
• "madgrad_wd": MADGRAD or [A Momentumized, Adaptive, Dual Averaged Gradient Method for Stochastic Optimizer] weight decay has been implemented AdamW style instead of the original madgrad Adam style. https://arxiv.org/abs/2101.11075

ZeRO Optimization:

# for all zero_optimization options, see https://www.deepspeed.ai/docs/config-json/#zero-optimizations-for-fp16-training
  "zero_optimization": {
        "stage": 0,
        "allgather_partitions": True,
        "allgather_bucket_size": 500000000,
        "overlap_comm": True,
        "reduce_scatter": True,
        "reduce_bucket_size": 500000000,
        "contiguous_gradients": True,
  },
  "zero_allow_untested_optimizer": false,

ZeRO optimization in NeoX is currently configured identically to how deepspeed configures it, please see the deepspeed docs for more information.

If you want to combine an optimizer untested by DeepSpeed with ZeRO (i.e, not ADAM or LAMB), you must pass "zero_allow_untested_optimizer": true outside of the "zero_optimization" dictionary (see above).

N.B - ZeRO stages 2+ are incompatible with pipeline parallelism. Please set "pipe-parallel-size" to 0 if you want to use ZeRO stage 2 or more.

Batch Size Settings:

   # batch / data settings
   "train_micro_batch_size_per_gpu": 4,
   "gradient_accumulation_steps": 1,

Our global batch size configuration follows deepspeed's and can be configured in a number of ways. At least any one of "train_batch_size" and "train_micro_batch_size_per_gpu".

• "train_batch_size": The effective training batch size. This is the amount of data samples that leads to one step of model update. train_batch_size is aggregated by the batch size that a single GPU processes in one forward/backward pass (a.k.a., train_step_batch_size), the gradient accumulation steps (a.k.a., gradient_accumulation_steps), and the number of GPUs.
• "train_micro_batch_size_per_gpu"": Batch size to be processed by one GPU in one step (without gradient accumulation). When specified, gradient_accumulation_steps is automatically calculated using train_batch_size and number of GPUs.
• "gradient_accumulation_steps": Number of training steps to accumulate gradients before averaging and applying them. This feature is sometimes useful to improve scalability since it results in less frequent communication of gradients between steps. Another impact of this feature is the ability to train with larger batch sizes per GPU. When specified, train_step_batch_size is automatically calculated using train_batch_size and number of GPUs.

Dataset / Tokenizer / Checkpoint / Logging Settings:

   "data-impl": "mmap",
   "split": "949,50,1",
   # Suggested data paths when using GPT-NeoX locally
   "data-path": "data/enwik8/enwik8_text_document",
   #"train-data-path": "data/enwik8/enwik8_text_document",
   #"test-data-path": "data/enwik8/enwik8_text_document",
   #"valid-data-path": "data/enwik8/enwik8_text_document",
   "vocab-file": "data/gpt2-vocab.json",
   "merge-file": "data/gpt2-merges.txt",
   "save": "checkpoints",
   "load": "checkpoints",
   "tensorboard-dir": "tensorboard",
   "log-dir": "logs",
   "save-interval": 10000,
   "eval-interval": 1000,
   "eval-iters": 10,

LR Scheduler settings

   "lr-decay-iters": 320000,
   "lr-decay-style": "cosine",
   "warmup": 0.01,

Settings used to modify the learning rate over time.

N.B - OneBitAdam requires you to use deepspeed's internal lr scheduler because reasons. Currently the lr decay style defaults to deepspeed's `WarmupDecay

Activation Checkpointing Settings:

   "checkpoint-activations": true,
   "checkpoint-num-layers": 1,
   "partition-activations": true,
   "synchronize-each-layer": true,

Checkpointing works by trading compute for memory. Rather than storing all intermediate activations of the entire computation graph for computing backward, the checkpointed part does not save intermediate activations, and instead recomputes them in backward pass.

Mixed Precision Training Settings:

gpt-neox's mixed precision training is configured identically to DeepSpeed's, please see their documentation for more information. An example config for fp16 training:

   "fp16": {
     "enabled": true,
     "loss_scale": 0,
     "loss_scale_window": 1000,
     "hysteresis": 2,
     "min_loss_scale": 1
   },

To train in fp32, simply set fp16["enabled"] to false.

SLURM Settings

If you are running GPT-NeoX on a SLURM cluster and wish to use SLURM to coordinate nodes, then you must set the following variables in your config:

    "launcher": "slurm",
    "deepspeed_slurm": true

Additionally, you need to modify all of your configs to conform to the JSON. When launching a GPT-NeoX job you can specify multiple YAML config files. Internally, all of these files are merged into one config and then passed as a single long command line argument to Deep(er)Speed. When using SLURM and its internal command srun, python fails to parse this long command line argument unless it is in the more restrictive JSON format. In practice, the example NeoX configs are already very close to JSON. As an example, this is a snippet of a YAML-compatible config, N.B. the comment the capital-F False:

    # optimizer settings
   "optimizer": {
     "type": "OneBitAdam",
     "params": {
       "lr": 0.0001,
       "freeze_step": 23000,
       "betas": [0.9, 0.95],
       "cuda_aware": False,
       "comm_backend_name": "nccl"
     }

To make this JSON just remove the comment and use all lowercase for the boolean:

   "optimizer": {
     "type": "OneBitAdam",
     "params": {
       "lr": 0.0001,
       "freeze_step": 23000,
       "betas": [0.9, 0.95],
       "cuda_aware": false,
       "comm_backend_name": "nccl"
     }

** TODO: bf16 docs **