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Accelerator: HPU Training

This document offers instructions to Gaudi chip users who want to conserve memory and scale models using mixed-precision training.


Enable Mixed Precision

With Lightning, you can leverage mixed precision training on HPUs. By default, HPU training uses 32-bit precision. To enable mixed precision, set the precision flag.

from lightning_habana.pytorch.accelerator import HPUAccelerator

trainer = Trainer(devices=1, accelerator=HPUAccelerator(), precision="bf16-mixed")

Customize Mixed Precision Using Autocast

Lightning supports following methods to enable mixed precision training with HPU.

HPUPrecisionPlugin

HPUPrecisionPlugin, HPUPrecisionPlugin enables mixed precision training on Habana devices.

In addition to the default settings, you can choose to override these defaults and provide your own BF16 (LOWER_LIST) and FP32 (FP32_LIST) The LOWER_LIST and FP32_LIST environment variables must be set before any instances begin.

The following is an excerpt from an MNIST example implemented on a single HPU.

from lightning import Trainer
from lightning_habana.pytorch.accelerator import HPUAccelerator
from lightning_habana.pytorch.plugins.precision import HPUPrecisionPlugin

# Initialize a trainer with HPU accelerator for HPU strategy for single device,
# with HPU precision plugin for autocast
trainer = Trainer(
    accelerator=HPUAccelerator(),
    devices=1,
    plugins=[
        HPUPrecisionPlugin(
            precision="bf16-mixed",
        )
    ],
)

# Init our model
model = LitClassifier()
# Init the data
dm = MNISTDataModule(batch_size=batch_size)

# Train the model ⚡
trainer.fit(model, datamodule=dm)

Native PyTorch torch.autocast()

For more granular control over with mixed precision training, one can use torch.autocast from native PyTorch.

Instances of autocast serve as context managers or decorators that allow regions of your script to run in mixed precision. These also allow for fine tuning with enabled for enabling and disabling mixed precision training for certain parts of the code.

import torch
from lightning import Trainer

class AutocastModelCM(nn.Module):
    # Autocast can be used as a context manager to the required code block.
    def forward(self, input):
        with torch.autocast(device_type="hpu", dtype=torch.bfloat16):
        ...
        return

class AutocastModelDecorator(nn.Module):
    # Autocast can be used as a decorator to the required code block.
    @torch.autocast(device_type="hpu", dtype=torch.bfloat16)
    def forward(self, input):
        ...
        return

# Initialize a trainer with HPU accelerator for HPU strategy for single device,
# with mixed precision using overridden HMP settings
trainer = Trainer(
    accelerator="hpu",
    devices=1,
)

# Init our model
model = AutocastModelCM()
# Init the data
dm = MNISTDataModule(batch_size=batch_size)

# Train the model ⚡
trainer.fit(model, datamodule=dm)

For more details, please refer to Native PyTorch Autocast. and Automatic Mixed Precision Package: torch.autocast.


fp8 Training

Lightning supports fp8 training using HPUPrecisionPlugin, HPUPrecisionPlugin. fp8 training is only available on Gaudi2 and above. Output from fp8 supported modules is in torch.bfloat16.

The plugin accepts following args for the fp8 training:

  1. replace_layers : Set True to let the plugin replace torch.nn.Modules with trandformer_engine equivalent modules. You can directly import and use modules from transformer_engine as well.

  2. recipe : fp8 recipe used in training.

from lightning import Trainer
from lightning_habana.pytorch.accelerator import HPUAccelerator
from lightning_habana.pytorch.plugins.precision import HPUPrecisionPlugin
from habana_frameworks.torch.hpex.experimental.transformer_engine import recipe

model = BoringModel()

# init the precision plugin for fp8 training.
plugin = HPUPrecisionPlugin(precision="fp8", replace_layers=True, recipe=recipe.DelayedScaling())

# Replace torch.nn.Modules with transformer engine equivalent modules
plugin.replace_modules(model)

# Initialize a trainer with HPUPrecisionPlugin
trainer = Trainer(
    accelerator=HPUAccelerator(),
    plugins=plugin
)

# Train the model ⚡
trainer.fit(model)

For more details, recipes, and list of supported transformer_engine modules, refer to FP8 Training with Intel Gaudi Transformer Engine.


Enabling DeviceStatsMonitor with HPUs

DeviceStatsMonitor is a callback that automatically monitors and logs device stats during the training stage. This callback can be passed for training with HPUs. It returns a map of the following metrics with their values in bytes of type uint64:

Metric

Value

Limit

Amount of total memory on HPU.

InUse

Amount of allocated memory at any instance.

MaxInUse

Amount of total active memory allocated.

NumAllocs

Number of allocations.

NumFrees

Number of freed chunks.

ActiveAllocs

Number of active allocations.

MaxAllocSize

Maximum allocated size.

TotalSystemAllocs

Total number of system allocations.

TotalSystemFrees

Total number of system frees.

TotalActiveAllocs

Total number of active allocations.

The below shows how DeviceStatsMonitor can be enabled.

from lightning import Trainer
from lightning.callbacks import DeviceStatsMonitor
from lightning_habana.pytorch.accelerator import HPUAccelerator

device_stats = DeviceStatsMonitor()
trainer = Trainer(accelerator=HPUAccelerator(), callbacks=[device_stats])

For more details, please refer to Memory Stats APIs.


Runtime Environment Variables

Habana runtime environment flags are used to change the behavior as well as enable or disable some features.

For more information, refer to Runtime Flags.