Accelerator: HPU Training¶

This document offers instructions to Gaudi chip users who want to use advanced strategies and profiling HPUs.

Using HPUProfiler¶

HPUProfiler is a Lightning implementation of PyTorch profiler for HPU. It aids in obtaining profiling summary of PyTorch functions. It subclasses PyTorch Lightning’s PyTorch profiler.

Default Profiling¶

For auto profiling, create an HPUProfiler instance and pass it to the trainer. At the end of profiler.fit(), it will generate a JSON trace for the run. In case accelerator= HPUAccelerator() is not used with HPUProfiler, it will dump only CPU traces, similar to PyTorchProfiler.

from lightning import Trainer
from lightning_habana.pytorch.accelerator import HPUAccelerator
from lightning_habana.pytorch.profiler.profiler import HPUProfiler

trainer = Trainer(accelerator=HPUAccelerator(), profiler=HPUProfiler())

Distributed Profiling¶

To profile a distributed model, use HPUProfiler with the filename argument which will save a report per rank.

from lightning import Trainer
from lightning_habana.pytorch.accelerator import HPUAccelerator
from lightning_habana.pytorch.profiler.profiler import HPUProfiler

profiler = HPUProfiler(filename="perf-logs")
trainer = Trainer(profiler=profiler, accelerator=HPUAccelerator())

Custom Profiling¶

To profile custom actions of interest, reference a profiler in the LightningModule.

from lightning import Trainer
from lightning_habana.pytorch.accelerator import HPUAccelerator
from lightning_habana.pytorch.profiler.profiler import HPUProfiler

# Reference profiler in LightningModule
class MyModel(LightningModule):
    def __init__(self, profiler=None):
        self.profiler = profiler

# To profile in any part of your code, use the self.profiler.profile() function
    def custom_processing_step_basic(self, data):
        with self.profiler.profile("my_custom_action"):
            print("do something")
        return data

# Alternatively, use self.profiler.start("my_custom_action")
# and self.profiler.stop("my_custom_action") functions
# to enclose the part of code to be profiled.
    def custom_processing_step_granular(self, data):
        self.profiler.start("my_custom_action")
        print("do something")
        self.profiler.stop("my_custom_action")
        return data

# Pass profiler instance to LightningModule
profiler = HPUProfiler()
model = MyModel(profiler)
trainer = Trainer(accelerator=HPUAccelerator(), profiler=profiler)

For more details on Profiler, refer to PyTorchProfiler

Visualizing Profiled Operations¶

Profiler dumps traces in JSON format. The traces can be visualized in 2 ways as described below.

Using PyTorch TensorBoard Profiler¶

For further instructions see, https://github.com/pytorch/kineto/tree/master/tb_plugin.

Install tensorboard

python -um pip install tensorboard torch-tb-profiler

Start the TensorBoard server (default at port 6006)

tensorboard --logdir ./tensorboard --port 6006

Open the following URL in your browser: http://localhost:6006/#profile.

Using Chrome¶

Open Chrome and paste this URL: chrome://tracing/.

Once tracing opens, click on Load at the top-right and load one of the generated traces.

Limitations¶

When using HPUProfiler, wall clock time will not be representative of the true wall clock time. This is due to forcing profiled operations to be measured synchronously, when many HPU ops happen asynchronously. It is recommended to use this Profiler to find bottlenecks/breakdowns, however for end to end wall clock time use the SimpleProfiler.
HPUProfiler.summary() is not supported.
Passing the Profiler name as a string “hpu” to the trainer is not supported.

Using DeepSpeed¶

HPU supports advanced optimization libraries like deepspeed. The HabanaAI GitHub has a fork of the DeepSpeed library that includes changes to add support for SynapseAI.

Installing DeepSpeed for HPU¶

To use DeepSpeed with Lightning on Gaudi, you must install Habana’s fork for DeepSpeed. To install the latest supported version of DeepSpeed, follow the instructions at https://docs.habana.ai/en/latest/PyTorch/DeepSpeed/DeepSpeed_User_Guide/DeepSpeed_User_Guide.html#installing-deepspeed-library

Using DeepSpeed on HPU¶

In Lightning, Deepspeed functionalities are enabled for HPU via HPUDeepSpeedStrategy. By default, HPU training uses 32-bit precision. To enable mixed precision, set the precision flag. A basic example of HPUDeepSpeedStrategy invocation is shown below.

class DemoModel(LightningModule):

    ...

    def configure_optimizers(self) -> Tuple[List[torch.optim.Optimizer], List[_TORCH_LRSCHEDULER]]:
        optimizer = torch.optim.SGD(self.layer.parameters(), lr=0.1)
        lr_scheduler = torch.optim.lr_scheduler.StepLR(optimizer, step_size=1)
        return [optimizer], [lr_scheduler]

model = DemoModel()
_plugins = [DeepSpeedPrecisionPlugin(precision="bf16-mixed")]
trainer = Trainer(
    accelerator=HPUAccelerator(), strategy=HPUDeepSpeedStrategy(),
    callbacks=[TestCB()], max_epochs=1, plugins=_plugins,
)
trainer.fit(model)

Note

accelerator=”auto” or accelerator=”hpu” is not yet enabled with lightning>2.0.0 and lightning-habana.
Passing strategy in a string representation (“hpu_deepspeed”, “hpu_deepspeed_stage_1”, etc.. ) are not yet enabled.

DeepSpeed Configurations¶

Below is a summary of all the DeepSpeed configurations supported by HPU. For full details on the HPU supported DeepSpeed features and functionalities, refer to Using Deepspeed with HPU. All further information on DeepSpeed configurations can be found in DeepSpeed<https://www.deepspeed.ai/training/#features> documentation.

ZeRO-1
ZeRO-2
ZeRO-3
ZeRO-Offload
ZeRO-Infinity
BF16 precision
BF16Optimizer
Activation Checkpointing

The HPUDeepSpeedStrategy can be configured using its arguments or a JSON configuration file. Both configuration methods are shown in the examples below.

ZeRO-1¶

from lightning.pytorch.plugins import DeepSpeedPrecisionPlugin
from lightning_habana.pytorch.accelerator import HPUAccelerator
from lightning_habana.pytorch.strategies import HPUDeepSpeedStrategy

trainer = Trainer(devices=8, accelerator=HPUAccelerator(), strategy=HPUDeepSpeedStrategy(zero_optimization=True, stage=1), plugins=[DeepSpeedPrecisionPlugin(precision="bf16-mixed")])

ZeRO-2¶

from lightning.pytorch.plugins import DeepSpeedPrecisionPlugin
from lightning_habana.pytorch.accelerator import HPUAccelerator
from lightning_habana.pytorch.strategies import HPUDeepSpeedStrategy

trainer = Trainer(devices=8, accelerator=HPUAccelerator(), strategy=HPUDeepSpeedStrategy(zero_optimization=True, stage=2), plugins=[DeepSpeedPrecisionPlugin(precision="bf16-mixed")])

ZeRO-3¶

from lightning.pytorch.plugins import DeepSpeedPrecisionPlugin
from lightning_habana.pytorch.accelerator import HPUAccelerator
from lightning_habana.pytorch.strategies import HPUDeepSpeedStrategy

trainer = Trainer(devices=8, accelerator=HPUAccelerator(), strategy=HPUDeepSpeedStrategy(zero_optimization=True, stage=3), plugins=[DeepSpeedPrecisionPlugin(precision="bf16-mixed")])

ZeRO-Offload¶

from lightning.pytorch.plugins import DeepSpeedPrecisionPlugin
from lightning_habana.pytorch.accelerator import HPUAccelerator
from lightning_habana.pytorch.strategies import HPUDeepSpeedStrategy

trainer = Trainer(devices=8, accelerator=HPUAccelerator(), strategy=HPUDeepSpeedStrategy(zero_optimization=True, stage=2, offload_optimizer=True), plugins=[DeepSpeedPrecisionPlugin(precision="bf16-mixed")])

ZeRO-Infinity¶

from lightning.pytorch.plugins import DeepSpeedPrecisionPlugin
from lightning_habana.pytorch.accelerator import HPUAccelerator
from lightning_habana.pytorch.strategies import HPUDeepSpeedStrategy

trainer = Trainer(devices=8, accelerator=HPUAccelerator(), strategy=HPUDeepSpeedStrategy(zero_optimization=True, stage=2, offload_optimizer=True), plugins=[DeepSpeedPrecisionPlugin(precision="bf16-mixed")])

BF16 precision¶

from lightning.pytorch.plugins import DeepSpeedPrecisionPlugin
from lightning_habana.pytorch.accelerator import HPUAccelerator
from lightning_habana.pytorch.strategies import HPUDeepSpeedStrategy

trainer = Trainer(devices=8, accelerator=HPUAccelerator(), strategy=HPUDeepSpeedStrategy(), plugins=[DeepSpeedPrecisionPlugin(precision="bf16-mixed")])

BF16-Optimizer¶

This example demonstrates how the HPUDeepSpeedStrategy can be configured using a DeepSpeed json configuration.

from lightning.pytorch import LightningModule, Trainer
from lightning_habana.pytorch.accelerator import HPUAccelerator
from lightning_habana.pytorch.strategies import HPUDeepSpeedStrategy

config = {
    "train_batch_size": 8,
    "bf16": {
        "enabled": True
    },
    "fp16": {
        "enabled": False
    },
    "train_micro_batch_size_per_gpu": 2,
    "scheduler": {
        "type": "WarmupDecayLR",
        "params": {
        "warmup_min_lr": 0.02,
        "warmup_max_lr": 0.05,
        "warmup_num_steps": 4,
        "total_num_steps" : 8,
        "warmup_type": "linear"
        }
    },
    "zero_allow_untested_optimizer": True,
    "zero_optimization": {"stage" : 2}
}


class SampleModel(LightningModule):
    ...

    def configure_optimizers(self):
        from torch.optim.adamw import AdamW as AdamW
        optimizer = torch.optim.AdamW(self.parameters())
        return optimizer


_plugins = [DeepSpeedPrecisionPlugin(precision="bf16-mixed")]
_accumulate_grad_batches=2
_parallel_hpus = [torch.device("hpu")] * HPUAccelerator.auto_device_count()

model = SampleModel()
trainer = Trainer(
    accelerator=HPUAccelerator(), strategy=HPUDeepSpeedStrategy(config=config, parallel_devices=_parallel_hpus),
    enable_progress_bar=False,
    fast_dev_run=8,
    plugins=_plugins,
    use_distributed_sampler=False,
    limit_train_batches=16,
    accumulate_grad_batches=_accumulate_grad_batches,
)

trainer.fit(model)

Note

When the optimizer and/or scheduler configuration is specified in both LightningModule and DeepSpeed json configuration file, preference will be given to the optimizer/scheduler returned by LightningModule::configure_optimizers().

Activation Checkpointing¶

from lightning.pytorch import LightningModule, Trainer
from lightning_habana.pytorch.accelerator import HPUAccelerator
from lightning_habana.pytorch.strategies import HPUDeepSpeedStrategy
from deepspeed.runtime.activation_checkpointing.checkpointing import checkpoint

class SampleModel(LightningModule):
    def __init__(self):
        super().__init__()
        self.l1 = nn.Linear(32)
        self.l2 = nn.Linear(32)

    def forward(self, x):
        l1_out = self.l1(x)
        l2_out = checkpoint(self.l2, l1_out)
        return l2_out

trainer = Trainer(accelerator=HPUAccelerator(),
                    strategy=HPUDeepSpeedStrategy(zero_optimization=True,
                                                    stage=3,
                                                    offload_optimizer=True,
                                                    cpu_checkpointing=True),
                    plugins=[DeepSpeedPrecisionPlugin(precision="bf16-mixed")]
                )

Limitations of DeepSpeed on HPU¶

DeepSpeed Zero Stage 3 is not yet supported by Gaudi2.

Offloading to Nvme is not yet verified on HPU with DeepSpeed Zero Stage 3 Offload configuration.

Model Pipeline and Tensor Parallelism are currently supported only on Gaudi2.

For further details on the supported DeepSpeed features and functionalities, refer to Using Deepspeed with HPU.

Using HPU Graphs¶

HPU Graphs reduce training and inference time for large models running in Lazy Mode. HPU Graphs bypasses all op accumulations by recording a static version of the entire graph, then replaying it. The speedup achieved by using HPU Graphs depends on the underlying model. HPU Graphs reduce host overhead significantly, and can be used to speed up the process when it is host bound.

For further details, refer to Using HPU Graphs for Training and Run Inference Using HPU Graphs

HPU Graphs APIs for Training¶

The following section describes the usage of HPU Graph APIs in a training model.

Capture and Replay Training¶

These are the APIs for manually capturing and replaying HPU Graphs. The capture phase involves recording all the forward and backward passes, then, replaying it again and again in the actual training phase. An optional warmup phase may be added before capture phase.

Basic API usage:

Create a HPUGraph instance.
Create placeholders for input and target. These have to be compliant with batch_size and input / target dimensions.
Capture graph by wrapping the required portion of training step in HPUGraph ContextManager in first pass. Alternatively, HPUGraph.capture_begin() and HPUGraph.capture_end() can be used to wrap the module. A warmup pass may be used before capture begins.
Finally replay the graph for remaining iterations.

class HPUGraphsModel(LightningModule):
    def __init__(self, batch_size=_batch_size):
        """init"""
        super().__init__()
        # Create a HPUGraph instance
        self.g = htcore.hpu.HPUGraph()
        # Placeholders for capture. Should be compliant with data and target dims
        self.static_input = torch.rand(device="hpu")
        self.static_target = torch.rand(device="hpu")
        # result is available in static_loss tensor after graph is replayed
        self.static_loss = None
        # Set manual optimization training
        self.automatic_optimization = False
        self.training_step = self.train_with_capture_and_replay

    def train_with_capture_and_replay(self, batch, batch_idx):
        """Manual optimization training step"""
        if batch_idx == 0 and self.current_epoch == 0:
            optimizer.zero_grad(set_to_none=True)
            # Capture graphs using HPUGraph ContextManager.
            # Alternatively, use HPUGraph.capture_begin() and HPUGraph.capture_end()
            with htcore.hpu.graph(self.g):
                static_y_pred = self(self.static_input)
                self.static_loss = F.cross_entropy(static_y_pred, self.static_target)
                self.static_loss.backward()
                optimizer.step()
                return self.static_loss
        else:
            # Replay the graph
            # data must be copied to existing tensors that were used in the capture phase
            data, target = batch
            self.static_input.copy_(data)
            self.static_target.copy_(target)
            self.g.replay()
            self.log("train_loss", self.static_loss)
            return self.static_loss

make_graphed_callables¶

The make_graphed_callables API can be used to wrap a module into a standalone graph. It accepts a callable module, sample_args, and warmup steps as inputs. This API also requires the model to have only tuples for tensors as input and output. This is incompatible with workloads using data structures such as dicts and lists.

# model and sample_args as input to make_graphed_callables.
model = HPUGraphsModel().to(torch.device("hpu"))
x = torch.randn()
model = htcore.hpu.make_graphed_callables(model, (x,))
trainer.fit(model, data_module)

ModuleCacher¶

This API provides another way of wrapping the model and handles dynamic inputs in a training model. ModuleCacher internally keeps track of whether an input shape has changed, and if so, creates a new HPU graph. ModuleCacher is the recommended method for using HPU Graphs in training. max_graphs specifies the number of graphs to cache. A larger amount will increase the number of cache hits but will result in higher memory usage.

# model is given an input to ModuleCacher.
model= HPUGraphsModel()
htcore.hpu.ModuleCacher(max_graphs)(model=model, inplace=True)
trainer.fit(model, data_module)

HPU Graphs APIs for Inference¶

The following section describes the usage of HPU Graph APIs in an inference model.

Capture and Replay Inference¶

The implementation is similar to Capture and Replay in training.

Create a HPUGraph instance.
Create placeholders for input, target and predictions.
Capture graph by wrapping the required portion of test / validation step in HPUGraph ContextManager in first pass.
Finally replay the graph for remaining iterations.

class HPUGraphsModel(LightningModule):
    def __init__(self, batch_size=_batch_size):
        """init"""
        super().__init__()
        # Create a HPUGraph object
        self.g = htcore.hpu.HPUGraph()
        # Placeholders for capture. Should be compliant with data and target dims
        self.static_input = torch.rand(device="hpu")
        self.static_target = torch.rand(device="hpu")
        # Placeholder to store predictions after graph is replayed
        self.static_y_pred = torch.rand(device="hpu")
        # loss is available in static_loss tensor after graph is replayed
        self.static_loss = None

    def test_step(self, batch, batch_idx):
        """Test step"""
        x, y = batch
        if batch_idx == 0:
            with htcore.hpu.graph(self.g):
                static_y_pred = self.forward(self.static_input)
                self.static_loss = F.cross_entropy(static_y_pred, self.static_target)
        else:
            self.static_input.copy_(x)
            self.static_target.copy_(y)
            self.g.replay()

wrap_in_hpu_graph¶

This is an alternative to manual capturing and replaying HPU Graphs. htorch.hpu.wrap_in_hpu_graph can be used to wrap module forward function with HPU Graphs. This wrapper captures, caches and replays the graph. Setting disasble_tensor_cache to True will release cached output tensor memory after every replay. asynchronous specifies whether the graph capture and replay should be asynchronous.

model = NetHPUGraphs(mode=mode).to(torch.device("hpu"))
model =  htcore.hpu.wrap_in_hpu_graph(model, asynchronous=False, disable_tensor_cache=True)
trainer.test(model, data_module)

HPU Graphs and Dynamicity in Models¶

Dynamicity, resulting from changing input shapes or dynamic ops, can lead to multiple recompilations, causing longer training time and reducing performance.

HPU Graphs do not support dynamicity in models. ModuleCacher can handle dynamic inputs automatically, but it does not handle dynamic control flow and dynamic ops.

However, one can split the module into static and dynamic portions and use HPU Graphs in static regions.

For further details, refer to Dynamicity in Models

Dynamic Control Flow¶

When dynamic control flow is present, the model needs to be separated into different HPU Graphs. In the example below, the output of module1 feeds module2 or module3 depending on the dynamic control flow.

class HPUGraphsModel(LightningModule):
    def __init__(self, mode=None, batch_size=None):
        """init"""
        super(NetHPUGraphs, self).__init__()
        # Break Model into separate HPU Graphs for each control flow.
        self.module1 = NetHPUGraphs()
        self.module2 = nn.Identity()
        self.module3 = nn.ReLU()
        htcore.hpu.ModuleCacher(max_graphs)(model=self.module1, inplace=True)
        htcore.hpu.ModuleCacher(max_graphs)(model=self.module2, inplace=True)
        htcore.hpu.ModuleCacher(max_graphs)(model=self.module3, inplace=True)
        self.automatic_optimization = False
        self.training_step = self.dynamic_control_flow_training_step

    def dynamic_control_flow_training_step(self, batch, batch_idx):
        """Training step with HPU Graphs and Dynamic control flow"""
        optimizer = self.optimizers()
        data, target = batch
        optimizer.zero_grad(set_to_none=True)
        # Train with HPU Graph
        tmp = self.module1(data)

        # dynamic control flow
        if random.random() > 0.5:
            tmp = self.module2(tmp)  # forward ops run as a graph
        else:
            tmp = self.module3(tmp)  # forward ops run as a graph

        loss = F.cross_entropy(tmp, target)
        loss.backward()
        optimizer.step()
        self.log("train_loss", loss)
        return loss

Dynamic Ops¶

In this example we have module1 -> dynamic boolean indexing -> module2. Thus, both the static modules are placed into separate ModuleCacher and the dynamic op part is left out.

class HPUGraphsModel(LightningModule):
    def __init__(self, mode=None, batch_size=None):
        """init"""
        super(NetHPUGraphs, self).__init__()
        # Encapsulate dynamic ops between two separate HPU Graph modules,
        # instead of using one single HPU Graph for whole model
        self.module1 = NetHPUGraphs()
        self.module2 = nn.Identity()
        htcore.hpu.ModuleCacher(max_graphs)(model=self.module1, inplace=True)
        htcore.hpu.ModuleCacher(max_graphs)(model=self.module2, inplace=True)
        self.automatic_optimization = False
        self.training_step = self.dynamic_ops_training_step

    def dynamic_ops_training_step(self, batch, batch_idx):
        """Training step with HPU Graphs and Dynamic ops"""
        optimizer = self.optimizers()
        data, target = batch
        optimizer.zero_grad(set_to_none=True)
        # Train with HPU graph module
        tmp = self.module1(data)

        # Dynamic op
        htcore.mark_step()
        tmp = tmp[torch.where(tmp < 0)]
        htcore.mark_step()

        # Resume training with HPU graph module
        tmp = self.module2(tmp)
        loss = F.cross_entropy(tmp, target)
        loss.backward()
        optimizer.step()
        self.log("train_loss", loss)
        return loss

Limitations of HPU Graphs¶

Using HPU Graphs with torch.compile is not supported.

Please refer to Limitations of HPU Graphs