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Argonne Leadership Computing Facility

CosmicTagger Conversion

The intent of this page is to show conceptually how to convert a model to run on the Graphcore system. It is not necessary to convert CosmicTagger because it has already been converted and is located at CosmicTagger on the Graphcore branch. The original is located at CosmicTagger.

Run Model on CPU

The first step to converting a model is to verify that it runs on the CPU. This step has been verified for CosmicTagger.

Config.py

CosmicTagger can run on multiple machines. As such, it is necessary to specify the architecture that one is using. For example, CPU or GPU. The architecture is stored in the ComputeMode class.

Edit src/config/config.py. Add IPU to the ComputeMode class.

class ComputeMode(Enum):
    CPU   = 0
    #...
    IPU   = 5

Trainer.py

Edit src/utils/torch/trainer.py.

Import PopTorch

PopTorch is Graphcore's extension of PyTorch.

Import poptorch at the top of the file.

import poptorch

Wrap Model

Wrap the model using poptorch.trainingModel() so that it may be ran on IPUs for training.

Wrap the model using poptorch.inferenceModel() when not training.

Find the following code around line 90 in the init_network method.

        # Foregoing any fusions as to not disturb the existing ingestion pipeline
        if self.is_training() and self.args.mode.quantization_aware:
            self._raw_net.qconfig = torch.quantization.get_default_qat_qconfig('fbgemm')
            self._net = torch.quantization.prepare_qat(self._raw_net)
        else:
            self._net = self._raw_net

After the above code, add:

        if self.args.run.compute_mode == ComputeMode.IPU:
            if self.is_training():
                opts = poptorch.Options()
                self._net = poptorch.trainingModel(self._net, opts, optimizer=torch.optim.SGD(self._net.parameters(), lr=1e-3))
            else:
                self._net = poptorch.inferenceModel(self._net)

See poptorch.trainingModel() and poptorch.inferenceModel() for more information.

There is also a Build the Model tutorial.

Update Optimizer

Update init_optimizer() to use the poptorch class instead of the torch class as needed.

Change:

        if self.args.mode.optimizer.name == OptimizerKind.rmsprop:
            self._opt = torch.optim.RMSprop(self._net.parameters(), 1.0, eps=1e-4)
        else:
            self._opt = torch.optim.Adam(self._net.parameters(), 1.0)

to:

        if self.args.mode.optimizer.name == OptimizerKind.rmsprop:
            if self.args.run.compute_mode == ComputeMode.IPU:
                self._opt = poptorch.optim.RMSprop(self._net.parameters(), 1.0, eps=1e-4)
            else:
                self._opt = torch.optim.RMSprop(self._net.parameters(), 1.0, eps=1e-4)
        else:
            if self.args.run.compute_mode == ComputeMode.IPU:
                self._opt = poptorch.optim.Adam(self._net.parameters(), 1.0)
            else:
                self._opt = torch.optim.Adam(self._net.parameters(), 1.0)

Update the Forward Pass

Putting the loss calculation in forward_pass() allows the loss computation to be performed on the IPUs. This will be faster because the data will not need to be transfered round-trip to the CPU.

Change forward_pass():

Original

            if net is None:
                logits_image = self._net(minibatch_data['image'])
            else:
                logits_image = net(minibatch_data['image'])

Updated

The following code changes are to account for the loss function, i.e., self.loss_calculator, and the image labels, i.e., labels_image, to be passed to the model's forward_pass method. Additionally, the calculated loss is returned from the forward_pass method.

            if net is None:
                if self.args.run.compute_mode == ComputeMode.IPU:
                    logits_image, labels_image, loss = self._net(minibatch_data['image'], self.loss_calculator, labels_image)
                    return logits_image, labels_image, loss
                else:
                    logits_image = self._net(minibatch_data['image'])
            else:
                if self.args.run.compute_mode == ComputeMode.IPU and self.args.mode.name != ModeKind.inference:
                    logits_image, labels_image, loss = net(minibatch_data['image'], self.loss_calculator, labels_image)
                    return logits_image, labels_image, loss
                else:
                    logits_image = net(minibatch_data['image'])

Update the Training Step

Receive the extra loss variable from the forward_pass method.

Update the train_step method.

Original Training Step

                    with self.timing_context("forward"):
                        if self.args.run.precision == Precision.mixed and self.args.run.compute_mode == ComputeMode.GPU:
                            with torch.cuda.amp.autocast():
                                logits_image, labels_image = self.forward_pass(minibatch_data)
                        else:
                            logits_image, labels_image = self.forward_pass(minibatch_data)

                    verbose = False

                    # Compute the loss based on the logits
                    with self.timing_context("loss"):
                        loss = self.loss_calculator(labels_image, logits_image)

Updated Training Step

The forward_pass() method was changed to return the extra variable loss in the previous section. It is now received conditionally when using an IPU(s).

In the with self.timing_context("loss"): section, only calculate loss if not using an IPU(s).

                    with self.timing_context("forward"):
                        if self.args.run.precision == Precision.mixed and self.args.run.compute_mode == ComputeMode.GPU:
                            with torch.cuda.amp.autocast():
                                logits_image, labels_image = self.forward_pass(minibatch_data)
                        else:
                            if self.args.run.compute_mode == ComputeMode.IPU:
                                logits_image, labels_image, loss = self.forward_pass(minibatch_data)
                            else:
                                logits_image, labels_image = self.forward_pass(minibatch_data)

                    verbose = False


                    # Compute the loss based on the logits
                    with self.timing_context("loss"):
                        if self.args.run.compute_mode == ComputeMode.IPU:
                            loss = loss
                        else:
                            loss = self.loss_calculator(labels_image, logits_image)

Update Validation Step

Update the val_step method.

Original Validation Step Code

Find this code.

            if self.args.run.precision == Precision.mixed and self.args.run.compute_mode == ComputeMode.GPU:
                with torch.cuda.amp.autocast():
                    logits_image, labels_image = self.forward_pass(minibatch_data, net=val_net)
            else:
                logits_image, labels_image = self.forward_pass(minibatch_data, net=val_net)

            # Compute the loss based on the logits
            loss = self.loss_calculator(labels_image, logits_image)

Updated Validation Step Code

Change the code to the following.

            if self.args.run.precision == Precision.mixed and self.args.run.compute_mode == ComputeMode.GPU:
                with torch.cuda.amp.autocast():
                    logits_image, labels_image = self.forward_pass(minibatch_data, net=val_net)

                    # Compute the loss based on the logits
                    loss = self.loss_calculator(labels_image, logits_image)
            else:
                if self.args.run.compute_mode == ComputeMode.IPU:
                    logits_image, labels_image, loss = self.forward_pass(minibatch_data, net=val_net)
                else:
                    logits_image, labels_image = self.forward_pass(minibatch_data, net=val_net)

                    # Compute the loss based on the logits
                    loss = self.loss_calculator(labels_image, logits_image)

UResNet2D Model

Update Model

The Graphcore system is more computationally efficient if the loss function is on the IPU. This is accomplished by using the loss function within the model's forward method.

Edit src/networks/torch/uresnet2D.py.

Update the Forward Declaration

Find the forward method.

def forward(self, input_tensor):

Update the argument list to include the loss function, i.e., loss_calculator and the image labels, i.e., labels_image.

def forward(self, input_tensor, loss_calculator=None, labels_image=None):

Add Loss Calculation

Add the loss calculation just before the forward method returns.

        if loss_calculator is not None:

            labels_image = labels_image.long()
            labels_image = torch.chunk(labels_image, chunks=3, dim=1)
            shape =  labels_image[0].shape
            labels_image = [ _label.view([shape[0], shape[-2], shape[-1]]) for _label in labels_image ]

            loss = loss_calculator(labels_image, x)
            import poptorch
            loss = poptorch.identity_loss(loss , reduction="mean")
            return x, labels_image, loss

        # This return already exists.
        return x

The poptorch.identity_loss method takes a single PyTorch tensor and will backpropagate a gradient of ones through it. You may find an example at here

bin/exec.py

The following is included for completeness. One will not likely find this in other code.

Open bin/exec.py in your favorite editor. Change:

@hydra.main(version_base=None, config_path="../src/config", config_name="config")

to

@hydra.main(config_path="../src/config", config_name="config")