tools/handobj/train_net.py [118:260]:
- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
        loss = 0
        for key in extra_loss.keys():
            if "loss" in key:
                loss += extra_loss[key]

        # check Nan Loss.
        misc.check_nan_losses(loss)

        # Perform the backward pass.
        optimizer.zero_grad()
        loss.backward()
        # Update the parameters.
        optimizer.step()

        if cfg.DETECTION.ENABLE:
            if cfg.NUM_GPUS > 1:
                loss = du.all_reduce([loss])[0]
            loss = loss.item()

            train_meter.iter_toc()
            # Update and log stats.
            train_meter.update_stats(None, None, None, loss, lr)
            # write to tensorboard format if available.
            if writer is not None:
                writer.add_scalars(
                    {"Train/loss": loss, "Train/lr": lr},
                    global_step=data_size * cur_epoch + cur_iter,
                )

        else:
            top1_err, top5_err = None, None
            if cfg.DATA.MULTI_LABEL:
                # Gather all the predictions across all the devices.
                if cfg.NUM_GPUS > 1:
                    [loss] = du.all_reduce([loss])
                    for key in extra_loss.keys():
                        extra_loss[key] = du.all_reduce([extra_loss[key]])[0]
                loss = loss.item()
                for key in extra_loss.keys():
                    extra_loss[key] = extra_loss[key].item()
            else:
                # Compute the errors.
                ks = (1, 5) if cfg.MODEL.NUM_CLASSES >= 5 else (1, 1)
                num_topks_correct = metrics.topks_correct(preds, labels, ks)
                top1_err, top5_err = [
                    (1.0 - x / preds.size(0)) * 100.0 for x in num_topks_correct
                ]

                # Gather all the predictions across all the devices.
                if cfg.NUM_GPUS > 1:
                    loss, top1_err, top5_err = du.all_reduce(
                        [loss, top1_err, top5_err]
                    )
                    for key in extra_loss.keys():
                        extra_loss[key] = du.all_reduce([extra_loss[key]])[0]


                # Copy the stats from GPU to CPU (sync point).
                loss, top1_err, top5_err = (
                    loss.item(),
                    top1_err.item(),
                    top5_err.item(),
                )
                for key in extra_loss.keys():
                    extra_loss[key] = extra_loss[key].item()


            train_meter.iter_toc()
            # Update and log stats.
            train_meter.update_stats(
                top1_err, top5_err, loss, lr, inputs[0].size(0) * cfg.NUM_GPUS, stats=extra_loss,
            )
            # write to tensorboard format if available.
            if writer is not None:
                writer.add_scalars(
                    {
                        "Train/loss": loss,
                        "Train/lr": lr,
                        "Train/Top1_err": top1_err,
                        "Train/Top5_err": top5_err,
                    },
                    global_step=data_size * cur_epoch + cur_iter,
                )

        train_meter.log_iter_stats(cur_epoch, cur_iter)
        train_meter.iter_tic()
    # Log epoch stats.
    train_meter.log_epoch_stats(cur_epoch)
    train_meter.reset()


@torch.no_grad()
def eval_epoch(val_loader, model, val_meter, cur_epoch, cfg, writer=None):
    """
    Evaluate the model on the val set.
    Args:
        val_loader (loader): data loader to provide validation data.
        model (model): model to evaluate the performance.
        val_meter (ValMeter): meter instance to record and calculate the metrics.
        cur_epoch (int): number of the current epoch of training.
        cfg (CfgNode): configs. Details can be found in
            slowfast/config/defaults.py
        writer (TensorboardWriter, optional): TensorboardWriter object
            to writer Tensorboard log.
    """

    # Evaluation mode enabled. The running stats would not be updated.
    model.eval()
    val_meter.iter_tic()

    for cur_iter, (inputs, labels, _, meta) in enumerate(val_loader):
        # Transferthe data to the current GPU device.
        if isinstance(inputs, (list,)):
            for i in range(len(inputs)):
                inputs[i] = inputs[i].cuda(non_blocking=True)
        else:
            inputs = inputs.cuda(non_blocking=True)
        labels = labels.cuda()
        for key, val in meta.items():
            if isinstance(val, (list,)):
                for i in range(len(val)):
                    val[i] = val[i].cuda(non_blocking=True)
            else:
                meta[key] = val.cuda(non_blocking=True)

        if cfg.DETECTION.ENABLE:
            # Compute the predictions.
            preds = model(inputs, meta["boxes"])

            preds = preds.cpu()
            ori_boxes = meta["ori_boxes"].cpu()
            metadata = meta["metadata"].cpu()

            if cfg.NUM_GPUS > 1:
                preds = torch.cat(du.all_gather_unaligned(preds), dim=0)
                ori_boxes = torch.cat(du.all_gather_unaligned(ori_boxes), dim=0)
                metadata = torch.cat(du.all_gather_unaligned(metadata), dim=0)

            val_meter.iter_toc()
            # Update and log stats.
            val_meter.update_stats(preds.cpu(), ori_boxes.cpu(), metadata.cpu())

        else:
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tools/kd/train_net.py [111:254]:
- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
        loss = 0
        for key in extra_loss.keys():
            if "loss" in key:
                loss += extra_loss[key]

        # check Nan Loss.
        misc.check_nan_losses(loss)

        # Perform the backward pass.
        optimizer.zero_grad()
        loss.backward()
        # Update the parameters.
        optimizer.step()

        if cfg.DETECTION.ENABLE:
            if cfg.NUM_GPUS > 1:
                loss = du.all_reduce([loss])[0]
            loss = loss.item()

            train_meter.iter_toc()
            # Update and log stats.
            train_meter.update_stats(None, None, None, loss, lr)
            # write to tensorboard format if available.
            if writer is not None:
                writer.add_scalars(
                    {"Train/loss": loss, "Train/lr": lr},
                    global_step=data_size * cur_epoch + cur_iter,
                )

        else:
            top1_err, top5_err = None, None
            if cfg.DATA.MULTI_LABEL:
                # Gather all the predictions across all the devices.
                if cfg.NUM_GPUS > 1:
                    [loss] = du.all_reduce([loss])
                    for key in extra_loss.keys():
                        extra_loss[key] = du.all_reduce([extra_loss[key]])[0]
                loss = loss.item()
                for key in extra_loss.keys():
                    extra_loss[key] = extra_loss[key].item()
            else:
                # Compute the errors.
                ks = (1, 5) if cfg.MODEL.NUM_CLASSES >= 5 else (1, 1)
                num_topks_correct = metrics.topks_correct(preds, labels, ks)
                top1_err, top5_err = [
                    (1.0 - x / preds.size(0)) * 100.0 for x in num_topks_correct
                ]

                # Gather all the predictions across all the devices.
                if cfg.NUM_GPUS > 1:
                    loss, top1_err, top5_err = du.all_reduce(
                        [loss, top1_err, top5_err]
                    )
                    for key in extra_loss.keys():
                        extra_loss[key] = du.all_reduce([extra_loss[key]])[0]


                # Copy the stats from GPU to CPU (sync point).
                loss, top1_err, top5_err = (
                    loss.item(),
                    top1_err.item(),
                    top5_err.item(),
                )
                for key in extra_loss.keys():
                    extra_loss[key] = extra_loss[key].item()


            train_meter.iter_toc()
            # Update and log stats.
            train_meter.update_stats(
                top1_err, top5_err, loss, lr, inputs[0].size(0) * cfg.NUM_GPUS, stats=extra_loss,
            )
            # write to tensorboard format if available.
            if writer is not None:
                writer.add_scalars(
                    {
                        "Train/loss": loss,
                        "Train/lr": lr,
                        "Train/Top1_err": top1_err,
                        "Train/Top5_err": top5_err,
                    },
                    global_step=data_size * cur_epoch + cur_iter,
                )

        train_meter.log_iter_stats(cur_epoch, cur_iter)
        train_meter.iter_tic()

    # Log epoch stats.
    train_meter.log_epoch_stats(cur_epoch)
    train_meter.reset()


@torch.no_grad()
def eval_epoch(val_loader, model, val_meter, cur_epoch, cfg, writer=None):
    """
    Evaluate the model on the val set.
    Args:
        val_loader (loader): data loader to provide validation data.
        model (model): model to evaluate the performance.
        val_meter (ValMeter): meter instance to record and calculate the metrics.
        cur_epoch (int): number of the current epoch of training.
        cfg (CfgNode): configs. Details can be found in
            slowfast/config/defaults.py
        writer (TensorboardWriter, optional): TensorboardWriter object
            to writer Tensorboard log.
    """

    # Evaluation mode enabled. The running stats would not be updated.
    model.eval()
    val_meter.iter_tic()

    for cur_iter, (inputs, labels, _, meta) in enumerate(val_loader):
        # Transferthe data to the current GPU device.
        if isinstance(inputs, (list,)):
            for i in range(len(inputs)):
                inputs[i] = inputs[i].cuda(non_blocking=True)
        else:
            inputs = inputs.cuda(non_blocking=True)
        labels = labels.cuda()
        for key, val in meta.items():
            if isinstance(val, (list,)):
                for i in range(len(val)):
                    val[i] = val[i].cuda(non_blocking=True)
            else:
                meta[key] = val.cuda(non_blocking=True)

        if cfg.DETECTION.ENABLE:
            # Compute the predictions.
            preds = model(inputs, meta["boxes"])

            preds = preds.cpu()
            ori_boxes = meta["ori_boxes"].cpu()
            metadata = meta["metadata"].cpu()

            if cfg.NUM_GPUS > 1:
                preds = torch.cat(du.all_gather_unaligned(preds), dim=0)
                ori_boxes = torch.cat(du.all_gather_unaligned(ori_boxes), dim=0)
                metadata = torch.cat(du.all_gather_unaligned(metadata), dim=0)

            val_meter.iter_toc()
            # Update and log stats.
            val_meter.update_stats(preds.cpu(), ori_boxes.cpu(), metadata.cpu())

        else:
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