def multi_gpu_test(model, data_loader, tmpdir=None, gpu_collect=False):
    """Test model with multiple gpus.

    This method tests model with multiple gpus and collects the results
    under two different modes: gpu and cpu modes. By setting
    ``gpu_collect=True``, it encodes results to gpu tensors and use gpu
    communication for results collection. On cpu mode it saves the results on
    different gpus to ``tmpdir`` and collects them by the rank 0 worker.

    Args:
        model (nn.Module): Model to be tested.
        data_loader (nn.Dataloader): Pytorch data loader.
        tmpdir (str): Path of directory to save the temporary results from
            different gpus under cpu mode.
        gpu_collect (bool): Option to use either gpu or cpu to collect results.

    Returns:
        list: The prediction results.
    """
    model.eval()
    results = []
    dataset = data_loader.dataset
    rank, world_size = get_dist_info()
    if rank == 0:
        prog_bar = mmcv.ProgressBar(len(dataset))
    time.sleep(2)  # This line can prevent deadlock problem in some cases.
    for i, data in enumerate(data_loader):
        with torch.no_grad():
            result = model(return_loss=False, **data)
        results.extend(result)

        if rank == 0:
            batch_size = len(result)
            batch_size_all = batch_size * world_size
            if batch_size_all + prog_bar.completed > len(dataset):
                batch_size_all = len(dataset) - prog_bar.completed
            for _ in range(batch_size_all):
                prog_bar.update()

    # collect results from all ranks
    if gpu_collect:
        results = collect_results_gpu(results, len(dataset))
    else:
        results = collect_results_cpu(results, len(dataset), tmpdir)
    return results
Test model with multiple gpus.

    This method tests model with multiple gpus and collects the results
    under two different modes: gpu and cpu modes. By setting
    ``gpu_collect=True``, it encodes results to gpu tensors and use gpu
    communication for results collection. On cpu mode it saves the results on
    different gpus to ``tmpdir`` and collects them by the rank 0 worker.

    Args:
        model (nn.Module): Model to be tested.
        data_loader (nn.Dataloader): Pytorch data loader.
        tmpdir (str): Path of directory to save the temporary results from
            different gpus under cpu mode.
        gpu_collect (bool): Option to use either gpu or cpu to collect results.

    Returns:
        list: The prediction results.
    
ControlNet-v1-1-nightly/annotator/uniformer/mmcv/engine/test.py