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pcdet/utils/commu_utils.py

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+"""
+This file contains primitives for multi-gpu communication.
+This is useful when doing distributed training.
+
+deeply borrow from maskrcnn-benchmark and ST3D
+"""
+
+import pickle
+import time
+
+import torch
+import torch.distributed as dist
+
+
+def get_world_size():
+    if not dist.is_available():
+        return 1
+    if not dist.is_initialized():
+        return 1
+    return dist.get_world_size()
+
+
+def get_rank():
+    if not dist.is_available():
+        return 0
+    if not dist.is_initialized():
+        return 0
+    return dist.get_rank()
+
+
+def is_main_process():
+    return get_rank() == 0
+
+
+def synchronize():
+    """
+    Helper function to synchronize (barrier) among all processes when
+    using distributed training
+    """
+    if not dist.is_available():
+        return
+    if not dist.is_initialized():
+        return
+    world_size = dist.get_world_size()
+    if world_size == 1:
+        return
+    dist.barrier()
+
+
+def all_gather(data):
+    """
+    Run all_gather on arbitrary picklable data (not necessarily tensors)
+    Args:
+        data: any picklable object
+    Returns:
+        list[data]: list of data gathered from each rank
+    """
+    world_size = get_world_size()
+    if world_size == 1:
+        return [data]
+
+    # serialized to a Tensor
+    origin_size = None
+    if not isinstance(data, torch.Tensor):
+        buffer = pickle.dumps(data)
+        storage = torch.ByteStorage.from_buffer(buffer)
+        tensor = torch.ByteTensor(storage).to("cuda")
+    else:
+        origin_size = data.size()
+        tensor = data.reshape(-1)
+
+    tensor_type = tensor.dtype
+
+    # obtain Tensor size of each rank
+    local_size = torch.LongTensor([tensor.numel()]).to("cuda")
+    size_list = [torch.LongTensor([0]).to("cuda") for _ in range(world_size)]
+    dist.all_gather(size_list, local_size)
+    size_list = [int(size.item()) for size in size_list]
+    max_size = max(size_list)
+
+    # receiving Tensor from all ranks
+    # we pad the tensor because torch all_gather does not support
+    # gathering tensors of different shapes
+    tensor_list = []
+    for _ in size_list:
+        tensor_list.append(torch.FloatTensor(size=(max_size,)).cuda().to(tensor_type))
+    if local_size != max_size:
+        padding = torch.FloatTensor(size=(max_size - local_size,)).cuda().to(tensor_type)
+        tensor = torch.cat((tensor, padding), dim=0)
+    dist.all_gather(tensor_list, tensor)
+
+    data_list = []
+    for size, tensor in zip(size_list, tensor_list):
+        if origin_size is None:
+            buffer = tensor.cpu().numpy().tobytes()[:size]
+            data_list.append(pickle.loads(buffer))
+        else:
+            buffer = tensor[:size]
+            data_list.append(buffer)
+
+    if origin_size is not None:
+        new_shape = [-1] + list(origin_size[1:])
+        resized_list = []
+        for data in data_list:
+            # suppose the difference of tensor size exist in first dimension
+            data = data.reshape(new_shape)
+            resized_list.append(data)
+
+        return resized_list
+    else:
+        return data_list
+
+
+def reduce_dict(input_dict, average=True):
+    """
+    Args:
+        input_dict (dict): all the values will be reduced
+        average (bool): whether to do average or sum
+    Reduce the values in the dictionary from all processes so that process with rank
+    0 has the averaged results. Returns a dict with the same fields as
+    input_dict, after reduction.
+    """
+    world_size = get_world_size()
+    if world_size < 2:
+        return input_dict
+    with torch.no_grad():
+        names = []
+        values = []
+        # sort the keys so that they are consistent across processes
+        for k in sorted(input_dict.keys()):
+            names.append(k)
+            values.append(input_dict[k])
+        values = torch.stack(values, dim=0)
+        dist.reduce(values, dst=0)
+        if dist.get_rank() == 0 and average:
+            # only main process gets accumulated, so only divide by
+            # world_size in this case
+            values /= world_size
+        reduced_dict = {k: v for k, v in zip(names, values)}
+    return reduced_dict
+
+
+def average_reduce_value(data):
+    data_list = all_gather(data)
+    return sum(data_list) / len(data_list)
+
+
+def all_reduce(data, op="sum", average=False):
+
+    def op_map(op):
+        op_dict = {
+            "SUM": dist.ReduceOp.SUM,
+            "MAX": dist.ReduceOp.MAX,
+            "MIN": dist.ReduceOp.MIN,
+            "PRODUCT": dist.ReduceOp.PRODUCT,
+        }
+        return op_dict[op]
+
+    world_size = get_world_size()
+    if world_size > 1:
+        reduced_data = data.clone()
+        dist.all_reduce(reduced_data, op=op_map(op.upper()))
+        if average:
+            assert op.upper() == 'SUM'
+            return reduced_data / world_size
+        else:
+            return reduced_data
+    return data
+
+
+@torch.no_grad()
+def concat_all_gather(tensor):
+    """
+    Performs all_gather operation on the provided tensors.
+    *** Warning ***: torch.distributed.all_gather has no gradient.
+    """
+    tensors_gather = [torch.ones_like(tensor)
+        for _ in range(torch.distributed.get_world_size())]
+    torch.distributed.all_gather(tensors_gather, tensor, async_op=False)
+
+    output = torch.cat(tensors_gather, dim=0)
+    return output