test_torch.py

# Copyright 2018 Uber Technologies, Inc. All Rights Reserved.
#
# Licensed under the Apache License, Version 2.0 (the "License");
# you may not use this file except in compliance with the License.
# You may obtain a copy of the License at
#
#     http://www.apache.org/licenses/LICENSE-2.0
#
# Unless required by applicable law or agreed to in writing, software
# distributed under the License is distributed on an "AS IS" BASIS,
# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
# See the License for the specific language governing permissions and
# limitations under the License.
# ==============================================================================

from __future__ import absolute_import
from __future__ import division
from __future__ import print_function

from distutils.version import LooseVersion
import inspect
import itertools
import numpy as np
import os
import tempfile
import torch
import torch.nn.functional as F
import unittest

import horovod.torch as hvd

from common import mpi_env_rank_and_size

_fp16_supported = LooseVersion(torch.__version__) >= LooseVersion('1.0.0')


class TorchTests(unittest.TestCase):
    """
    Tests for ops in horovod.torch.
    """

    def test_horovod_rank(self):
        """Test that the rank returned by hvd.rank() is correct."""
        true_rank, _ = mpi_env_rank_and_size()
        hvd.init()
        rank = hvd.rank()
        assert true_rank == rank

    def test_horovod_size(self):
        """Test that the size returned by hvd.size() is correct."""
        _, true_size = mpi_env_rank_and_size()
        hvd.init()
        size = hvd.size()
        assert true_size == size

    def test_horovod_allreduce(self):
        """Test that the allreduce correctly sums 1D, 2D, 3D tensors."""
        hvd.init()
        size = hvd.size()
        dtypes = [torch.IntTensor, torch.LongTensor,
                  torch.FloatTensor, torch.DoubleTensor]
        if torch.cuda.is_available():
            dtypes += [torch.cuda.IntTensor, torch.cuda.LongTensor,
                       torch.cuda.FloatTensor, torch.cuda.DoubleTensor]
            if _fp16_supported:
                dtypes += [torch.cuda.HalfTensor]
        dims = [1, 2, 3]
        for dtype, dim in itertools.product(dtypes, dims):
            torch.manual_seed(1234)
            tensor = torch.FloatTensor(*([17] * dim)).random_(-100, 100)
            tensor = tensor.type(dtype)
            summed = hvd.allreduce(tensor, average=False)
            multiplied = tensor * size
            max_difference = summed.data.sub(multiplied).max()

            # Threshold for floating point equality depends on number of
            # ranks, since we're comparing against precise multiplication.
            if size <= 3 or dtype in [torch.IntTensor, torch.LongTensor,
                                      torch.cuda.IntTensor, torch.cuda.LongTensor]:
                threshold = 0
            elif size < 10:
                threshold = 1e-4
            elif size < 15:
                threshold = 5e-4
            else:
                break

            assert max_difference <= threshold, 'hvd.allreduce produces incorrect results'

    def test_horovod_allreduce_average(self):
        """Test that the allreduce correctly sums 1D, 2D, 3D tensors."""
        hvd.init()
        size = hvd.size()
        dtypes = [torch.IntTensor, torch.LongTensor,
                  torch.FloatTensor, torch.DoubleTensor]
        if torch.cuda.is_available():
            dtypes += [torch.cuda.IntTensor, torch.cuda.LongTensor,
                       torch.cuda.FloatTensor, torch.cuda.DoubleTensor]
            if _fp16_supported:
                dtypes += [torch.cuda.HalfTensor]
        dims = [1, 2, 3]
        for dtype, dim in itertools.product(dtypes, dims):
            torch.manual_seed(1234)
            tensor = torch.FloatTensor(*([17] * dim)).random_(-100, 100)
            tensor = tensor.type(dtype)
            averaged = hvd.allreduce(tensor, average=True)
            max_difference = averaged.data.sub(tensor).max()

            # Threshold for floating point equality depends on number of
            # ranks, since we're comparing against precise multiplication.
            if size <= 3 or dtype in [torch.IntTensor, torch.LongTensor,
                                      torch.cuda.IntTensor, torch.cuda.LongTensor]:
                threshold = 0
            elif size < 10:
                threshold = 1e-4
            elif size < 15:
                threshold = 5e-4
            else:
                break

            assert max_difference <= threshold, 'hvd.allreduce produces incorrect results'

    def test_horovod_allreduce_inplace(self):
        """Test that the allreduce correctly sums 1D, 2D, 3D tensors."""
        hvd.init()
        size = hvd.size()
        dtypes = [torch.IntTensor, torch.LongTensor,
                  torch.FloatTensor, torch.DoubleTensor]
        if torch.cuda.is_available():
            dtypes += [torch.cuda.IntTensor, torch.cuda.LongTensor,
                       torch.cuda.FloatTensor, torch.cuda.DoubleTensor]
            if _fp16_supported:
                dtypes += [torch.cuda.HalfTensor]
        dims = [1, 2, 3]
        for dtype, dim in itertools.product(dtypes, dims):
            torch.manual_seed(1234)
            tensor = torch.FloatTensor(*([17] * dim)).random_(-100, 100)
            tensor = tensor.type(dtype)
            multiplied = tensor * size
            hvd.allreduce_(tensor, average=False)
            max_difference = tensor.sub(multiplied).max()

            # Threshold for floating point equality depends on number of
            # ranks, since we're comparing against precise multiplication.
            if size <= 3 or dtype in [torch.IntTensor, torch.LongTensor,
                                      torch.cuda.IntTensor, torch.cuda.LongTensor]:
                threshold = 0
            elif size < 10:
                threshold = 1e-4
            elif size < 15:
                threshold = 5e-4
            else:
                break

            assert max_difference <= threshold, 'hvd.allreduce produces incorrect results'

    def test_horovod_allreduce_async_fused(self):
        """Test that the allreduce correctly sums 1D, 2D, 3D tensors
        with Tensor Fusion."""
        hvd.init()
        size = hvd.size()
        dtypes = [torch.IntTensor, torch.LongTensor,
                  torch.FloatTensor, torch.DoubleTensor]
        if torch.cuda.is_available():
            dtypes += [torch.cuda.IntTensor, torch.cuda.LongTensor,
                       torch.cuda.FloatTensor, torch.cuda.DoubleTensor]
            if _fp16_supported:
                dtypes += [torch.cuda.HalfTensor]
        dims = [1, 2, 3]
        tests = []
        is_hvd_poll_false_once = False
        for dtype, dim in itertools.product(dtypes, dims):
            torch.manual_seed(1234)
            tensor = torch.FloatTensor(*([17] * dim)).random_(-100, 100)
            tensor = tensor.type(dtype)
            handle = hvd.allreduce_async(tensor, average=False)
            if not hvd.poll(handle):
                is_hvd_poll_false_once = True
            multiplied = tensor * size
            tests.append((dtype, multiplied, handle))

        # Make sure it's an asynchronous operation.
        assert is_hvd_poll_false_once, 'hvd.poll() always returns True, not an async op?'

        for dtype, multiplied, handle in tests:
            summed = hvd.synchronize(handle)
            max_difference = summed.sub(multiplied).max()

            # Threshold for floating point equality depends on number of
            # ranks, since we're comparing against precise multiplication.
            if size <= 3 or dtype in [torch.IntTensor, torch.LongTensor,
                                      torch.cuda.IntTensor, torch.cuda.LongTensor]:
                threshold = 0
            elif size < 10:
                threshold = 1e-4
            elif size < 15:
                threshold = 5e-4
            else:
                break

            assert max_difference <= threshold, 'hvd.allreduce produces incorrect results'

    def test_horovod_allreduce_multi_gpu(self):
        """Test that the allreduce works on multiple GPUs."""
        # Only do this test if there are GPUs available.
        if not torch.cuda.is_available():
            return

        hvd.init()
        local_rank = hvd.local_rank()
        size = hvd.size()

        iter = 0
        dtypes = [torch.cuda.IntTensor, torch.cuda.LongTensor,
                  torch.cuda.FloatTensor, torch.cuda.DoubleTensor]
        if _fp16_supported:
            dtypes += [torch.cuda.HalfTensor]

        dims = [1, 2, 3]
        for dtype, dim in itertools.product(dtypes, dims):
            iter += 1
            torch.manual_seed(1234)
            tensor = torch.FloatTensor(*([17] * dim)).random_(-100, 100)
            device = local_rank * 2 + (iter + local_rank) % 2
            tensor = tensor.cuda(device).type(dtype)
            multiplied = tensor * size
            hvd.allreduce_(tensor, average=False)
            max_difference = tensor.sub(multiplied).max()

            # Threshold for floating point equality depends on number of
            # ranks, since we're comparing against precise multiplication.
            if size <= 3 or dtype in [torch.cuda.IntTensor, torch.cuda.LongTensor]:
                threshold = 0
            elif size < 10:
                threshold = 1e-4
            elif size < 15:
                threshold = 5e-4
            else:
                break

            assert max_difference <= threshold, 'hvd.allreduce produces incorrect results'

    def test_horovod_allreduce_error(self):
        """Test that the allreduce raises an error if different ranks try to
        send tensors of different rank or dimension."""
        hvd.init()
        rank = hvd.rank()
        size = hvd.size()

        # This test does not apply if there is only one worker.
        if size == 1:
            return

        # Same rank, different dimension
        torch.manual_seed(1234)
        dims = [17 + rank] * 3
        tensor = torch.FloatTensor(*dims).random_(-100, 100)
        try:
            hvd.allreduce(tensor)
            assert False, 'hvd.allreduce did not throw error'
        except (torch.FatalError, RuntimeError):
            pass

        # Same number of elements, different rank
        torch.manual_seed(1234)
        if rank == 0:
            dims = [17, 23 * 57]
        else:
            dims = [17, 23, 57]
        tensor = torch.FloatTensor(*dims).random_(-100, 100)
        try:
            hvd.allreduce(tensor)
            assert False, 'hvd.allreduce did not throw error'
        except (torch.FatalError, RuntimeError):
            pass

    def test_horovod_allreduce_type_error(self):
        """Test that the allreduce raises an error if different ranks try to
        send tensors of different type."""
        hvd.init()
        rank = hvd.rank()
        size = hvd.size()

        # This test does not apply if there is only one worker.
        if size == 1:
            return

        # Same rank, different dimension
        dims = [17] * 3
        if rank % 2 == 0:
            tensor = torch.IntTensor(*dims)
        else:
            tensor = torch.FloatTensor(*dims)

        try:
            hvd.allreduce(tensor)
            assert False, 'hvd.allreduce did not throw error'
        except (torch.FatalError, RuntimeError):
            pass

    def test_horovod_allreduce_cpu_gpu_error(self):
        """Test that the allreduce raises an error if different ranks try to
        perform reduction on CPU and GPU."""
        # Only do this test if there are GPUs available.
        if not torch.cuda.is_available():
            return

        hvd.init()
        rank = hvd.rank()
        size = hvd.size()

        # This test does not apply if there is only one worker.
        if size == 1:
            return

        # Same rank, different dimension
        dims = [17] * 3
        if rank % 2 == 0:
            tensor = torch.cuda.FloatTensor(*dims)
        else:
            tensor = torch.FloatTensor(*dims)

        try:
            hvd.allreduce(tensor)
            assert False, 'hvd.allreduce did not throw error'
        except (torch.FatalError, RuntimeError):
            pass

    def test_horovod_allreduce_grad(self):
        """Test the correctness of the allreduce gradient."""
        hvd.init()
        size = hvd.size()
        # Only Tensors of floating point dtype can require gradients
        dtypes = [torch.FloatTensor, torch.DoubleTensor]
        if torch.cuda.is_available():
            dtypes += [torch.cuda.FloatTensor, torch.cuda.DoubleTensor]
            if _fp16_supported:
                dtypes += [torch.cuda.HalfTensor]
        dims = [1, 2, 3]
        for dtype, dim in itertools.product(dtypes, dims):
            torch.manual_seed(1234)
            tensor = torch.FloatTensor(*([17] * dim)).random_(-100, 100)
            tensor = tensor.type(dtype)
            tensor.requires_grad_()
            summed = hvd.allreduce(tensor, average=False)

            summed.backward(torch.ones([17] * dim).type(dtype))
            grad_out = tensor.grad.data.cpu().numpy()

            expected = np.ones([17] * dim) * size
            err = np.linalg.norm(expected - grad_out)
            self.assertLess(err, 0.00000001,
                            "gradient %s differs from expected %s, "
                            "error: %s" % (grad_out, expected, str(err)))

    def test_horovod_allreduce_grad_average(self):
        """Test the correctness of the allreduce averaged gradient."""
        hvd.init()
        # Only Tensors of floating point dtype can require gradients
        dtypes = [torch.FloatTensor, torch.DoubleTensor]
        if torch.cuda.is_available():
            dtypes += [torch.cuda.FloatTensor, torch.cuda.DoubleTensor]
            if _fp16_supported:
                dtypes += [torch.cuda.HalfTensor]
        dims = [1, 2, 3]
        for dtype, dim in itertools.product(dtypes, dims):
            torch.manual_seed(1234)
            tensor = torch.FloatTensor(*([17] * dim)).random_(-100, 100)
            tensor = tensor.type(dtype)
            tensor.requires_grad_()
            summed = hvd.allreduce(tensor, average=True)

            summed.backward(torch.ones([17] * dim).type(dtype))
            grad_out = tensor.grad.data.cpu().numpy()

            expected = np.ones([17] * dim)
            err = np.linalg.norm(expected - grad_out)
            self.assertLess(err, 0.00000001,
                            "gradient %s differs from expected %s, "
                            "error: %s" % (grad_out, expected, str(err)))

    def test_horovod_allgather(self):
        """Test that the allgather correctly gathers 1D, 2D, 3D tensors."""
        hvd.init()
        rank = hvd.rank()
        size = hvd.size()

        dtypes = [torch.ByteTensor, torch.CharTensor, torch.ShortTensor,
                  torch.IntTensor, torch.LongTensor, torch.FloatTensor, torch.DoubleTensor]
        if torch.cuda.is_available():
            dtypes += [torch.cuda.ByteTensor, torch.cuda.CharTensor, torch.cuda.ShortTensor,
                       torch.cuda.IntTensor, torch.cuda.LongTensor,
                       torch.cuda.FloatTensor, torch.cuda.DoubleTensor]
            if _fp16_supported:
                dtypes += [torch.cuda.HalfTensor]
        dims = [1, 2, 3]
        for dtype, dim in itertools.product(dtypes, dims):
            tensor = torch.FloatTensor(*([17] * dim)).fill_(1).mul_(rank)
            tensor = tensor.type(dtype)
            gathered = hvd.allgather(tensor)

            assert list(gathered.shape) == [17 * size] + [17] * (dim - 1)

            for i in range(size):
                rank_tensor = gathered[i * 17:(i + 1) * 17]
                assert list(rank_tensor.shape) == [17] * dim, \
                    'hvd.allgather produces incorrect gathered shape'
                assert rank_tensor.data.min() == i, 'hvd.allgather produces incorrect gathered tensor'
                assert rank_tensor.data.max() == i, 'hvd.allgather produces incorrect gathered tensor'

    def test_horovod_allgather_variable_size(self):
        """Test that the allgather correctly gathers 1D, 2D, 3D tensors,
        even if those tensors have different sizes along the first dim."""
        hvd.init()
        rank = hvd.rank()
        size = hvd.size()

        dtypes = [torch.ByteTensor, torch.CharTensor, torch.ShortTensor,
                  torch.IntTensor, torch.LongTensor, torch.FloatTensor, torch.DoubleTensor]
        if torch.cuda.is_available():
            dtypes += [torch.cuda.ByteTensor, torch.cuda.CharTensor, torch.cuda.ShortTensor,
                       torch.cuda.IntTensor, torch.cuda.LongTensor,
                       torch.cuda.FloatTensor, torch.cuda.DoubleTensor]
            if _fp16_supported:
                dtypes += [torch.cuda.HalfTensor]
        dims = [1, 2, 3]
        for dtype, dim in itertools.product(dtypes, dims):
            # Support tests up to MPI Size of 35
            if size > 35:
                break

            tensor_sizes = [17, 32, 81, 12, 15, 23, 22] * 5
            tensor_sizes = tensor_sizes[:size]

            tensor = torch.FloatTensor(
                *([tensor_sizes[rank]] + [17] * (dim - 1))).fill_(1).mul_(rank)
            tensor = tensor.type(dtype)
            gathered = hvd.allgather(tensor)

            expected_size = sum(tensor_sizes)
            assert list(gathered.shape) == [expected_size] + [17] * (dim - 1)

            for i in range(size):
                rank_size = [tensor_sizes[i]] + [17] * (dim - 1)
                rank_tensor = gathered[sum(
                    tensor_sizes[:i]):sum(tensor_sizes[:i + 1])]
                assert list(rank_tensor.shape) == rank_size
                assert rank_tensor.data.min() == i
                assert rank_tensor.data.max() == i

    def test_horovod_allgather_error(self):
        """Test that the allgather returns an error if any dimension besides
        the first is different among the tensors being gathered."""
        hvd.init()
        rank = hvd.rank()
        size = hvd.size()

        # This test does not apply if there is only one worker.
        if size == 1:
            return

        tensor_size = [17] * 3
        tensor_size[1] = 10 * (rank + 1)
        tensor = torch.FloatTensor(*tensor_size).fill_(1).mul_(rank)

        try:
            hvd.allgather(tensor)
            assert False, 'hvd.allgather did not throw error'
        except (torch.FatalError, RuntimeError):
            pass

    def test_horovod_allgather_type_error(self):
        """Test that the allgather returns an error if the types being gathered
        differ among the processes"""
        hvd.init()
        rank = hvd.rank()
        size = hvd.size()

        # This test does not apply if there is only one worker.
        if size == 1:
            return

        tensor_size = [17] * 3
        if rank % 2 == 0:
            tensor = torch.IntTensor(*tensor_size)
        else:
            tensor = torch.FloatTensor(*tensor_size)

        try:
            hvd.allgather(tensor)
            assert False, 'hvd.allgather did not throw error'
        except (torch.FatalError, RuntimeError):
            pass

    def test_horovod_allgather_grad(self):
        """Test the correctness of the allgather gradient."""
        hvd.init()
        rank = hvd.rank()
        size = hvd.size()

        # Only Tensors of floating point dtype can require gradients
        dtypes = [torch.FloatTensor, torch.DoubleTensor]
        if torch.cuda.is_available():
            dtypes += [torch.cuda.FloatTensor, torch.cuda.DoubleTensor]
            if _fp16_supported:
                dtypes += [torch.cuda.HalfTensor]
        dims = [1, 2, 3]
        for dtype, dim in itertools.product(dtypes, dims):
            # Support tests up to MPI Size of 35
            if size > 35:
                break

            tensor_sizes = [3, 2, 7, 4, 6, 8, 10] * 5
            tensor_sizes = tensor_sizes[:size]

            tensor = torch.FloatTensor(
                *([tensor_sizes[rank]] + [17] * (dim - 1))).fill_(1).mul_(rank)
            tensor = tensor.type(dtype)
            tensor.requires_grad_()

            grad_list = []
            for r, size in enumerate(tensor_sizes):
                grad_list.append(torch.ones([size] + [17] * (dim - 1)).type(dtype) * r)
            grad_ys = torch.cat(grad_list, dim=0)

            gathered = hvd.allgather(tensor)
            gathered.backward(grad_ys)
            grad_out = tensor.grad.data.cpu().numpy()

            expected = np.ones(
                [tensor_sizes[rank]] + [17] * (dim - 1)
            ) * rank * size
            err = np.linalg.norm(expected - grad_out)
            self.assertLess(err, 0.00000001,
                            "gradient %s differs from expected %s, "
                            "error: %s" % (grad_out, expected, str(err)))

    def test_horovod_broadcast(self):
        """Test that the broadcast correctly broadcasts 1D, 2D, 3D tensors."""
        hvd.init()
        rank = hvd.rank()
        size = hvd.size()

        # This test does not apply if there is only one worker.
        if size == 1:
            return

        dtypes = [torch.ByteTensor, torch.CharTensor, torch.ShortTensor,
                  torch.IntTensor, torch.LongTensor, torch.FloatTensor, torch.DoubleTensor]
        if torch.cuda.is_available():
            dtypes += [torch.cuda.ByteTensor, torch.cuda.CharTensor, torch.cuda.ShortTensor,
                       torch.cuda.IntTensor, torch.cuda.LongTensor,
                       torch.cuda.FloatTensor, torch.cuda.DoubleTensor]
            if _fp16_supported:
                dtypes += [torch.cuda.HalfTensor]
        dims = [1, 2, 3]
        root_ranks = list(range(size))
        for dtype, dim, root_rank in itertools.product(dtypes, dims, root_ranks):
            tensor = torch.FloatTensor(*([17] * dim)).fill_(1).mul_(rank)
            root_tensor = torch.FloatTensor(*([17] * dim)).fill_(1).mul_(root_rank)
            tensor = tensor.type(dtype)
            root_tensor = root_tensor.type(dtype)
            broadcasted_tensor = hvd.broadcast(tensor, root_rank)
            if rank != root_rank:
                assert (tensor == root_tensor).max() == 0, \
                    'hvd.broadcast modifies source tensor'
            assert (broadcasted_tensor.data == root_tensor).min() == 1, \
                'hvd.broadcast produces incorrect broadcasted tensor'

    def test_horovod_broadcast_inplace(self):
        """Test that the broadcast correctly broadcasts 1D, 2D, 3D tensors."""
        hvd.init()
        rank = hvd.rank()
        size = hvd.size()

        # This test does not apply if there is only one worker.
        if size == 1:
            return

        dtypes = [torch.ByteTensor, torch.CharTensor, torch.ShortTensor,
                  torch.IntTensor, torch.LongTensor, torch.FloatTensor, torch.DoubleTensor]
        if torch.cuda.is_available():
            dtypes += [torch.cuda.ByteTensor, torch.cuda.CharTensor, torch.cuda.ShortTensor,
                       torch.cuda.IntTensor, torch.cuda.LongTensor,
                       torch.cuda.FloatTensor, torch.cuda.DoubleTensor]
            if _fp16_supported:
                dtypes += [torch.cuda.HalfTensor]
        dims = [1, 2, 3]
        root_ranks = list(range(size))
        for dtype, dim, root_rank in itertools.product(dtypes, dims, root_ranks):
            tensor = torch.FloatTensor(*([17] * dim)).fill_(1).mul_(rank)
            root_tensor = torch.FloatTensor(*([17] * dim)).fill_(1).mul_(root_rank)
            tensor = tensor.type(dtype)
            root_tensor = root_tensor.type(dtype)
            broadcasted_tensor = hvd.broadcast_(tensor, root_rank)
            assert (tensor == broadcasted_tensor).min() == 1, \
                'hvd.broadcast does not modify source tensor'
            assert (broadcasted_tensor == root_tensor).min() == 1, \
                'hvd.broadcast produces incorrect broadcasted tensor'

    def test_horovod_broadcast_error(self):
        """Test that the broadcast returns an error if any dimension besides
        the first is different among the tensors being broadcasted."""
        hvd.init()
        rank = hvd.rank()
        size = hvd.size()

        # This test does not apply if there is only one worker.
        if size == 1:
            return

        tensor_size = [17] * 3
        tensor_size[1] = 10 * (rank + 1)
        tensor = torch.FloatTensor(*tensor_size).fill_(1).mul_(rank)

        try:
            hvd.broadcast(tensor, 0)
            assert False, 'hvd.broadcast did not throw error'
        except (torch.FatalError, RuntimeError):
            pass

    def test_horovod_broadcast_type_error(self):
        """Test that the broadcast returns an error if the types being broadcasted
        differ among the processes"""
        hvd.init()
        rank = hvd.rank()
        size = hvd.size()

        # This test does not apply if there is only one worker.
        if size == 1:
            return

        tensor_size = [17] * 3
        if rank % 2 == 0:
            tensor = torch.IntTensor(*tensor_size)
        else:
            tensor = torch.FloatTensor(*tensor_size)

        try:
            hvd.broadcast(tensor, 0)
            assert False, 'hvd.broadcast did not throw error'
        except (torch.FatalError, RuntimeError):
            pass

    def test_horovod_broadcast_rank_error(self):
        """Test that the broadcast returns an error if different ranks
        specify different root rank."""
        hvd.init()
        rank = hvd.rank()
        size = hvd.size()

        # This test does not apply if there is only one worker.
        if size == 1:
            return

        tensor = torch.FloatTensor(*([17] * 3)).fill_(1)

        try:
            hvd.broadcast(tensor, rank)
            assert False, 'hvd.broadcast did not throw error'
        except (torch.FatalError, RuntimeError):
            pass

    def test_horovod_broadcast_grad(self):
        """Test the correctness of the broadcast gradient."""
        hvd.init()
        rank = hvd.rank()
        size = hvd.size()

        # This test does not apply if there is only one worker.
        if size == 1:
            return

        # Only Tensors of floating point dtype can require gradients
        dtypes = [torch.FloatTensor, torch.DoubleTensor]
        if torch.cuda.is_available():
            dtypes += [torch.cuda.FloatTensor, torch.cuda.DoubleTensor]
            if _fp16_supported:
                dtypes += [torch.cuda.HalfTensor]
        dims = [1, 2, 3]
        root_ranks = list(range(size))
        for dtype, dim, root_rank in itertools.product(dtypes, dims, root_ranks):
            tensor = torch.FloatTensor(*([17] * dim)).fill_(1).mul_(rank)
            tensor = tensor.type(dtype)
            tensor.requires_grad_()

            broadcasted_tensor = hvd.broadcast(tensor, root_rank)
            broadcasted_tensor.backward(torch.ones([17] * dim).type(dtype))
            grad_out = tensor.grad.data.cpu().numpy()

            c = size if rank == root_rank else 0
            expected = np.ones([17] * dim) * c
            err = np.linalg.norm(expected - grad_out)
            self.assertLess(err, 0.00000001,
                            "gradient %s differs from expected %s, "
                            "error: %s" % (grad_out, expected, str(err)))

    def test_broadcast_state(self):
        hvd.init()

        N, D_in, H, D_out = 64, 100, 10, 10
        x = torch.randn(N, D_in).requires_grad_()
        y = torch.randn(N, D_out).requires_grad_()

        def create_model(create_opt):
            model = torch.nn.Sequential(
                torch.nn.Linear(D_in, H),
                torch.nn.ReLU(),
                torch.nn.Linear(H, D_out),
            )

            optimizer = create_opt(model)
            optimizer = hvd.DistributedOptimizer(
                optimizer, named_parameters=model.named_parameters())

            return model, optimizer

        def get_model_param_values(model):
            params = sorted(model.state_dict().items())
            return [(k, v.clone()) for k, v in params]

        def get_optimizer_param_values(optimizer):
            results = []
            state_dict = optimizer.state_dict()
            for group in state_dict['param_groups']:
                for param_id in group['params']:
                    params = sorted(state_dict['state'][param_id].items())
                    for k, v in params:
                        results.append(
                            (k, v.clone() if torch.is_tensor(v) else v))
            return results

        opt_params = dict(lr=0.2, momentum=0.9, weight_decay=0.1, centered=True)

        def new_optimizer(cls):
            p = {
                k: v for k, v in opt_params.items()
                if k in inspect.getargspec(cls.__init__).args
            }
            return lambda m: cls(m.parameters(), **p)

        # L-BFGS is currently unsupported, as are sparse tensors, which are
        # required by SparseAdam optimizer
        optimizers = [
            (subclass.__name__, new_optimizer(subclass))
            for subclass in torch.optim.Optimizer.__subclasses__()
            if subclass.__module__.startswith('torch.optim') and
               subclass != torch.optim.LBFGS and
               subclass != torch.optim.SparseAdam
        ]
        optimizers.sort()

        for opt_name, create_opt in optimizers:
            model, optimizer = create_model(create_opt)
            y_pred = model(x)
            loss = F.mse_loss(y_pred, y, size_average=False)
            optimizer.zero_grad()
            loss.backward()
            optimizer.step()

            model_param_values = get_model_param_values(model)
            for name, model_param_value in model_param_values:
                hvd.broadcast_(model_param_value, root_rank=0)

            opt_param_values_updated = []
            opt_param_values = get_optimizer_param_values(optimizer)
            for name, opt_param_value in opt_param_values:
                is_tensor = torch.is_tensor(opt_param_value)
                if not is_tensor:
                    t = type(opt_param_value)
                    opt_param_value = torch.Tensor([opt_param_value])
                hvd.broadcast_(opt_param_value, root_rank=0)
                if not is_tensor:
                    opt_param_value = t(opt_param_value.cpu().numpy()[0])
                opt_param_values_updated.append((name, opt_param_value))
            opt_param_values = opt_param_values_updated

            if hvd.rank() == 0:
                state = {
                    'model': model.state_dict(),
                    'optimizer': optimizer.state_dict(),
                }
                _, fname = tempfile.mkstemp('.pt')
                torch.save(state, fname)

            model, optimizer = create_model(create_opt)
            if hvd.rank() == 0:
                checkpoint = torch.load(fname)
                model.load_state_dict(checkpoint['model'])
                optimizer.load_state_dict(checkpoint['optimizer'])
                os.remove(fname)

            hvd.broadcast_parameters(model.state_dict(), root_rank=0)
            model_param_value_after = get_model_param_values(model)
            for before, after in zip(model_param_values,
                                     model_param_value_after):
                name, model_param_value = before
                name_after, model_param_value_after = after
                self.assertEqual(name, name_after)
                self.assertEqual(type(model_param_value),
                                 type(model_param_value_after))
                self.assertTrue(
                    (model_param_value == model_param_value_after).all())

            hvd.broadcast_optimizer_state(optimizer, root_rank=0)
            self.assertEqual(len(optimizer.state_dict()['state'].values()), 4)

            opt_param_values_after = get_optimizer_param_values(optimizer)
            for before, after in zip(opt_param_values, opt_param_values_after):
                name, opt_param_value = before
                name_after, opt_param_value_after = after
                self.assertEqual(name, name_after)
                self.assertEqual(type(opt_param_value),
                                 type(opt_param_value_after))
                if torch.is_tensor(opt_param_value):
                    self.assertTrue(
                        (opt_param_value == opt_param_value_after).all())
                else:
                    self.assertEqual(opt_param_value, opt_param_value_after)

    def test_compression_fp16(self):
        valid_dtypes = [torch.float32, torch.float64]
        invalid_dtypes = [torch.uint8, torch.int8, torch.int16,
                          torch.int32, torch.int64]

        tensor_size = [5] * 3
        compression = hvd.Compression.fp16

        for dtype in valid_dtypes:
            tensor = torch.ones(tensor_size, dtype=dtype)

            tensor_compressed, ctx = compression.compress(tensor)
            self.assertEqual(tensor_compressed.dtype, torch.float16)

            tensor_decompressed = compression.decompress(tensor_compressed, ctx)
            self.assertEqual(tensor_decompressed.dtype, dtype)

            expected = np.ones(tensor_size)
            err = np.linalg.norm(expected - tensor_decompressed.data.numpy())
            self.assertLess(err, 0.00000001)

        for dtype in invalid_dtypes:
            tensor = torch.ones(tensor_size, dtype=dtype)

            tensor_compressed, ctx = compression.compress(tensor)
            self.assertEqual(tensor_compressed.dtype, dtype)

            tensor_decompressed = compression.decompress(tensor_compressed, ctx)
            self.assertEqual(tensor_decompressed.dtype, dtype)

            if dtype != torch.int8:  # Cannot cast to NumPy with a CharTensor
                expected = np.ones(tensor_size)
                err = np.linalg.norm(expected - tensor_decompressed.data.numpy())
                self.assertLess(err, 0.00000001)