test_optimizer.py

# Copyright (c) 2023, NVIDIA CORPORATION. All rights reserved.
from copy import deepcopy
from functools import partial
from time import sleep
from types import MethodType, SimpleNamespace
from unittest import mock
from unittest.mock import MagicMock

import numpy as np
import pytest
import torch
from torch.optim import Adam

from megatron.core import parallel_state, DistributedDataParallel as DDP
from megatron.core.dist_checkpointing import ShardedTensor, save, load, \
    load_tensors_metadata, load_plain_tensors
from megatron.core.dist_checkpointing.dict_utils import nested_values, diff
from megatron.core.dist_checkpointing.optimizer import \
    get_param_id_to_sharded_param_map, optim_state_to_sharding_state
from megatron.core.dist_checkpointing.serialization import \
    get_default_save_sharded_strategy
from megatron.core.dist_checkpointing.strategies.fully_parallel import \
    FullyParallelSaveStrategyWrapper
from megatron.core.dist_checkpointing.utils import extract_sharded_tensors
from megatron.core.models.gpt import GPTModel
from megatron.core.models.gpt.gpt_layer_specs import get_gpt_layer_local_spec
from megatron.core.optimizer import DistributedOptimizer, OptimizerConfig, \
    get_megatron_optimizer
from megatron.core.tensor_parallel import model_parallel_cuda_manual_seed
from megatron.core.transformer import TransformerConfig
from megatron.core.transformer.mlp import apply_swiglu_sharded_factory
from megatron.core.utils import get_model_config
from megatron.training.checkpointing import load_checkpoint, save_checkpoint
from megatron.training.training import get_model
from megatron.training.utils import unwrap_model
from pretrain_gpt import model_provider

from tests.unit_tests.dist_checkpointing import TempNamedDir
from tests.unit_tests.test_utilities import Utils


class Model(torch.nn.Module):
    def __init__(self):
        super().__init__()
        self.conv = torch.nn.Conv1d(8, 16, 3)
        self.proj = torch.nn.Linear(8, 5)
        self.config = TransformerConfig(hidden_size=8, num_attention_heads=1, num_layers=1)

    def sharded_state_dict(self):
        sharded_state_dict = self.state_dict(keep_vars=True)
        # conv
        sharded_state_dict['conv.weight'] = ShardedTensor.from_rank_offsets(
            'conv.weight', sharded_state_dict['conv.weight'],
            (1, parallel_state.get_tensor_model_parallel_rank(), parallel_state.get_tensor_model_parallel_world_size())
        )
        # bias is non-sharded
        sharded_state_dict['conv.bias'] = ShardedTensor.from_rank_offsets('conv.bias', sharded_state_dict['conv.bias'])

        # proj
        sharded_state_dict['proj.weight'] = ShardedTensor.from_rank_offsets(
            'proj.weight', sharded_state_dict['proj.weight'],
            (0, Utils.rank, Utils.world_size)
        )
        sharded_state_dict['proj.bias'] = ShardedTensor.from_rank_offsets(
            'proj.bias', sharded_state_dict['proj.bias'],
            (0, Utils.rank, Utils.world_size)
        )
        return sharded_state_dict


class SwigluFactoryModel(torch.nn.Module):
    def __init__(self):
        super().__init__()
        self.linear = torch.nn.Linear(5, 64 // parallel_state.get_tensor_model_parallel_world_size(), bias=False)
        self.config = TransformerConfig(hidden_size=8, num_attention_heads=1, num_layers=1)

    def sharded_state_dict(self):
        sharded_state_dict = self.state_dict(keep_vars=True)
        sharded_state_dict['linear.weight'] = ShardedTensor.from_rank_offsets(
            'linear.weight', sharded_state_dict['linear.weight'],
            ((0, parallel_state.get_tensor_model_parallel_rank(), parallel_state.get_tensor_model_parallel_world_size())),
            replica_id=((parallel_state.get_pipeline_model_parallel_rank(), 0, parallel_state.get_data_parallel_rank(with_context_parallel=True)))
        )
        sharded_state_dict['linear.weight'] = apply_swiglu_sharded_factory(sharded_state_dict['linear.weight'], ())
        return sharded_state_dict


class SwigluFactoryModel(torch.nn.Module):
    def __init__(self):
        super().__init__()
        self.linear = torch.nn.Linear(5, 64 // parallel_state.get_tensor_model_parallel_world_size(), bias=False)
        self.config = TransformerConfig(hidden_size=8, num_attention_heads=1, num_layers=1)

    def sharded_state_dict(self):
        sharded_state_dict = self.state_dict(keep_vars=True)
        sharded_state_dict['linear.weight'] = ShardedTensor.from_rank_offsets(
            'linear.weight', sharded_state_dict['linear.weight'],
            ((0, parallel_state.get_tensor_model_parallel_rank(), parallel_state.get_tensor_model_parallel_world_size())),
            replica_id=((parallel_state.get_pipeline_model_parallel_rank(), 0, parallel_state.get_data_parallel_rank(with_context_parallel=True)))
        )
        sharded_state_dict['linear.weight'] = apply_swiglu_sharded_factory(sharded_state_dict['linear.weight'], ())
        return sharded_state_dict


class TestOptimizer:
    def setup_class(cls):
        Utils.initialize_distributed()

    @pytest.fixture(scope='function', autouse=True)
    def cleanup_model_parallel(self):
        # pass for initialize
        yield
        Utils.destroy_model_parallel()

    def test_optimizer_params(self, tmp_path_dist_ckpt):
        Utils.initialize_model_parallel(1,1)
        model = Model()
        # Force optimizer state initialization
        for p in model.parameters():
            p.grad = torch.ones_like(p.data)
        optim = Adam(model.parameters())
        optim.step()

        model_state_dict = model.sharded_state_dict()
        param_map = get_param_id_to_sharded_param_map(model_state_dict, optim.param_groups[0]['params'])
        optim_state_dict = optim.state_dict()
        optim_state_to_sharding_state(optim_state_dict, param_map, exclude_keys=('step',))

        optim_sharded_tensors = nested_values(extract_sharded_tensors(optim_state_dict)[0])
        optim_sharded_keys = {sh_ten.key for sh_ten in optim_sharded_tensors}
        assert len(optim_sharded_keys) == 2 * len(model_state_dict)
        assert optim_sharded_keys == set([
            f'optimizer.state.{state_key}.{layer_name}'
            for state_key in ['exp_avg', 'exp_avg_sq']
            for layer_name in model_state_dict
        ])


def initialize_gpt_model(pre_process=True, post_process=True, seed=0, use_glu=True, **config_kwargs):
    torch.manual_seed(seed)
    model_parallel_cuda_manual_seed(seed)

    default_config_kwargs=dict(num_layers=8, hidden_size=16, num_attention_heads=8, use_cpu_initialization=True)
    default_config_kwargs.update(**config_kwargs)
    transformer_config = TransformerConfig(**default_config_kwargs, gated_linear_unit=use_glu)
    model = GPTModel(config=transformer_config, transformer_layer_spec=get_gpt_layer_local_spec(), vocab_size=128, max_sequence_length=4,
                     pre_process=pre_process, post_process=post_process)

    model.bfloat16()
    with torch.no_grad():
        for p in model.parameters():
            p.random_()
    return model


def initialize_small_model(pre_process=True, post_process=True, seed=0, **config_kwargs):
    torch.manual_seed(seed)
    model_parallel_cuda_manual_seed(seed)

    return SwigluFactoryModel()


def init_basic_mock_args(args, tp, pp, bf16=True):
    args.data_parallel_random_init = False
    args.virtual_pipeline_model_parallel_size = None
    args.fp16 = False
    args.bf16 = bf16
    args.accumulate_allreduce_grads_in_fp32 = False
    args.overlap_grad_reduce = False
    args.use_distributed_optimizer = True
    args.ddp_bucket_size = None
    args.check_for_nan_in_loss_and_grad = False
    args.ddp_average_in_collective = False
    args.tensor_model_parallel_size = tp
    args.pipeline_model_parallel_size = pp
    return args


def init_checkpointing_mock_args(args, ckpt_dir, fully_parallel=False):
    args.save = ckpt_dir
    args.load = ckpt_dir
    args.pretrained_checkpoint = None
    args.ckpt_fully_parallel_save = fully_parallel
    args.ckpt_fully_parallel_load = fully_parallel
    args.async_save = False
    args.use_dist_ckpt = True
    args.dist_ckpt_format = 'torch_dist'
    args.no_save_optim = False
    args.no_save_rng = False
    args.ckpt_assume_constant_structure = False
    args.log_progress = False
    args.auto_detect_ckpt_format = False
    args.exit_on_missing_checkpoint = False
    args.finetune = False
    args.consumed_train_samples = 0
    args.consumed_valid_samples = 0
    args.retro_add_retriever = False
    args.no_load_optim = False
    args.no_load_rng = False
    args.dist_ckpt_strictness = 'assume_ok_unexpected'


def load_checkpoint_no_arg_checks(*args, **kwargs):
    with mock.patch('megatron.training.checkpointing.check_checkpoint_args'):
        with mock.patch('megatron.training.checkpointing.update_num_microbatches'):
            return load_checkpoint(*args, **kwargs)


def setup_model_and_optimizer(seed, tp, pp, initialize_fn=initialize_gpt_model, bf16=True, dist_opt=True):
    mock_args = SimpleNamespace()
    with mock.patch('megatron.training.training.get_args', new=lambda: mock_args):
        init_basic_mock_args(mock_args, tp, pp, bf16=bf16)
        model = get_model(partial(
            initialize_fn, seed=seed, tensor_model_parallel_size=tp, pipeline_model_parallel_size=pp, pipeline_dtype=torch.bfloat16
        ))

    config = OptimizerConfig(bf16=bf16, params_dtype=torch.bfloat16 if bf16 else torch.float, use_distributed_optimizer=dist_opt)
    optimizer = get_megatron_optimizer(config, model)

    torch.manual_seed(seed + 1)
    model_parallel_cuda_manual_seed(seed + 1)

    for group in optimizer.optimizer.param_groups:
        for p in group['params']:
            if len(optimizer.optimizer.state[p]) == 0:
                optimizer.optimizer.state[p]['exp_avg'] = torch.rand_like(p.data)
                optimizer.optimizer.state[p]['exp_avg_sq'] = torch.rand_like(p.data)

    optimizer.reload_model_params()

    return unwrap_model(model), optimizer


class TestDistributedOptimizer:
    def setup_class(cls):
        Utils.initialize_distributed()

    @pytest.fixture(scope='function', autouse=True)
    def cleanup_model_parallel(self):
        # pass for initialize
        yield
        Utils.destroy_model_parallel()

    @pytest.mark.parametrize("initialize_fn", [initialize_small_model, initialize_gpt_model])
    @pytest.mark.parametrize("use_fpsl", [False, True])
    @pytest.mark.parametrize("tp_pp,src_dp,dest_dp", [
        ((4, 1), 2, 2),
        # ((1, 1), 8, 1),  # TODO: changing DP doesn't work in unit tests because of NCCL crashes
        # ((1, 1), 1, 8),
        # ((2, 1), 2, 1),
        # ((2, 1), 2, 2),
    ])
    def test_dp_sharding(self, tmp_path_dist_ckpt, tp_pp, src_dp, dest_dp, use_fpsl, initialize_fn):
        src_world_size = tp_pp[0] * tp_pp[1] * src_dp
        dest_world_size = tp_pp[0] * tp_pp[1] * dest_dp
        assert src_world_size <= Utils.world_size, (tp_pp, src_dp)
        assert dest_world_size <= Utils.world_size, (tp_pp, dest_dp)

        sharding_type = 'fully_sharded_model_space' if use_fpsl else 'dp_zero_gather_scatter'

        # sync=True to make sure other ranks wait for rank 0 to finish creating directory.
        with TempNamedDir(tmp_path_dist_ckpt / 'test_dp_sharding', sync=True) as ckpt_dir:
            try:
                Utils.set_world_size(src_world_size)
                if Utils.rank >= 0:
                    # Save checkpoint A
                    Utils.initialize_model_parallel(*tp_pp)
                    model, optimizer_A = setup_model_and_optimizer(seed=2, tp=tp_pp[0], pp=tp_pp[1], initialize_fn=initialize_fn)

                    save_strategy = get_default_save_sharded_strategy()
                    if use_fpsl:
                        save_strategy = FullyParallelSaveStrategyWrapper(
                            save_strategy,
                            parallel_state.get_data_parallel_group(with_context_parallel=True),
                            True
                        )
                    save(optimizer_A.sharded_state_dict(model[0].sharded_state_dict(), sharding_type=sharding_type), ckpt_dir, save_strategy)
                    optim_param_state_A = optimizer_A.get_parameter_state_dp_zero()
                    Utils.destroy_model_parallel()
                else:
                    # this prevents NCCL errors when changing DP. TODO: fix it properly
                    sleep(20)

                # Load checkpoint A with different TP/PP and save as checkpoint B
                Utils.set_world_size(dest_world_size)
                if Utils.rank == 0:
                    print('_____________________')
                if Utils.rank >= 0:
                    Utils.initialize_model_parallel(*tp_pp)

                    model, optimizer_B = setup_model_and_optimizer(seed=3, tp=tp_pp[0], pp=tp_pp[1], initialize_fn=initialize_fn)
                    optim_param_state_B = optimizer_B.get_parameter_state_dp_zero()
                    diffs = diff(optim_param_state_A, optim_param_state_B)
                    # Expect a mismatch in values - diffs[2] nonempty
                    if parallel_state.get_data_parallel_rank(with_context_parallel=True) == 0:
                        assert not diffs[0] and not diffs[1] and diffs[2], diffs

                    sharded_state_dict = optimizer_B.sharded_state_dict(
                        model[0].sharded_state_dict(),
                        is_loading=True,
                        sharding_type=sharding_type,
                    )
                    optim_state_dict = load(sharded_state_dict, ckpt_dir)
                    optimizer_B.load_state_dict(optim_state_dict)
                    optim_param_state_B = optimizer_B.get_parameter_state_dp_zero()

                    # Test both param state dicts are equal
                    diffs = diff(optim_param_state_A, optim_param_state_B)
                    assert not any(map(bool, diffs)), diffs

                else:
                    # this prevents NCCL errors when changing DP. TODO: fix it properly
                    sleep(20)
            finally:
                Utils.set_world_size()

    @pytest.mark.parametrize(
        ('src_tp_pp', 'dest_tp_pp', 'use_glu'),
        [
            ((2, 2), (2, 4), False,),
            ((1, 8), (4, 1), True),
            ((2, 4), (4, 2), False),
        ]
    )
    def test_finetune_doesnt_load_optimizer(self, tmp_path_dist_ckpt, src_tp_pp, dest_tp_pp, use_glu):
        # sync=True to make sure other ranks wait for rank 0 to finish creating directory.
        with TempNamedDir(tmp_path_dist_ckpt / 'test_finetune_doesnt_load_optimizer', sync=True) as ckpt_dir:
            mock_args = SimpleNamespace()
            with mock.patch('megatron.training.checkpointing.get_args', new=lambda: mock_args):
                init_basic_mock_args(mock_args, tp=src_tp_pp[0], pp=src_tp_pp[1])
                init_checkpointing_mock_args(mock_args, ckpt_dir, False)

                Utils.initialize_model_parallel(*src_tp_pp)
                model, optimizer = setup_model_and_optimizer(
                    seed=2, tp=src_tp_pp[0], pp=src_tp_pp[1], initialize_fn=partial(initialize_gpt_model, use_glu=use_glu)
                )

                save_checkpoint(10, model, optimizer, None, 0)
                Utils.destroy_model_parallel()

                Utils.initialize_model_parallel(*dest_tp_pp)
                model, optimizer = setup_model_and_optimizer(
                    seed=3, tp=dest_tp_pp[0], pp=dest_tp_pp[1], initialize_fn=partial(initialize_gpt_model, use_glu=use_glu)
                )
                model_unloaded_state_dict = deepcopy(model[0].state_dict())
                optim_unloaded_state_dict = deepcopy(optimizer.state_dict())

                # Load with different TPxPP should raise DistributeOptimizer error
                with pytest.raises(RuntimeError) as exc_info:
                    load_checkpoint_no_arg_checks(model, optimizer, None)
                assert "(TP, PP) mismatch" in str(exc_info.value)

                ## Check that the state didn't change
                assert not any(diff(model[0].state_dict(), model_unloaded_state_dict))
                assert not any(diff(optimizer.state_dict(), optim_unloaded_state_dict))

                # Now test the same with a `finetune` flag
                mock_args.finetune = True
                load_checkpoint_no_arg_checks(model, optimizer, None)

                ## Model weights should be different, but optimizer state is unchanged
                diffs = diff(model[0].state_dict(), model_unloaded_state_dict)
                # diffs[0] and diffs[1] is structural diff, diffs[2] is values diff - we expect only values diff
                assert not diffs[0] and not diffs[1] and diffs[2]
                assert not any(diff(optimizer.state_dict(), optim_unloaded_state_dict))

                # ... or `no_load_optim` flag
                model, optimizer = setup_model_and_optimizer(
                    seed=3, tp=dest_tp_pp[0], pp=dest_tp_pp[1], initialize_fn=partial(initialize_gpt_model, use_glu=use_glu)
                )
                mock_args.finetune = False
                mock_args.no_load_optim = True
                mock_args.no_load_rng = True
                load_checkpoint_no_arg_checks(model, optimizer, None)

                ## Model weights should be different, but optimizer state is unchanged
                diffs = (diff(model[0].state_dict(), model_unloaded_state_dict))
                # diffs[0] and diffs[1] is structural diff, diffs[2] is values diff - we expect only values diff
                assert not diffs[0] and not diffs[1] and diffs[2]
                assert not any(diff(optimizer.state_dict(), optim_unloaded_state_dict))


    def test_can_load_deprecated_bucket_space_format(self, tmp_path_dist_ckpt):
        # sync=True to make sure other ranks wait for rank 0 to finish creating directory.
        with TempNamedDir(tmp_path_dist_ckpt / 'test_can_load_deprecated_bucket_space_format', sync=True) as ckpt_dir:
            mock_args = SimpleNamespace()
            with mock.patch('megatron.training.checkpointing.get_args', new=lambda: mock_args):
                tp = 4
                pp = 2

                init_basic_mock_args(mock_args, tp=tp, pp=pp)
                init_checkpointing_mock_args(mock_args, ckpt_dir, True)

                Utils.initialize_model_parallel(tp, pp)
                model, optimizer = setup_model_and_optimizer(seed=2, tp=tp, pp=pp, initialize_fn=initialize_gpt_model)

                # Mock optimizer sharded_state_dict so that it ignores the externally passed sharding_type and uses 'fully_sharded_bucket_space' instead
                orig_optim_sharded_state_dict_fn = optimizer.sharded_state_dict
                def sharded_state_dict_bucket_space(self, *args, sharding_type: str = 'fully_sharded_model_space', **kwargs):
                    return orig_optim_sharded_state_dict_fn(*args, sharding_type='fully_sharded_bucket_space', **kwargs)

                optimizer.sharded_state_dict = MethodType(sharded_state_dict_bucket_space, optimizer)
                save_checkpoint(10, model, optimizer, None, 0)

                flag = 0
                key_list = []
                torch.distributed.barrier()
                if Utils.rank == 0:
                    sharded_metadata = load_tensors_metadata(ckpt_dir / 'iter_0000010')
                    key_list = list(sharded_metadata.keys())
                    # Check if actually using `fully_parallel_bucket_space` format.
                    key = 'optimizer.distributed.dp_group_idx_0.gbuf_idx_0.dtype_(torch.bfloat16, torch.bfloat16).bucket_idx_0.exp_avg_sq'
                    if key in key_list:
                        flag = 1

                tensor = torch.tensor([flag], dtype=torch.long, device='cuda')
                torch.distributed.broadcast(tensor, 0)
                flag = tensor[0].item()
                assert flag == 1, key_list

                optimizer.sharded_state_dict = orig_optim_sharded_state_dict_fn
                load_checkpoint_no_arg_checks(model, optimizer, None)



class TestFP32Optimizer:
    def setup_class(cls):
        Utils.initialize_distributed()

    @pytest.fixture(scope='function', autouse=True)
    def cleanup_model_parallel(self):
        # pass for initialize
        yield
        Utils.destroy_model_parallel()

    @pytest.mark.parametrize(
        ('src_tp_pp', 'dest_tp_pp'),
        [
            ((2, 4), (2, 4)),
            ((2, 4), (4, 2)),
            ((8, 1), (1, 2)),
        ]
    )
    def test_fp32_optimizer_resharding(self, tmp_path_dist_ckpt, src_tp_pp, dest_tp_pp):
        # sync=True to make sure other ranks wait for rank 0 to finish creating directory.
        with TempNamedDir(tmp_path_dist_ckpt / 'test_fp32_optimizer_state_dict_A', sync=True) as ckpt_dir_A:
            with TempNamedDir(tmp_path_dist_ckpt / 'test_fp32_optimizer_state_dict_B', sync=True) as ckpt_dir_B:
                Utils.initialize_model_parallel(*src_tp_pp)
                model_A, optimizer_A = setup_model_and_optimizer(
                    seed=2, tp=src_tp_pp[0], pp=src_tp_pp[1], initialize_fn=initialize_small_model, bf16=False
                )

                save(optimizer_A.sharded_state_dict(model_A[0].sharded_state_dict()), ckpt_dir_A)
                Utils.destroy_model_parallel()

                # Load checkpoint A with different TP/PP and save as checkpoint B
                Utils.initialize_model_parallel(*dest_tp_pp)
                model_B, optimizer_B = setup_model_and_optimizer(
                    seed=3, tp=dest_tp_pp[0], pp=dest_tp_pp[1], initialize_fn=initialize_small_model, bf16=False
                )
                load_sharded_state_dict = optimizer_B.sharded_state_dict(model_B[0].sharded_state_dict())
                state_dict = load(load_sharded_state_dict, ckpt_dir_A)

                optimizer_B.load_state_dict(state_dict)
                save(optimizer_B.sharded_state_dict(model_B[0].sharded_state_dict()), ckpt_dir_B)
                Utils.destroy_model_parallel()

                # Test both checkpoints are equal
                Utils.initialize_model_parallel(1, 1)
                plain_state_dict_A = load_plain_tensors(ckpt_dir_A)
                plain_state_dict_B = load_plain_tensors(ckpt_dir_B)
                diffs = diff(plain_state_dict_A, plain_state_dict_B)
                assert not any(map(bool, diffs)), diffs


class TestOptimizerResharding:
    @pytest.fixture(scope='function', autouse=True)
    def cleanup_model_parallel(self):
        # pass for initialize
        yield
        Utils.destroy_model_parallel()

    @pytest.mark.parametrize(
        ('use_dist_opt', 'bf16'),
        (
            (False, True),  # regular BF16
            (True, True),   # DistOpt BF16
            # (False, False), # FP32
        )
    )
    @pytest.mark.parametrize(
        ('src_tp_pp', 'dest_tp_pp',),
        [
            ((2, 4), (2, 4)),
            ((2, 4), (2, 2)),
            ((2, 4), (4, 2)),
            ((8, 1), (1, 2)),
        ]
    )
    def test_optimizer_resharding(self, tmp_path_dist_ckpt, src_tp_pp, dest_tp_pp, use_dist_opt, bf16):
        with TempNamedDir(tmp_path_dist_ckpt / 'test_fp32_optimizer_state_dict_A', sync=False) as ckpt_dir_A:
            with TempNamedDir(tmp_path_dist_ckpt / 'test_fp32_optimizer_state_dict_B', sync=False) as ckpt_dir_B:
                Utils.initialize_model_parallel(*src_tp_pp)
                model_A, optimizer_A = setup_model_and_optimizer(seed=2, tp=src_tp_pp[0], pp=src_tp_pp[1], bf16=bf16, dist_opt=use_dist_opt)

                save(optimizer_A.sharded_state_dict(model_A[0].sharded_state_dict()), ckpt_dir_A)
                Utils.destroy_model_parallel()

                # Load checkpoint A with different TP/PP and save as checkpoint B
                Utils.initialize_model_parallel(*dest_tp_pp)
                model_B, optimizer_B = setup_model_and_optimizer(seed=3, tp=dest_tp_pp[0], pp=dest_tp_pp[1], bf16=bf16, dist_opt=use_dist_opt)
                load_sharded_state_dict = optimizer_B.sharded_state_dict(model_B[0].sharded_state_dict())
                state_dict = load(load_sharded_state_dict, ckpt_dir_A)

                optimizer_B.load_state_dict(state_dict)
                save(optimizer_B.sharded_state_dict(model_B[0].sharded_state_dict()), ckpt_dir_B)
                Utils.destroy_model_parallel()

                # Test both checkpoints are equal
                Utils.initialize_model_parallel(1, 1)
                plain_state_dict_A = load_plain_tensors(ckpt_dir_A)
                plain_state_dict_B = load_plain_tensors(ckpt_dir_B)
                diffs = diff(plain_state_dict_A, plain_state_dict_B)
                assert not any(map(bool, diffs)), diffs