Added pure_bf16 mode (#32281)

paddle/fluid/operators/assign_op.cc

@@ -162,6 +162,7 @@ REGISTER_OP_CPU_KERNEL_FUNCTOR(assign, float, ops::AssignKernel, double,
                                ops::AssignKernel, int, ops::AssignKernel,
                                int64_t, ops::AssignKernel, bool,
                                ops::AssignKernel, plat::float16,
+                               ops::AssignKernel, plat::bfloat16,
                                ops::AssignKernel);
 
 #if defined(PADDLE_WITH_CUDA) || defined(PADDLE_WITH_HIP)

python/paddle/fluid/contrib/mixed_precision/__init__.py

@@ -20,10 +20,7 @@ from . import fp16_lists
 from .fp16_lists import *
 from . import fp16_utils
 from .fp16_utils import *
-from . import bf16
-from .bf16 import *
 
 __all__ = decorator.__all__
 __all__ += fp16_lists.__all__
 __all__ += fp16_utils.__all__
-__all__ += bf16.__all__

python/paddle/fluid/contrib/mixed_precision/bf16/__init__.py

@@ -18,7 +18,9 @@ from . import amp_lists
 from .amp_lists import *
 from . import amp_utils
 from .amp_utils import *
+from . import decorator
+from .decorator import *
 
-__all__ = []
+__all__ = decorator.__all__
 __all__ += amp_lists.__all__
 __all__ += amp_utils.__all__

python/paddle/fluid/contrib/mixed_precision/bf16/amp_lists.py

@@ -13,8 +13,10 @@
 # limitations under the License.
 
 import copy
+from paddle.fluid import core
+
 from ..fp16_lists import white_list as white_list_fp16, black_list as black_list_fp16,\
-    gray_list as gray_list_fp16, unsupported_fp16_list
+    gray_list as gray_list_fp16
 
 __all__ = ["AutoMixedPrecisionListsBF16"]
 
@@ -82,11 +84,17 @@ bf16_list = {'elementwise_add', }
 
 # depends on the prev_op type
 gray_list = {
+    'cast',
+    'fill_constant',
+    'reduce_mean',
     'reshape2',
-    'lookup_table',
+    'scale',
 }
 
-unsupported_list = unsupported_fp16_list.copy().copy()
+_, _, _sys_unsupported_bf16_list = core.op_supported_infos(
+    'CPU', core.VarDesc.VarType.BF16)
+unsupported_list = _sys_unsupported_bf16_list
+
 fp32_list = black_list_fp16.copy().copy()
 fp32_list |= white_list_fp16
 fp32_list |= gray_list_fp16

python/paddle/fluid/contrib/mixed_precision/bf16/amp_utils.py

@@ -14,18 +14,25 @@
 # limitations under the License.
 
 from __future__ import print_function
-import struct
 
 from .... import core
 from .... import framework
+from .... import global_scope
 from ....log_helper import get_logger
 from ....wrapped_decorator import signature_safe_contextmanager
 from .amp_lists import AutoMixedPrecisionListsBF16
-from ..fp16_utils import find_true_prev_op, find_true_post_op, _rename_arg, find_op_index
+from ..fp16_utils import find_true_prev_op, find_true_post_op, _rename_arg, \
+    find_op_index, _rename_op_input
+
+import collections
+import struct
 import logging
 import numpy as np
 
-__all__ = ["bf16_guard", "rewrite_program_bf16", "convert_float_to_uint16"]
+__all__ = [
+    "bf16_guard", "rewrite_program_bf16", "cast_model_to_bf16",
+    "cast_parameters_to_bf16", "convert_float_to_uint16"
+]
 
 _logger = get_logger(
     __name__, logging.INFO, fmt='%(asctime)s-%(levelname)s: %(message)s')
@@ -126,7 +133,41 @@ def _insert_cast_op(block, op, idx, src_dtype, dest_dtype):
     return num_cast_ops
 
 
+def _insert_cast_post_op(block, op, idx, src_dtype, dest_dtype, target_name,
+                         op_var_rename_map):
+    num_cast_ops = 0
+    target_var = block.var(target_name)
+    if target_var.type not in _valid_types or target_var.dtype == dest_dtype:
+        return num_cast_ops
+
+    assert target_var.dtype == src_dtype, \
+        "The real dtype({}) is not equal to the src dtype({})".format(_dtype_to_str(target_var.dtype), _dtype_to_str(src_dtype))
+
+    cast_name = target_var.name + '.cast_' + _dtype_to_str(dest_dtype)
+    cast_var = block.vars.get(cast_name)
+    if cast_var is None or cast_var.dtype != dest_dtype:
+        cast_var = block.create_var(
+            name=cast_name,
+            dtype=dest_dtype,
+            persistable=False,
+            stop_gradient=target_var.stop_gradient)
+        block._insert_op(
+            idx,
+            type="cast",
+            inputs={"X": target_var},
+            outputs={"Out": cast_var},
+            attrs={"in_dtype": target_var.dtype,
+                   "out_dtype": cast_var.dtype})
+        num_cast_ops += 1
+        op_var_rename_map[block.idx][target_var.name] = cast_var.name
+
+    return num_cast_ops
+
+
 def _is_in_fp32_varnames(op, amp_lists):
+    if not amp_lists.fp32_varnames:
+        return False
+
     for in_name in op.input_arg_names:
         if in_name in amp_lists.fp32_varnames:
             return True
@@ -191,7 +232,174 @@ def bf16_guard():
         yield
 
 
-def rewrite_program_bf16(main_prog, amp_lists=None, use_bf16_guard=False):
+def cast_model_to_bf16(program, amp_lists=None, use_bf16_guard=True):
+    """
+    Traverse all ops in the whole model and set their inputs and outputs
+    to the bf16 data type. This function will do some special processing for
+    the batch normalization, which will keep the batchnorm's computations in FP32.
+    Args:
+        program (Program): The used program.
+        amp_lists (AutoMixedPrecisionListsBF16): An AutoMixedPrecisionListsBF16 object.
+        use_bf16_guard(bool): Determine whether to use `bf16_guard` when
+                              constructing the program. Default True.
+    """
+
+    if amp_lists is None:
+        amp_lists = AutoMixedPrecisionListsBF16()
+    global_block = program.global_block()
+    keep_fp32_ops = set()
+    to_bf16_var_names = set()
+    to_bf16_pre_cast_ops = set()
+    origin_ops = []
+    for block in program.blocks:
+        origin_ops.extend(block.ops)
+
+    for block in program.blocks:
+        ops = block.ops
+        for op in ops:
+            if op.type == 'create_py_reader' or op.type == 'read':
+                continue
+            if _need_keep_fp32(op, amp_lists.unsupported_list, use_bf16_guard):
+                keep_fp32_ops.add(op)
+                continue  # processed below
+            for in_name in op.input_names:
+                if op.type in {
+                        'batch_norm', 'fused_bn_add_activation', 'layer_norm'
+                } and in_name not in {'X', 'Z'}:
+                    continue
+                for in_var_name in op.input(in_name):
+                    in_var = None
+                    try:
+                        in_var = block.var(in_var_name)
+                    except ValueError as e:
+                        _logger.debug(
+                            "-- {}, try to get it in the global block --".
+                            format(e))
+                        in_var = global_block.var(in_var_name)
+                        if in_var is not None:
+                            _logger.debug(
+                                "-- var {} is got in the global block --".
+                                format(in_var_name))
+
+                    if in_var is None or in_var.type not in _valid_types:
+                        continue
+
+                    if in_var.dtype == core.VarDesc.VarType.FP32:
+                        in_var.desc.set_dtype(core.VarDesc.VarType.BF16)
+                        to_bf16_var_names.add(in_var_name)
+
+                    _logger.debug(
+                        "-- op type: {}, in var name: {}, in var dtype: {} --".
+                        format(op.type, in_var_name, in_var.dtype))
+
+            for out_name in op.output_names:
+                if op.type in {
+                        'batch_norm', 'fused_bn_add_activation', 'layer_norm'
+                } and out_name != 'Y':
+                    continue
+                for out_var_name in op.output(out_name):
+                    out_var = None
+                    try:
+                        out_var = block.var(out_var_name)
+                    except ValueError as e:
+                        _logger.debug(
+                            "-- {}, try to get it in the global block --".
+                            format(e))
+                        out_var = global_block.var(out_var_name)
+                        if out_var is not None:
+                            _logger.debug(
+                                "-- var {} is got in the global block --".
+                                format(out_var_name))
+
+                    if out_var is None or out_var.type not in _valid_types:
+                        continue
+
+                    if out_var.dtype == core.VarDesc.VarType.FP32:
+                        out_var.desc.set_dtype(core.VarDesc.VarType.BF16)
+
+                    _logger.debug(
+                        "-- op type: {}, out var name: {}, out var dtype: {} --".
+                        format(op.type, out_var_name, out_var.dtype))
+            for attr_name in ['in_dtype', 'out_dtype', 'dtype']:
+                if op.has_attr(attr_name) and op.attr(
+                        attr_name) == core.VarDesc.VarType.FP32:
+                    op._set_attr(attr_name, core.VarDesc.VarType.BF16)
+            if op.has_attr('use_mkldnn'):
+                op._set_attr('use_mkldnn', True)
+            if op.has_attr('mkldnn_data_type'):
+                op._set_attr('mkldnn_data_type', 'bfloat16')
+
+    # process ops in keep_fp32_ops
+    op_var_rename_map = [
+        collections.OrderedDict() for _ in range(len(program.blocks))
+    ]
+    for block in program.blocks:
+        ops = block.ops
+        idx = 0
+        while idx < len(ops):
+            op = ops[idx]
+            num_cast_ops = 0
+            if op not in keep_fp32_ops:
+                if op in to_bf16_pre_cast_ops:
+                    in_var_cast_num = _insert_cast_op(block, op, idx,
+                                                      core.VarDesc.VarType.FP32,
+                                                      core.VarDesc.VarType.BF16)
+                    num_cast_ops += in_var_cast_num
+            else:
+                pre_cast_num = _insert_cast_op(block, op, idx,
+                                               core.VarDesc.VarType.BF16,
+                                               core.VarDesc.VarType.FP32)
+                num_cast_ops += pre_cast_num
+                for out_var_name in op.output_arg_names:
+                    out_var = block.vars.get(out_var_name)
+                    if out_var is None or out_var.type not in _valid_types:
+                        continue
+                    if out_var.dtype == core.VarDesc.VarType.BF16:
+                        out_var.desc.set_dtype(core.VarDesc.VarType.FP32)
+                        post_ops = find_true_post_op(ops, op, out_var_name)
+                        for post_op in post_ops:
+                            if post_op in keep_fp32_ops:
+                                continue
+                            post_cast_num = _insert_cast_post_op(
+                                block, op, idx + pre_cast_num + 1,
+                                core.VarDesc.VarType.FP32,
+                                core.VarDesc.VarType.BF16, out_var_name,
+                                op_var_rename_map)
+                            num_cast_ops += post_cast_num
+            idx += num_cast_ops + 1
+
+    _rename_op_input(program, op_var_rename_map, origin_ops, keep_fp32_ops)
+    return to_bf16_var_names
+
+
+def cast_parameters_to_bf16(place, program, scope=None, to_bf16_var_names=None):
+    """
+    Traverse all parameters in the whole model and set them to the BF16 data type.
+    Whereas, this function will keep parameters of batchnorms in FP32.
+    Args:
+        place(fluid.CPUPlace|fluid.CUDAPlace): `place` is used to restore the BF16 weight tensors.
+        program (Program): The used program.
+        scope(fluid.Scope, optional): `scope` is used to get the FP32 weight tensor values.
+                                      Default is None.
+        to_bf16_var_names(set|list, optional): The data types of vars in `to_bf16_var_names`
+                                               will be set to BF16. Usually, it is the returned
+                                               value of `cast_model_to_bf16` API.
+    """
+    all_parameters = []
+    for block in program.blocks:
+        all_parameters.extend(block.all_parameters())
+
+    bf16_var_names = to_bf16_var_names if to_bf16_var_names else set()
+    var_scope = scope if scope else global_scope()
+    for param in all_parameters:
+        if param.name in bf16_var_names:
+            _logger.debug("---- cast {} to bf16 dtype ----".format(param.name))
+            param_t = var_scope.find_var(param.name).get_tensor()
+            data = np.array(param_t)
+            param_t.set(convert_float_to_uint16(data), place)
+
+
+def rewrite_program_bf16(main_prog, amp_lists=None):
     """
     Traverse all ops in current block and insert cast op according to
     which set current op belongs to.
@@ -231,8 +439,7 @@ def rewrite_program_bf16(main_prog, amp_lists=None, use_bf16_guard=False):
             fp32_op_set.add(op)
             continue
 
-        if op.type in amp_lists.fp32_list or _need_keep_fp32(
-                op, amp_lists.unsupported_list, use_bf16_guard):
+        if op.type in amp_lists.fp32_list:
             fp32_op_set.add(op)
         elif op.type in amp_lists.bf16_list:
             bf16_op_set.add(op)

python/paddle/fluid/contrib/mixed_precision/bf16/decorator.py

+# Copyright (c) 2021 PaddlePaddle Authors. 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 paddle.fluid import (core, default_main_program, layers, program_guard,
+                          unique_name)
+from .amp_utils import (rewrite_program_bf16, cast_model_to_bf16,
+                        cast_parameters_to_bf16)
+from .amp_lists import AutoMixedPrecisionListsBF16
+import types
+import warnings
+
+__all__ = ["decorate_bf16"]
+
+
+class OptimizerWithMixedPrecision(object):
+    """
+    Optimizer with mixed-precision (MP) training. This is a wrapper of a common 
+    optimizer, plus the support of mixed-precision pre-training. The object
+    of this class almost has the same behavior as the common optimizer, with the 
+    methods `minimize()`, `backward()`, `apply_gradients()` implemented. 
+    Additionally, it enables the MP training automatically, i.e, the creation 
+    and maintenance of master parameters, scaling of loss, etc.
+
+    Args:
+        optimizer (Optimizer): A common Optimizer object.
+        amp_lists (CustomOpLists): An CustomOpLists object.
+        use_pure_bf16(bool): Whether to use the pure bf16 training.
+        use_bf16_guard(bool): Whether to use `bf16_guard` when constructing the program.
+
+    """
+
+    def __init__(self, optimizer, amp_lists, use_pure_bf16, use_bf16_guard):
+        self._optimizer = optimizer
+        self._amp_lists = amp_lists
+        self._param_grads = None
+        self._train_program = None
+
+        self._learning_rate = optimizer._learning_rate
+        self._learning_rate_map = optimizer._learning_rate_map
+        self._use_pure_bf16 = use_pure_bf16
+        self._use_bf16_guard = use_bf16_guard
+        self._to_bf16_var_names = None
+
+    def _init_amp_var(self):
+        # Ensure the data type of learning rate vars is float32 (same as the
+        # master parameter dtype)
+        if isinstance(self._optimizer._learning_rate, float):
+            self._optimizer._learning_rate_map[default_main_program()] = \
+                    layers.create_global_var(
+                    name=unique_name.generate("learning_rate"),
+                    shape=[1],
+                    value=float(self._optimizer._learning_rate),
+                    dtype='float32',
+                    persistable=True)
+
+    def backward(self,
+                 loss,
+                 startup_program=None,
+                 parameter_list=None,
+                 no_grad_set=None,
+                 callbacks=None):
+        """
+        Backward propagation or auto differentiation for gradients' computation.
+
+        Args:
+            loss (Variable): The loss Variable to minimize.
+            startup_program (Program|None): The startup Program for initializing 
+                                       parameters in `parameter_list`.
+            parameter_list (list|None): A list of Variables to update.
+            no_grad_set (set|None): A set of Variables should be ignored.
+            callbacks (list|None): A list of callable objects to run when appending
+                                   backward operator for one parameter.
+
+        Returns:
+            A list of (param, grad), which is a tuple of a parameter and its 
+            gradient respectively, and the scaled loss.
+        """
+        train_program = loss.block.program
+        self._train_program = train_program
+
+        with program_guard(self._train_program, startup_program):
+            self._init_amp_var()
+
+            if self._use_pure_bf16:
+                self._to_bf16_var_names = cast_model_to_bf16(
+                    self._train_program, self._amp_lists, self._use_bf16_guard)
+            else:
+                rewrite_program_bf16(self._train_program, self._amp_lists)
+
+            if loss.dtype != core.VarDesc.VarType.FP32:
+                loss = loss.astype('float32')
+
+            params_grads = self._optimizer.backward(
+                loss, startup_program, parameter_list, no_grad_set, callbacks)
+        return params_grads
+
+    def amp_init(self,
+                 place,
+                 scope=None,
+                 test_program=None,
+                 use_bf16_test=False):
+        """
+        Init the amp training, such as cast fp32 parameters to bf16 type.
+  
+        Args:
+            place(CPUPlace): place is used to initialize 
+                bf16 parameters with fp32 values.
+            scope(Scope): The scope is used to find fp32 parameters.
+            test_program(Program): The program is used for testing.
+            use_bf16_test(bool): Whether to use bf16 testing.
+
+        Examples:
+            .. code-block:: python
+
+                import numpy as np
+                import paddle
+                import paddle.nn.functional as F
+                paddle.enable_static()
+
+                def run_example_code():
+                    place = paddle.CPUPlace(0)
+                    exe = paddle.static.Executor(place)
+                    data = paddle.static.data(name='X', shape=[None, 1, 28, 28], dtype='float32')
+                    conv2d = paddle.static.nn.conv2d(input=data, num_filters=6, filter_size=3)
+                    # 1) Use bf16_guard to control the range of bf16 kernels used.
+                    with paddle.static.amp.bf16_guard():
+                        bn = paddle.static.nn.batch_norm(input=conv2d, act="relu")
+                        pool = F.max_pool2d(bn, kernel_size=2, stride=2)
+                        hidden = paddle.static.nn.fc(pool, size=10)
+                        loss = paddle.mean(hidden)
+                    # 2) Create the optimizer and set `multi_precision` to True.
+                    # Setting `multi_precision` to True can avoid the poor accuracy
+                    # or the slow convergence in a way. 
+                    optimizer = paddle.optimizer.Momentum(learning_rate=0.01, multi_precision=True)
+                    # 3) These ops in `custom_fp32_list` will keep in the float32 computation type.
+                    amp_list = paddle.static.amp.CustomOpLists(
+                        custom_fp32_list=['pool2d'])
+                    # 4) The entry of Paddle AMP.
+                    # Enable pure bf16 training by setting `use_pure_bf16` to True.
+                    optimizer = paddle.static.amp.bf16.decorate_bf16(
+                        optimizer,
+                        amp_list,
+                        use_pure_bf16=True)
+                    # If you don't use the default_startup_program(), you sholud pass
+                    # your defined `startup_program` into `minimize`.
+                    optimizer.minimize(loss)
+                    exe.run(paddle.static.default_startup_program())
+                    # 5) Use `amp_init` after FP32 parameters initialization(such as `exe.run(startup_program)`).
+                    # If you want to perform the testing process, you should pass `test_program` into `amp_init`.
+                    optimizer.amp_init(place, scope=paddle.static.global_scope())
+                    
+        """
+        assert self._train_program is not None, \
+            "Please call the minimize method first."
+        if self._use_pure_bf16:
+            cast_parameters_to_bf16(place, self._train_program, scope,
+                                    self._to_bf16_var_names)
+        if test_program is not None:
+            if self._use_pure_bf16:
+                cast_model_to_bf16(test_program, self._amp_lists,
+                                   self._use_bf16_guard)
+            elif use_bf16_test:
+                rewrite_program_bf16(test_program, self._amp_lists)
+
+    def apply_gradients(self, params_grads):
+        """
+        Apply gradients.
+  
+        Args:
+            params_grads (list): A list of params.
+    
+        Returns:
+            A list of optimize operators.
+        """
+
+        return self._optimizer.apply_gradients(params_grads)
+
+    def apply_optimize(self, loss, startup_program, params_grads):
+        program = loss.block.program
+        with program_guard(program, startup_program):
+            optimize_ops = self.apply_gradients(params_grads)
+        return optimize_ops
+
+    def minimize(self,
+                 loss,
+                 startup_program=None,
+                 parameter_list=None,
+                 no_grad_set=None):
+        """
+        Perform optimization by minimizing the given loss.
+
+        Args:
+            loss (Variable): The loss Variable.
+            startup_program (Program): startup_program for initializing parameters
+                in `parameter_list`.
+            parameter_list (list): list of Variables to update.
+            no_grad_set (set|None): set of Variables should be ignored.
+
+        Returns:
+            The scaled loss by scaling factor, the list of optimize ops, and a
+            list of scaled parameters and gradients.
+        """
+        opt_dict = self._optimizer.__class__.__dict__
+        if 'minimize' in opt_dict and isinstance(opt_dict['minimize'],
+                                                 types.FunctionType):
+            warnings.warn(
+                "The decorated optimizer has its own `minimize` method, but it will not be executed."
+            )
+
+        params_grads = self.backward(
+            loss,
+            startup_program=startup_program,
+            parameter_list=parameter_list,
+            no_grad_set=no_grad_set)
+
+        optimize_ops = self.apply_optimize(loss, startup_program, params_grads)
+
+        return optimize_ops, params_grads
+
+
+def decorate_bf16(optimizer,
+                  amp_lists=None,
+                  use_pure_bf16=False,
+                  use_bf16_guard=None):
+    """ 
+    Decorate the given optimizer to adapt to the mixed-precision training.
+
+    Args:
+        optimizer(Optimizer): A common Optimizer.
+        amp_lists (CustomOpLists): An CustomOpLists object.
+        use_pure_bf16(bool): Whether to use the pure bf16 training. Default False.
+        use_bf16_guard(bool): Whether to use `bf16_guard` when constructing the program.
+                           Default None, which means that its value equals to `use_pure_bf16`.
+
+    Returns:
+        An optimizer acting like a normal one but with mixed-precision training 
+        enabled.
+
+    Examples 1:
+	    .. code-block:: python
+
+            # fp32&bf16 list based strategy example
+            import paddle
+            import paddle.static as static
+
+            paddle.enable_static()
+
+            data = static.data(name='X', shape=[None, 1], dtype='float32')
+            hidden = static.nn.fc(x=data, size=10)
+            loss = paddle.mean(hidden)
+            optimizer = paddle.optimizer.Adam(learning_rate=0.001)
+
+            mp_optimizer = static.amp.decorate_bf16(optimizer=optimizer)
+
+            ops, param_grads = mp_optimizer.minimize(loss)
+
+    Examples 2:
+        .. code-block:: python
+
+            # pure bf16 training example
+            import numpy as np
+            import paddle
+            import paddle.nn.functional as F
+
+            def run_example_code():
+                place = paddle.CPUPlace(0)
+                exe = paddle.static.Executor(place)
+                data = paddle.static.data(name='X', shape=[None, 1, 28, 28], dtype='float32')
+                conv2d = paddle.static.nn.conv2d(input=data, num_filters=6, filter_size=3)
+                # 1) Use bf16_guard to control the range of bf16 kernels used.
+                with paddle.static.amp.bf16_guard():
+                    bn = paddle.static.nn.batch_norm(input=conv2d, act="relu")
+                    pool = F.max_pool2d(bn, kernel_size=2, stride=2)
+                    hidden = paddle.static.nn.fc(pool, size=10)
+                    loss = paddle.mean(hidden)
+                # 2) Create the optimizer and set `multi_precision` to True.
+                # Setting `multi_precision` to True can avoid the poor accuracy
+                # or the slow convergence in a way. 
+                optimizer = paddle.optimizer.Momentum(learning_rate=0.01, multi_precision=True)
+                # 3) These ops in `custom_fp32_list` will keep in the float32 computation type.
+                amp_list = paddle.static.amp.CustomOpLists(
+                    custom_fp32_list=['pool2d'])
+                # 4) The entry of Paddle AMP.
+                # Enable pure bf16 training by setting `use_pure_bf16` to True.
+                optimizer = paddle.static.amp.decorate_bf16(
+                    optimizer,
+                    amp_list,
+                    use_pure_bf16=True)
+                # If you don't use the default_startup_program(), you sholud pass
+                # your defined `startup_program` into `minimize`.
+                optimizer.minimize(loss)
+                exe.run(paddle.static.default_startup_program())
+                # 5) Use `amp_init` after FP32 parameters initialization(such as `exe.run(startup_program)`).
+                # If you want to perform the testing process, you should pass `test_program` into `amp_init`.
+                optimizer.amp_init(place, scope=paddle.static.global_scope())
+                
+    """
+    if amp_lists is None:
+        amp_lists = AutoMixedPrecisionListsBF16()
+
+    if use_bf16_guard is None:
+        use_bf16_guard = use_pure_bf16
+
+    mp_optimizer = OptimizerWithMixedPrecision(optimizer, amp_lists,
+                                               use_pure_bf16, use_bf16_guard)
+
+    return mp_optimizer

python/paddle/fluid/contrib/tests/test_bf16_utils.py

@@ -14,7 +14,7 @@
 import copy
 import unittest
 import paddle.fluid as fluid
-import paddle.fluid.contrib.mixed_precision as amp
+import paddle.static.amp as amp
 from paddle.fluid import core
 import paddle
 
@@ -34,34 +34,34 @@ class AMPTest(unittest.TestCase):
         self.assertEqual(self.amp_lists_.gray_list, self.gray_list)
 
     def test_amp_lists(self):
-        self.amp_lists_ = amp.AutoMixedPrecisionListsBF16()
+        self.amp_lists_ = amp.bf16.AutoMixedPrecisionListsBF16()
 
     def test_amp_lists_1(self):
         # 1. w={'exp}, b=None
         self.bf16_list.add('exp')
         self.fp32_list.remove('exp')
 
-        self.amp_lists_ = amp.AutoMixedPrecisionListsBF16({'exp'})
+        self.amp_lists_ = amp.bf16.AutoMixedPrecisionListsBF16({'exp'})
 
     def test_amp_lists_2(self):
         # 2. w={'tanh'}, b=None
         self.fp32_list.remove('tanh')
         self.bf16_list.add('tanh')
 
-        self.amp_lists_ = amp.AutoMixedPrecisionListsBF16({'tanh'})
+        self.amp_lists_ = amp.bf16.AutoMixedPrecisionListsBF16({'tanh'})
 
     def test_amp_lists_3(self):
         # 3. w={'lstm'}, b=None
         self.bf16_list.add('lstm')
 
-        self.amp_lists_ = amp.AutoMixedPrecisionListsBF16({'lstm'})
+        self.amp_lists_ = amp.bf16.AutoMixedPrecisionListsBF16({'lstm'})
 
     def test_amp_lists_4(self):
         # 4. w=None, b={'elementwise_add'}
         self.bf16_list.remove('elementwise_add')
         self.fp32_list.add('elementwise_add')
 
-        self.amp_lists_ = amp.AutoMixedPrecisionListsBF16(
+        self.amp_lists_ = amp.bf16.AutoMixedPrecisionListsBF16(
             custom_fp32_list={'elementwise_add'})
 
     def test_amp_lists_5(self):
@@ -69,28 +69,28 @@ class AMPTest(unittest.TestCase):
         self.fp32_list.add('elementwise_add')
         self.bf16_list.remove('elementwise_add')
 
-        self.amp_lists_ = amp.AutoMixedPrecisionListsBF16(
+        self.amp_lists_ = amp.bf16.AutoMixedPrecisionListsBF16(
             custom_fp32_list={'elementwise_add'})
 
     def test_amp_lists_6(self):
         # 6. w=None, b={'lstm'}
         self.fp32_list.add('lstm')
 
-        self.amp_lists_ = amp.AutoMixedPrecisionListsBF16(
+        self.amp_lists_ = amp.bf16.AutoMixedPrecisionListsBF16(
             custom_fp32_list={'lstm'})
 
     def test_amp_lists_7(self):
         self.fp32_list.add('reshape2')
         self.gray_list.remove('reshape2')
 
-        self.amp_lists_ = amp.AutoMixedPrecisionListsBF16(
+        self.amp_lists_ = amp.bf16.AutoMixedPrecisionListsBF16(
             custom_fp32_list={'reshape2'})
 
     def test_amp_list_8(self):
         self.bf16_list.add('reshape2')
         self.gray_list.remove('reshape2')
 
-        self.amp_lists_ = amp.AutoMixedPrecisionListsBF16(
+        self.amp_lists_ = amp.bf16.AutoMixedPrecisionListsBF16(
             custom_bf16_list={'reshape2'})
 
 
@@ -98,7 +98,7 @@ class AMPTest2(unittest.TestCase):
     def test_amp_lists_(self):
         # 7. w={'lstm'} b={'lstm'}
         # raise ValueError
-        self.assertRaises(ValueError, amp.AutoMixedPrecisionListsBF16,
+        self.assertRaises(ValueError, amp.bf16.AutoMixedPrecisionListsBF16,
                           {'lstm'}, {'lstm'})
 
     def test_find_op_index(self):
@@ -117,10 +117,10 @@ class AMPTest2(unittest.TestCase):
             type="abs", inputs={"X": [var1]}, outputs={"Out": [var2]})
         op2 = block.append_op(
             type="abs", inputs={"X": [var2]}, outputs={"Out": [var3]})
-        amp_lists_1 = amp.AutoMixedPrecisionListsBF16(
+        amp_lists_1 = amp.bf16.AutoMixedPrecisionListsBF16(
             custom_fp32_varnames={'X'})
         assert amp.bf16.amp_utils._is_in_fp32_varnames(op1, amp_lists_1)
-        amp_lists_2 = amp.AutoMixedPrecisionListsBF16(
+        amp_lists_2 = amp.bf16.AutoMixedPrecisionListsBF16(
             custom_fp32_varnames={'Y'})
         assert amp.bf16.amp_utils._is_in_fp32_varnames(op2, amp_lists_2)
         assert amp.bf16.amp_utils._is_in_fp32_varnames(op1, amp_lists_2)

python/paddle/fluid/contrib/tests/test_model_cast_to_bf16.py

@@ -65,13 +65,13 @@ class TestModelCastBF16(unittest.TestCase):
                        fetch_list=fetch_list,
                        return_numpy=(not with_lod))
 
-    def test_graph_rewrite(self):
+    def _graph_common(self, _amp_fun):
         size = 3
         n = np.ones([size, size], dtype='float32') * 3.2
         nn = np.ones([size, size], dtype='float32') * -2.7
 
-        n_bf16 = amp.convert_float_to_uint16(n)
-        nn_bf16 = amp.convert_float_to_uint16(nn)
+        n_bf16 = amp.bf16.convert_float_to_uint16(n)
+        nn_bf16 = amp.bf16.convert_float_to_uint16(nn)
 
         with self.static_graph():
             t_bf16 = layers.data(
@@ -85,12 +85,12 @@ class TestModelCastBF16(unittest.TestCase):
             ret = layers.elementwise_mul(ret, t)
             ret = layers.reshape(ret, [0, 0])
 
-            with amp.bf16_guard():
+            with amp.bf16.bf16_guard():
                 ret_bf16 = layers.elementwise_add(t_bf16, tt_bf16)
                 ret_bf16 = layers.elementwise_mul(ret_bf16, t_bf16)
                 ret_bf16 = layers.reshape(ret_bf16, [0, 0])
 
-            with amp.bf16_guard():
+            with amp.bf16.bf16_guard():
                 ret_fp32bf16 = layers.elementwise_add(t, tt)
                 ret_fp32bf16 = layers.elementwise_mul(ret_fp32bf16, t)
                 ret_fp32bf16 = layers.reshape(ret_fp32bf16, [0, 0])
@@ -103,7 +103,7 @@ class TestModelCastBF16(unittest.TestCase):
                     'tt_bf16': nn_bf16,
                 },
                 fetch_list=[ret_bf16, ret, ret_fp32bf16],
-                amp_fun=lambda prog: amp.rewrite_program_bf16(prog, use_bf16_guard=True))
+                amp_fun=lambda prog: amp.bf16.rewrite_program_bf16(prog))
 
         self.assertTrue(np.allclose(static_ret_bf16, static_ret, 1e-2))
         self.assertTrue(np.allclose(static_ret_bf16, ret_fp32bf16, 1e-2))
@@ -112,7 +112,7 @@ class TestModelCastBF16(unittest.TestCase):
             t = layers.data(name='t', shape=[size, size], dtype='float32')
             tt = layers.data(name='tt', shape=[size, size], dtype='float32')
 
-            with amp.bf16_guard():
+            with amp.bf16.bf16_guard():
                 ret = layers.elementwise_add(t, tt)
                 ret = layers.reshape(ret, [0, 0], act='elu')
                 ret = layers.elementwise_mul(ret, t)
@@ -122,17 +122,27 @@ class TestModelCastBF16(unittest.TestCase):
                 self.get_static_graph_result(
                     feed={'t': n, 'tt': nn},
                     fetch_list=[ret],
-                    amp_fun=lambda prog: amp.rewrite_program_bf16(
-                        prog,
-                        amp.AutoMixedPrecisionListsBF16(
-                            custom_fp32_varnames={'elementwise_add_0.tmp_0'}),
-                        use_bf16_guard=True
-                    )
+                    amp_fun=_amp_fun
                 )
         self.assertTrue(
             static_ret_bf16, np.ones(
                 [size, size], dtype='float32') * -1.1)
 
+    def test_graph_rewrite(self):
+        self._graph_common(lambda prog: amp.bf16.rewrite_program_bf16(
+            prog,
+            amp.bf16.AutoMixedPrecisionListsBF16(
+                custom_fp32_varnames={'elementwise_add_0.tmp_0'}),
+        ))
+
+    def test_graph_cast(self):
+        self._graph_common(lambda prog: amp.bf16.cast_model_to_bf16(
+            prog,
+            amp.bf16.AutoMixedPrecisionListsBF16(
+                custom_fp32_list={'elementwise_mul'}),
+            use_bf16_guard=True
+        ))
+
 
 if __name__ == '__main__':
     unittest.main()

python/paddle/fluid/layers/nn.py

@@ -332,7 +332,8 @@ def fc(input,
         for i, input_x in enumerate(input):
             check_type(input_x, 'input[' + str(i) + ']', Variable, 'fc')
     dtype = helper.input_dtype()
-    check_dtype(dtype, 'input', ['float16', 'float32', 'float64'], 'fc')
+    check_dtype(dtype, 'input', ['float16', 'uint16', 'float32', 'float64'],
+                'fc')
     mul_results = []
     for input_var, param_attr in helper.iter_inputs_and_params():
         input_shape = input_var.shape

python/paddle/fluid/layers/tensor.py

@@ -582,10 +582,9 @@ def assign(input, output=None):
         input = numpy.array(input)
 
     if isinstance(input, Variable):
-        check_dtype(
-            input.dtype, 'input',
-            ['float16', 'float32', 'float64', 'int32', 'int64', 'bool'],
-            'assign', '(When the type of input in assign is Variable.)')
+        check_dtype(input.dtype, 'input', [
+            'float16', 'uint16', 'float32', 'float64', 'int32', 'int64', 'bool'
+        ], 'assign', '(When the type of input in assign is Variable.)')
         if output is None:
             output = helper.create_variable_for_type_inference(
                 dtype=input.dtype)

python/paddle/fluid/tests/book/test_fit_a_line.py

@@ -16,6 +16,8 @@ from __future__ import print_function
 
 import paddle
 import paddle.fluid as fluid
+import paddle.static.amp as amp
+
 import contextlib
 import numpy
 import unittest
@@ -26,19 +28,34 @@ import os
 paddle.enable_static()
 
 
-def train(use_cuda, save_dirname, is_local, use_bf16):
+def train(use_cuda, save_dirname, is_local, use_bf16, pure_bf16):
     x = fluid.layers.data(name='x', shape=[13], dtype='float32')
-
-    y_predict = fluid.layers.fc(input=x, size=1, act=None)
-
     y = fluid.layers.data(name='y', shape=[1], dtype='float32')
 
-    cost = fluid.layers.square_error_cost(input=y_predict, label=y)
-    avg_cost = fluid.layers.mean(cost)
+    if use_bf16:
+        if not pure_bf16:
+            with amp.bf16.bf16_guard():
+                y_predict = fluid.layers.fc(input=x, size=1, act=None)
+            cost = fluid.layers.square_error_cost(input=y_predict, label=y)
+            avg_cost = fluid.layers.mean(cost)
+        else:
+            y_predict = fluid.layers.fc(input=x, size=1, act=None)
+            with amp.bf16.bf16_guard():
+                cost = fluid.layers.square_error_cost(input=y_predict, label=y)
+                avg_cost = fluid.layers.mean(cost)
+    else:
+        y_predict = fluid.layers.fc(input=x, size=1, act=None)
+        cost = fluid.layers.square_error_cost(input=y_predict, label=y)
+        avg_cost = fluid.layers.mean(cost)
 
     sgd_optimizer = fluid.optimizer.SGD(learning_rate=0.001)
+
     if use_bf16:
-        paddle.static.amp.rewrite_program_bf16(fluid.default_main_program())
+        sgd_optimizer = amp.bf16.decorate_bf16(
+            sgd_optimizer,
+            amp_lists=amp.bf16.AutoMixedPrecisionListsBF16(),
+            use_bf16_guard=False,
+            use_pure_bf16=pure_bf16)
     sgd_optimizer.minimize(avg_cost)
 
     BATCH_SIZE = 20
@@ -54,6 +71,10 @@ def train(use_cuda, save_dirname, is_local, use_bf16):
     def train_loop(main_program):
         feeder = fluid.DataFeeder(place=place, feed_list=[x, y])
         exe.run(fluid.default_startup_program())
+        test_prog = main_program.clone(for_test=True)
+        if pure_bf16:
+            sgd_optimizer.amp_init(
+                exe.place, test_program=test_prog, use_bf16_test=True)
 
         PASS_NUM = 100
         for pass_id in range(PASS_NUM):
@@ -61,9 +82,8 @@ def train(use_cuda, save_dirname, is_local, use_bf16):
                 avg_loss_value, = exe.run(main_program,
                                           feed=feeder.feed(data),
                                           fetch_list=[avg_cost])
-                print(avg_loss_value)
-                if avg_loss_value[0] < 10.0:
-                    if save_dirname is not None:
+                if avg_loss_value[0] < 10.0 or pure_bf16:
+                    if save_dirname is not None and not pure_bf16:
                         fluid.io.save_inference_model(save_dirname, ['x'],
                                                       [y_predict], exe)
                     return
@@ -97,7 +117,7 @@ def train(use_cuda, save_dirname, is_local, use_bf16):
             train_loop(t.get_trainer_program())
 
 
-def infer(use_cuda, save_dirname=None):
+def infer(use_cuda, save_dirname=None, use_bf16=False):
     if save_dirname is None:
         return
 
@@ -135,7 +155,7 @@ def infer(use_cuda, save_dirname=None):
         print("ground truth: ", test_label)
 
 
-def main(use_cuda, is_local=True, use_bf16=False):
+def main(use_cuda, is_local=True, use_bf16=False, pure_bf16=False):
     if use_cuda and not fluid.core.is_compiled_with_cuda():
         return
 
@@ -145,11 +165,22 @@ def main(use_cuda, is_local=True, use_bf16=False):
     # Directory for saving the trained model
     save_dirname = "fit_a_line.inference.model"
 
-    train(use_cuda, save_dirname, is_local, use_bf16)
-    infer(use_cuda, save_dirname)
+    train(use_cuda, save_dirname, is_local, use_bf16, pure_bf16)
+    infer(use_cuda, save_dirname, use_bf16)
+
+
+class TestFitALineBase(unittest.TestCase):
+    @contextlib.contextmanager
+    def program_scope_guard(self):
+        prog = fluid.Program()
+        startup_prog = fluid.Program()
+        scope = fluid.core.Scope()
+        with fluid.scope_guard(scope):
+            with fluid.program_guard(prog, startup_prog):
+                yield
 
 
-class TestFitALine(unittest.TestCase):
+class TestFitALine(TestFitALineBase):
     def test_cpu(self):
         with self.program_scope_guard():
             main(use_cuda=False)
@@ -158,20 +189,17 @@ class TestFitALine(unittest.TestCase):
         with self.program_scope_guard():
             main(use_cuda=True)
 
-    @unittest.skipIf(not fluid.core.supports_bfloat16(),
-                     "place does not support BF16 evaluation")
+
+@unittest.skipIf(not fluid.core.supports_bfloat16(),
+                 "place does not support BF16 evaluation")
+class TestFitALineBF16(TestFitALineBase):
     def test_bf16(self):
         with self.program_scope_guard():
             main(use_cuda=False, use_bf16=True)
 
-    @contextlib.contextmanager
-    def program_scope_guard(self):
-        prog = fluid.Program()
-        startup_prog = fluid.Program()
-        scope = fluid.core.Scope()
-        with fluid.scope_guard(scope):
-            with fluid.program_guard(prog, startup_prog):
-                yield
+    def test_pure_bf16(self):
+        with self.program_scope_guard():
+            main(use_cuda=False, use_bf16=True, pure_bf16=True)
 
 
 if __name__ == '__main__':

python/paddle/fluid/tests/book/test_word2vec_book.py

@@ -44,7 +44,8 @@ def train(target,
           is_parallel,
           save_dirname,
           is_local=True,
-          use_bf16=False):
+          use_bf16=False,
+          pure_bf16=False):
     PASS_NUM = 100
     EMBED_SIZE = 32
     HIDDEN_SIZE = 256
@@ -107,7 +108,13 @@ def train(target,
 
     sgd_optimizer = fluid.optimizer.SGD(learning_rate=0.001)
     if use_bf16:
-        paddle.static.amp.rewrite_program_bf16(fluid.default_main_program())
+        sgd_optimizer = paddle.static.amp.bf16.decorate_bf16(
+            sgd_optimizer,
+            amp_lists=paddle.static.amp.bf16.AutoMixedPrecisionListsBF16(
+                custom_fp32_list={'softmax', 'concat'}, ),
+            use_bf16_guard=False,
+            use_pure_bf16=pure_bf16)
+
     sgd_optimizer.minimize(avg_cost)
 
     train_reader = paddle.batch(
@@ -121,6 +128,8 @@ def train(target,
 
     def train_loop(main_program):
         exe.run(fluid.default_startup_program())
+        if pure_bf16:
+            sgd_optimizer.amp_init(exe.place)
 
         for pass_id in range(PASS_NUM):
             for data in train_reader():
@@ -128,7 +137,7 @@ def train(target,
                                       feed=feeder.feed(data),
                                       fetch_list=[avg_cost])
                 if avg_cost_np[0] < 5.0:
-                    if save_dirname is not None:
+                    if save_dirname is not None and not pure_bf16:
                         fluid.io.save_inference_model(save_dirname, [
                             'firstw', 'secondw', 'thirdw', 'forthw'
                         ], [predict_word], exe)
@@ -246,7 +255,7 @@ def infer(target, save_dirname=None):
             assert np.isclose(a, b, rtol=5e-5), "a: {}, b: {}".format(a, b)
 
 
-def main(target, is_sparse, is_parallel, use_bf16):
+def main(target, is_sparse, is_parallel, use_bf16, pure_bf16):
     if target == "cuda" and not fluid.core.is_compiled_with_cuda():
         return
     if target == "xpu" and not fluid.core.is_compiled_with_xpu():
@@ -265,7 +274,13 @@ def main(target, is_sparse, is_parallel, use_bf16):
         # so only inference is turned on.
         train("cpu", is_sparse, is_parallel, save_dirname)
     else:
-        train(target, is_sparse, is_parallel, save_dirname, use_bf16=use_bf16)
+        train(
+            target,
+            is_sparse,
+            is_parallel,
+            save_dirname,
+            use_bf16=use_bf16,
+            pure_bf16=pure_bf16)
     infer(target, save_dirname)
 
 
@@ -278,10 +293,15 @@ class W2VTest(unittest.TestCase):
     pass
 
 
-def inject_test_method(target, is_sparse, is_parallel, use_bf16=False):
+def inject_test_method(target,
+                       is_sparse,
+                       is_parallel,
+                       use_bf16=False,
+                       pure_bf16=False):
     fn_name = "test_{0}_{1}_{2}{3}".format(target, "sparse"
                                            if is_sparse else "dense", "parallel"
-                                           if is_parallel else "normal", "_bf16"
+                                           if is_parallel else "normal",
+                                           "_purebf16" if pure_bf16 else "_bf16"
                                            if use_bf16 else "")
 
     def __impl__(*args, **kwargs):
@@ -290,7 +310,7 @@ def inject_test_method(target, is_sparse, is_parallel, use_bf16=False):
         scope = fluid.core.Scope()
         with fluid.scope_guard(scope):
             with fluid.program_guard(prog, startup_prog):
-                main(target, is_sparse, is_parallel, use_bf16)
+                main(target, is_sparse, is_parallel, use_bf16, pure_bf16)
 
     if (not fluid.core.is_compiled_with_cuda() or
             target == "cuda") and is_sparse:
@@ -307,7 +327,8 @@ for target in ("cuda", "cpu", "xpu"):
     for is_sparse in (False, True):
         for is_parallel in (False, ):
             inject_test_method(target, is_sparse, is_parallel)
-inject_test_method("cpu", False, False, use_bf16=True)
+inject_test_method("cpu", False, False, True)
+inject_test_method("cpu", False, False, True, True)
 
 if __name__ == '__main__':
     unittest.main()

python/paddle/fluid/tests/unittests/test_optimizer_grad.py

@@ -64,7 +64,7 @@ class SimpleNetWithCond(object):
 
         return grads
 
-    def build_net(self, cond_i):
+    def build_net(self, cond_i, use_bf16=False):
         """
         pseudo code:
             sum_xy = x + y
@@ -122,13 +122,22 @@ class SimpleNetWithCond(object):
         sum_cond = fluid.layers.cond(cond_i > 1.0, cond_true, cond_false)
         sum_all = fluid.layers.sum([sum_xy, sub_yz, sum_cond])
         mean_out = fluid.layers.mean(sum_all)
+        if use_bf16:
+            import paddle.static.amp as amp
+            self.optimizer = amp.bf16.decorate_bf16(
+                self.optimizer,
+                amp_lists=amp.bf16.AutoMixedPrecisionListsBF16(
+                    custom_fp32_list={'elementwise_add'}),
+                use_bf16_guard=False,
+                use_pure_bf16=True)
+
         self.optimizer.minimize(mean_out)
 
         fetch_list = ["param_x", "param_z"] if self.y_no_grad else [
             "param_x", "param_y", "param_z"
         ]
         fetch_list += [_append_grad_suffix_(param) for param in fetch_list]
-        return fetch_list
+        return fetch_list, self.optimizer
 
 
 class TestOptimizer(unittest.TestCase):
@@ -180,7 +189,7 @@ class TestOptimizer(unittest.TestCase):
         for key in ['x', 'y', 'z']:
             self.param_attr[key] = self.attr.copy()
 
-    def _check_grads(self):
+    def _check_grads(self, use_bf16=False):
         """
         main logic code to check the validity of apply_optimize.
         """
@@ -204,10 +213,16 @@ class TestOptimizer(unittest.TestCase):
                                 lambda: dict())
                             test_net = self.NetClass(self.optimizer, param_lr,
                                                      y_no_grad)
-                            fetch_list = test_net.build_net(cond_i)
+                            fetch_list, decorated_optimizer = test_net.build_net(
+                                cond_i, use_bf16)
+                            if use_bf16:
+                                self.optimizer = decorated_optimizer
 
                             exe = fluid.Executor(place)
                             exe.run(init_program)
+                            if use_bf16:
+                                self.optimizer.amp_init(exe.place)
+
                             # Train 2 steps to check validity
                             for batch_i in range(2):
 
@@ -222,6 +237,15 @@ class TestOptimizer(unittest.TestCase):
                                                                param_grads[i])
 
 
+@unittest.skipIf(not fluid.core.supports_bfloat16(),
+                 "place does not support BF16 evaluation")
+class TestSGDOptimizer(TestOptimizer):
+    def test_optimizer_multiblock_except(self):
+        with self.assertRaisesRegexp(ValueError,
+                                     "var param_y not in this block"):
+            self._check_grads(use_bf16=True)
+
+
 class TestAdamOptimizer(TestOptimizer):
     """
     inherit TestOptimizer and shall override two functions as follows:

python/paddle/static/amp/__init__.py

@@ -18,7 +18,4 @@ from ...fluid.contrib.mixed_precision import AutoMixedPrecisionLists  # noqa: F4
 from ...fluid.contrib.mixed_precision import fp16_guard  # noqa: F401
 from ...fluid.contrib.mixed_precision import cast_model_to_fp16  # noqa: F401
 from ...fluid.contrib.mixed_precision import cast_parameters_to_fp16  # noqa: F401
-from ...fluid.contrib.mixed_precision import AutoMixedPrecisionListsBF16  # noqa: F401
-from ...fluid.contrib.mixed_precision import bf16_guard  # noqa: F401
-from ...fluid.contrib.mixed_precision import rewrite_program_bf16  # noqa: F401
-from ...fluid.contrib.mixed_precision import convert_float_to_uint16  # noqa: F401
+from ...fluid.contrib.mixed_precision import bf16  # noqa: F401