[Nengo-DL]: Cannot create a tensor proto whose content is larger than 2GB

Deep Learning
1

One of the underlying data structures of Tensorflow (protocol buffers) are capped at 2GB. On certain large networks, this makes nengo_dl.Simulator fail where nengo.Simulator and nengo_ocl.Simulator succeed.

This issue and some workarounds are documented

For a nengo frontend user, it is hard to implement those workarounds fairly deep within the backend. Am I missing some config option to allow the use of >2GB connections? If so, it might benefit from some documentation in the nengo or at least nengo_dl docs. If not, perhaps that option should exist, or perhaps nengo_dl could catch this exception and rectify it at runtime.

Input: (you will need >10GB RAM to make it to the exception in question)

import numpy as np
import nengo
import nengo_dl

transform = np.random.normal(size=(3*10**4, 3*10**4))  # Fails
# transform = np.zeros((3*10**4, 3*10**4))  # Works
print(transform.nbytes / 1e9, 'GB')  # 7.2 GB

with nengo.Network() as net:
    ens = nengo.Ensemble(transform.shape[0], 1)
    nengo.Connection(ens.neurons, ens.neurons, transform=transform)
sim = nengo_dl.Simulator(net)

Output:

7.2 GB
Build finished in 0:00:01                                                      
Optimization finished in 0:00:00                                               
|       #                 Constructing graph                          | 0:00:00
---------------------------------------------------------------------------
ValueError                                Traceback (most recent call last)
~/.local/lib/python3.8/site-packages/tensorflow/python/framework/op_def_library.py in _apply_op_helper(op_type_name, name, **keywords)
    464         try:
--> 465           values = ops.convert_to_tensor(
    466               values,

~/.local/lib/python3.8/site-packages/tensorflow/python/framework/ops.py in convert_to_tensor(value, dtype, name, as_ref, preferred_dtype, dtype_hint, ctx, accepted_result_types)
   1340     if ret is None:
-> 1341       ret = conversion_func(value, dtype=dtype, name=name, as_ref=as_ref)
   1342 

~/.local/lib/python3.8/site-packages/tensorflow/python/framework/tensor_conversion_registry.py in _default_conversion_function(***failed resolving arguments***)
     51   del as_ref  # Unused.
---> 52   return constant_op.constant(value, dtype, name=name)
     53 

~/.local/lib/python3.8/site-packages/tensorflow/python/framework/constant_op.py in constant(value, dtype, shape, name)
    260   """
--> 261   return _constant_impl(value, dtype, shape, name, verify_shape=False,
    262                         allow_broadcast=True)

~/.local/lib/python3.8/site-packages/tensorflow/python/framework/constant_op.py in _constant_impl(value, dtype, shape, name, verify_shape, allow_broadcast)
    297   tensor_value.tensor.CopyFrom(
--> 298       tensor_util.make_tensor_proto(
    299           value, dtype=dtype, shape=shape, verify_shape=verify_shape,

~/.local/lib/python3.8/site-packages/tensorflow/python/framework/tensor_util.py in make_tensor_proto(values, dtype, shape, verify_shape, allow_broadcast)
    520     if nparray.size * nparray.itemsize >= (1 << 31):
--> 521       raise ValueError(
    522           "Cannot create a tensor proto whose content is larger than 2GB.")

ValueError: Cannot create a tensor proto whose content is larger than 2GB.

During handling of the above exception, another exception occurred:

ValueError                                Traceback (most recent call last)
~/.local/lib/python3.8/site-packages/tensorflow/python/framework/op_def_library.py in _apply_op_helper(op_type_name, name, **keywords)
    482           try:
--> 483             observed = ops.convert_to_tensor(
    484                 values, as_ref=input_arg.is_ref).dtype.name

~/.local/lib/python3.8/site-packages/tensorflow/python/framework/ops.py in convert_to_tensor(value, dtype, name, as_ref, preferred_dtype, dtype_hint, ctx, accepted_result_types)
   1340     if ret is None:
-> 1341       ret = conversion_func(value, dtype=dtype, name=name, as_ref=as_ref)
   1342 

~/.local/lib/python3.8/site-packages/tensorflow/python/framework/tensor_conversion_registry.py in _default_conversion_function(***failed resolving arguments***)
     51   del as_ref  # Unused.
---> 52   return constant_op.constant(value, dtype, name=name)
     53 

~/.local/lib/python3.8/site-packages/tensorflow/python/framework/constant_op.py in constant(value, dtype, shape, name)
    260   """
--> 261   return _constant_impl(value, dtype, shape, name, verify_shape=False,
    262                         allow_broadcast=True)

~/.local/lib/python3.8/site-packages/tensorflow/python/framework/constant_op.py in _constant_impl(value, dtype, shape, name, verify_shape, allow_broadcast)
    297   tensor_value.tensor.CopyFrom(
--> 298       tensor_util.make_tensor_proto(
    299           value, dtype=dtype, shape=shape, verify_shape=verify_shape,

~/.local/lib/python3.8/site-packages/tensorflow/python/framework/tensor_util.py in make_tensor_proto(values, dtype, shape, verify_shape, allow_broadcast)
    520     if nparray.size * nparray.itemsize >= (1 << 31):
--> 521       raise ValueError(
    522           "Cannot create a tensor proto whose content is larger than 2GB.")

ValueError: Cannot create a tensor proto whose content is larger than 2GB.

During handling of the above exception, another exception occurred:

ValueError                                Traceback (most recent call last)
<ipython-input-1-6a480743f0ee> in <module>
     11     ens = nengo.Ensemble(transform.shape[0], 1)
     12     nengo.Connection(ens.neurons, ens.neurons, transform=transform)
---> 13 sim = nengo_dl.Simulator(net)

~/.local/lib/python3.8/site-packages/nengo_dl/simulator.py in __init__(self, network, dt, seed, model, device, unroll_simulation, minibatch_size, progress_bar)
    533         ) as progress:
    534             self.graph = tf.Graph()
--> 535             self._build_keras(progress)
    536 
    537         # initialize sim attributes

~/.local/lib/python3.8/site-packages/nengo/utils/magic.py in __call__(self, *args, **kwargs)
    179                 return self.wrapper(wrapped, instance, args, kwargs)
    180             else:
--> 181                 return self.wrapper(self.__wrapped__, self.instance, args, kwargs)
    182         else:
    183             instance = getattr(self.__wrapped__, "__self__", None)

~/.local/lib/python3.8/site-packages/nengo_dl/simulator.py in with_self(wrapped, instance, args, kwargs)
     56         instance.tensor_graph.device
     57     ):
---> 58         output = wrapped(*args, **kwargs)
     59     tf.keras.backend.set_floatx(keras_dtype)
     60 

~/.local/lib/python3.8/site-packages/nengo_dl/simulator.py in _build_keras(self, progress)
    558         inputs = list(self.node_inputs.values()) + [n_steps]
    559 
--> 560         outputs = self.tensor_graph(
    561             inputs,
    562             stateful=self.stateful,

~/.local/lib/python3.8/site-packages/tensorflow/python/keras/engine/base_layer.py in __call__(self, *args, **kwargs)
    895           # Build layer if applicable (if the `build` method has been
    896           # overridden).
--> 897           self._maybe_build(inputs)
    898           cast_inputs = self._maybe_cast_inputs(inputs)
    899 

~/.local/lib/python3.8/site-packages/tensorflow/python/keras/engine/base_layer.py in _maybe_build(self, inputs)
   2414         # operations.
   2415         with tf_utils.maybe_init_scope(self):
-> 2416           self.build(input_shapes)  # pylint:disable=not-callable
   2417       # We must set also ensure that the layer is marked as built, and the build
   2418       # shape is stored since user defined build functions may not be calling

~/.local/lib/python3.8/site-packages/nengo_dl/tensor_graph.py in build(self, input_shape)
    259         for sig_type in ("trainable", "non_trainable"):
    260             for k, v in self.base_arrays_init[sig_type].items():
--> 261                 initializer, shape, dtype = get_initializer(v)
    262                 assert initializer is not None  # params should never be set
    263                 self.base_params[k] = self.add_weight(

~/.local/lib/python3.8/site-packages/nengo_dl/tensor_graph.py in get_initializer(init_vals)
    237             else:
    238                 val = tf.concat(
--> 239                     [
    240                         tf.zeros(s, dtype)
    241                         if v is None

~/.local/lib/python3.8/site-packages/nengo_dl/tensor_graph.py in <listcomp>(.0)
    240                         tf.zeros(s, dtype)
    241                         if v is None
--> 242                         else tf.cast(tf.broadcast_to(v, s), dtype)
    243                         for v, s in zip(values, shapes)
    244                     ],

~/.local/lib/python3.8/site-packages/tensorflow/python/ops/gen_array_ops.py in broadcast_to(input, shape, name)
    827   # Add nodes to the TensorFlow graph.
    828   try:
--> 829     _, _, _op, _outputs = _op_def_library._apply_op_helper(
    830         "BroadcastTo", input=input, shape=shape, name=name)
    831   except (TypeError, ValueError):

~/.local/lib/python3.8/site-packages/tensorflow/python/framework/op_def_library.py in _apply_op_helper(op_type_name, name, **keywords)
    484                 values, as_ref=input_arg.is_ref).dtype.name
    485           except ValueError as err:
--> 486             raise ValueError(
    487                 "Tried to convert '%s' to a tensor and failed. Error: %s" %
    488                 (input_name, err))

ValueError: Tried to convert 'input' to a tensor and failed. Error: Cannot create a tensor proto whose content is larger than 2GB.
2

Unfortunately there isn’t really a way to work around this TensorFlow limitation in TensorFlow 2 (the method you link to, using placeholders to feed in values, only works in TensorFlow < 2.0, as TensorFlow 2 did away with the notion of placeholders).

However, I believe this issue should be resolved when we switch NengoDL to using TensorFlow’s eager-mode (which doesn’t have this 2GB limitation), rather than graph-mode. In the past eager-mode was significantly slower than graph-mode, but they have recently made speed improvements so we are planning to switch to eager-mode in the near future.

3

Sounds like you have a good plan to address it in the future. I am mostly right now interested in networks of sparsity ~1e-3 of the type in Watts & Strogatz, “Collective Dynamics of Small-World Networks,” Nature 393. 1998. In other words, a sliding scale from a ring (block off-diagonal) network to a random network.

These questions would really help me decide how to move forward with sparse networks:

  1. Can nengo_dl efficiently leverage the GPU for nengo.builder.transforms.Sparse transforms? These use CSR sparse matrices. [BTW, I don’t think nengo_ocl leverages the efficiency of this datatype]
  2. Suppose one decomposes the large, sparse network into multiple dense ensembles. Can nengo_dl efficiently leverage the GPU for a network with lots of ensembles? These use BSR sparse matrices.

Let me know if these would be more appropriate posed in a new forum thread.

Thanks for the response!

4

Yes, NengoDL has full support for sparse transforms on the GPU.

We actually used to automatically combine parallel dense matrices into a single, larger block-diagonal sparse matrix. However, after some experimentation we found that this was generally slower than just computing them individually, so we switched back to that. You always have the option to create the block-diagonal matrix yourself using a nengo.Sparse transform though if you want to see if it is faster for your use case. And as a sidenote, there are plans to add more performant sparse matrix implementations to TensorFlow in the nearish future (see RFC: CSRSparseMatrix by penpornk · Pull Request #246 · tensorflow/community · GitHub), which should speed all of this up!

5

Great! That’s very helpful.

I think my original question is answered, so we can mark this solved. I will go ahead and elevate to an issue, which can be closed when NengoDL switches to eager-mode (or that switch becomes a config option).

Issue: https://github.com/nengo/nengo-dl/issues/160