def apply_gradients(self, grads_and_vars, global_step=None, name=None):
summed_grads_and_vars = []
for (grad, var) in grads_and_vars:
if grad is None:
summed_grads_and_vars.append((grad, var))
else:
with ops.colocate_with(grad):
# gradient accumulation
if self._gradients_to_accumulate > 1 and not self._pipelining:
grad = gen_poputil_ops.ipu_stateful_gradient_accumulate(
grad / self._gradients_to_accumulate,
num_mini_batches=self._gradients_to_accumulate)
# replication
if self._replicas > 1:
grad = gen_poputil_ops.ipu_replication_normalise(
cross_replica_ops.cross_replica_sum(grad))
grad = math_ops.cast(grad, var.dtype)
summed_grads_and_vars.append((grad, var))
if self._pipelining:
# can do weight decay here as apply_gradients is only called on last accumulation step
summed_grads_and_vars = self.add_WD(summed_grads_and_vars)
ret = self._optimizer.apply_gradients(summed_grads_and_vars,
global_step, name)
if self._sharded:
sharding.propagate_sharding(ops.get_default_graph())
return ret
def grad_fn(grad, param, m, v):
if self.add_cross_replica_sums:
grad = cross_replica_ops.cross_replica_sum(grad)
cast_grad = tf.cast(grad, dtype=tf.float32)
cast_grad = cast_grad / self.loss_scaling
# Standard Adam update.
next_m = (tf.multiply(self.beta_1, m) +
tf.multiply(1.0 - self.beta_1, cast_grad))
next_v = (tf.multiply(self.beta_2, v) +
tf.multiply(1.0 - self.beta_2, tf.square(cast_grad)))
update = tf.cast(next_m / (tf.sqrt(next_v) + self.epsilon),
param.dtype)
# Just adding the square of the weights to the loss function is *not*
# the correct way of using L2 regularization/weight decay with Adam,
# since that will interact with the m and v parameters in strange ways.
#
# Instead we want to decay the weights in a manner that doesn't interact
# with the m/v parameters. This is equivalent to adding the square
# of the weights to the loss with plain (non-momentum) SGD.
if self._do_use_weight_decay(param_name):
update += self.weight_decay_rate * param
update_with_lr = self.learning_rate * update
next_param = param - update_with_lr
return next_param, next_v, next_m
def apply_gradients(self, grads_and_vars, global_step=None, name=None):
"""Apply gradients to variables.
Calls popops_cross_replica_sum.cross_replica_sum() to sum gradient
contributions across replicas, and then applies the real optimizer.
Args:
grads_and_vars: List of (gradient, variable) pairs as returned by
compute_gradients().
global_step: Optional Variable to increment by one after the
variables have been updated.
name: Optional name for the returned operation. Default to the
name passed to the Optimizer constructor.
Returns:
An `Operation` that applies the gradients. If `global_step` was not None,
that operation also increments `global_step`.
Raises:
ValueError: If the grads_and_vars is malformed.
"""
summed_grads_and_vars = []
for (grad, var) in grads_and_vars:
if grad is None:
summed_grads_and_vars.append((grad, var))
else:
with ops.colocate_with(grad):
summed_grads_and_vars.append(
(gen_poputil_ops.ipu_replication_normalise(
cross_replica_ops.cross_replica_sum(grad)), var))
return self._opt.apply_gradients(summed_grads_and_vars, global_step,
name)
def comp_fn():
def body(total_accuracy, image, label):
accuracy = validation_graph_builder(model, image, label, opts)
return total_accuracy + (tf.cast(accuracy, tf.float32) / opts["validation_batches_per_step"])
accuracy = loops.repeat(int(opts["validation_batches_per_step"]),
body, [tf.constant(0, tf.float32)], valid_iterator)
if opts['replicas'] > 1:
accuracy = cross_replica_ops.cross_replica_sum(accuracy) / (opts['replicas']*opts['shards'])
return accuracy
def _reduce_to(self, reduce_op, value, destinations):
del destinations
if not _is_current_device_ipu():
return value
if reduce_op not in (reduce_util.ReduceOp.SUM,
reduce_util.ReduceOp.MEAN):
raise ValueError("Unsupported reduce op: {}".format(reduce_op))
result = cross_replica_ops.cross_replica_sum(value)
if reduce_op == reduce_util.ReduceOp.MEAN:
result = gen_poputil_ops.ipu_replication_normalise(result)
return result
def _reduce_to(self, reduce_op, value, destinations):
del destinations
if not _is_current_device_ipu():
# If not on IPU, use Horovod for the reduction.
return hvd_allreduce(value, op=_to_horovod_op(reduce_op))
# On IPU we do a compiled reduction with GCL.
if reduce_op not in (reduce_util.ReduceOp.SUM,
reduce_util.ReduceOp.MEAN):
raise ValueError("Unsupported reduce op: {}".format(reduce_op))
result = cross_replica_ops.cross_replica_sum(value)
if reduce_op == reduce_util.ReduceOp.MEAN:
result = gen_poputil_ops.ipu_replication_normalise(result)
return result
def apply_gradients(self, grads_and_vars, global_step=None, name=None):
summed_grads_and_vars = []
for (grad, var) in grads_and_vars:
if grad is None:
summed_grads_and_vars.append((grad, var))
else:
with ops.colocate_with(grad):
# gradient accumulation
if self._gradient_accumulation_count > 1 and not self._pipelining:
grad = gen_poputil_ops.ipu_stateful_gradient_accumulate(
grad,
num_mini_batches=self._gradient_accumulation_count)
# replication
if self._replicas > 1:
grad = gen_poputil_ops.ipu_replication_normalise(
cross_replica_ops.cross_replica_sum(grad))
# distribution with IPUMultiWorkerStrategy needs additional normalisation by the number of workers
if isinstance(
distribute.get_strategy(),
ipu_multi_worker_strategy.IPUMultiWorkerStrategy):
grad /= distribute.get_strategy().num_replicas_in_sync
grad = math_ops.cast(grad, var.dtype)
summed_grads_and_vars.append((grad, var))
if self._pipelining:
# can do weight decay here as apply_gradients is only called on last accumulation step
summed_grads_and_vars = self.add_WD(summed_grads_and_vars)
if self._grad_scale != 1.0:
# don't rescale batch norm moving average statistics as they are not affected by loss scaling
summed_grads_and_vars = [
(grad, var) if 'batch_norm/moving_' in var.name else
(grad / self._grad_scale, var)
for grad, var in summed_grads_and_vars
]
ret = self._optimizer.apply_gradients(summed_grads_and_vars,
global_step, name)
if self._sharded:
sharding.propagate_sharding(ops.get_default_graph())
return ret
def comp_fn():
def body(total_accuracy, data_dict):
accuracy = validation_graph_builder(model, data_dict, opts)
if opts['latency']:
timestamp_enqueue = timestamp_queue.enqueue(
data_dict['timestamp'])
return (total_accuracy +
(tf.cast(accuracy, tf.float32) /
opts["validation_batches_per_step"]),
timestamp_enqueue)
else:
return total_accuracy + (
tf.cast(accuracy, tf.float32) /
opts["validation_batches_per_step"])
accuracy = loops.repeat(
int(opts["validation_batches_per_step"]), body,
[tf.constant(0, tf.float32)], valid_iterator)
if opts['total_replicas'] * opts['shards'] > 1 and not opts.get(
'inference', False):
accuracy = cross_replica_ops.cross_replica_sum(
accuracy) / (opts['total_replicas'] * opts['shards'])
return accuracy
def grad_fn(grad, param, m, v):
if self.add_cross_replica_sums:
grad = cross_replica_ops.cross_replica_sum(grad)
# We convert the gradient to fp32 and we rescale it
cast_grad = tf.cast(grad, dtype=tf.float32)
cast_grad = cast_grad / self.loss_scaling
if self.use_nvlamb:
# We de normalize the gradients
cast_grad = cast_grad * self.clipping_value / global_norm
# Standard Adam update.
next_m = (tf.multiply(self.beta_1, m) +
tf.multiply(1.0 - self.beta_1, cast_grad))
next_v = (tf.multiply(self.beta_2, v) +
tf.multiply(1.0 - self.beta_2, tf.square(cast_grad)))
# Beta scaling of momentum and velocity
if self.debiasing:
m_hat = next_m / (1.0 - tf.pow(
self.beta_1, tf.cast(self.step, dtype=tf.float32))) # x10
v_hat = next_v / (1.0 - tf.pow(
self.beta_2, tf.cast(self.step, dtype=tf.float32))
) # x1000
else:
m_hat = next_m
v_hat = next_v
# TODO: Check if it is possible to convert to fp16 here.
# m_hat = tf.cast(m_hat, dtype = tf.float16)
# v_hat = tf.cast(v_hat, dtype = tf.float16)
update = m_hat / (tf.sqrt(tf.math.abs(v_hat)) +
tf.cast(self.epsilon, dtype=v_hat.dtype))
# Just adding the square of the weights to the loss function is *not*
# the correct way of using L2 regularization/weight decay with Adam,
# since that will interact with the m and v parameters in strange ways.
#
# Instead we want ot decay the weights in a manner that doesn't interact
# with the m/v parameters. This is equivalent to adding the square
# of the weights to the loss with plain (non-momentum) SGD.
if self._do_use_weight_decay(param_name):
update += tf.cast(self.weight_decay_rate,
dtype=update.dtype) * tf.cast(
param, dtype=update.dtype)
if 'qkv' in param_name:
# We reshape the parameters
reshaped_param = self.forward_transform(param)
reshaped_update = self.forward_transform(update)
else:
reshaped_param = tf.reshape(param, [-1])
reshaped_update = tf.reshape(update, [-1])
# Norms are then computed in fp32
w_norm = linalg_ops.norm(tf.cast(reshaped_param,
dtype=tf.float32),
ord=2,
axis=-1)
u_norm = linalg_ops.norm(reshaped_update, ord=2, axis=-1)
reshaped_update = tf.cast(reshaped_update, dtype=self.target_type)
if self.weight_clip:
w_norm = tf.math.minimum(
w_norm, tf.cast(self.weight_clip, dtype=w_norm.dtype))
# We set the ratio to 1 if either the w norm and the u norms are 0
ratio = array_ops.where(
math_ops.greater(w_norm, 0),
array_ops.where(
math_ops.greater(u_norm, 0),
(tf.cast(w_norm, dtype=tf.float32) / u_norm),
tf.constant(1.0, dtype=tf.float32, shape=w_norm.shape)),
tf.constant(1.0, dtype=tf.float32, shape=w_norm.shape))
# We reshape the ration in order to be broadcastable
ratio = tf.reshape(ratio, shape=ratio.shape.as_list() + [1])
# We combine the learning rate and the ratio at fp32
ratio = ratio * tf.cast(self.learning_rate, dtype=tf.float32)
# We now downcast to do the next operation
# If the scaledd is present we do not need this operation
ratio = tf.cast(ratio, dtype=tf.float16)
update_with_lr = ratio * reshaped_update
# Backward transform to the same as param
if 'qkv' in param_name:
update_with_lr = self.backward_transform(update_with_lr)
else:
update_with_lr = tf.reshape(update_with_lr, shape=param.shape)
update_with_lr = tf.cast(update_with_lr, dtype=param.dtype)
next_param = param - update_with_lr
return next_param, next_m, next_v
def my_body(acc, x):
index = math_ops.cast(replication_index(), np.float32) + 1.0
acc += cross_replica_sum(index)
acc += x * x
return acc, outfeed.enqueue(index)