# Copyright 2022 Cerebras Systems.
#
# 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.
import math
import random
import numpy as np
import torch
import cerebras.pytorch as cstorch
import cerebras.pytorch.distributed as dist
from cerebras.pytorch.distributed.cluster_resolver import ClusterSpec, TaskSpec
[docs]def get_data_for_task(
task_id,
meta_data_values_cum_sum,
num_examples_per_task,
meta_data_values,
meta_data_filenames,
):
"""
Function to get distribute files with given number of examples such that each
distributed task has access to exactly the same number of examples
Args:
task_id (int): Integer id for a task.
meta_data_values_cum_sum (int): Cumulative sum of the file sizes in
lines from meta data file.
num_examples_per_task (int): Number of the examples specified per
slurm task. Equal to `batch_size` * `num_batch_per_task`.
meta_data_values (list[int]): List of the files sizes in lines in the
meta data file.
meta_data_filenames (list[str]): List with file names in the meta data
file.
Returns:
list of tuples of length 3. The tuple contains at
- index 0: filepath.
- index 1: number of examples to be considered for this task_id.
- index 2: start index in the file from where these
examples should be considered
The list represents the files that should be considered for this task_id.
"""
files_in_task = []
# file where the split starts
file_start_idx = np.min(
np.where(meta_data_values_cum_sum > task_id * num_examples_per_task)[0]
)
# Index in file from where the examples should be considered for this task
start_idx = (
task_id * num_examples_per_task
- meta_data_values_cum_sum[file_start_idx - 1]
# -1 since len(`meta_data_values_cum_sum`) = len(`meta_data_values`) + 1
)
# Number of examples to pick from this file.
# We do a `min` to handle a case where the file has
# examples > num_examples_per_task
num_examples = min(
meta_data_values[file_start_idx - 1] - start_idx,
num_examples_per_task,
)
files_in_task.append(
(
meta_data_filenames[file_start_idx - 1],
num_examples,
start_idx,
) # (file_path, num_examples, start_index)
)
if num_examples != num_examples_per_task:
# If the file has fewer number of examples than
# `num_examples_per_task`, continue through files
# till we reach our required number of examples.
indices = np.where(
meta_data_values_cum_sum > (task_id + 1) * num_examples_per_task
)[0]
if indices.size != 0:
file_end_idx = np.min(indices)
else:
file_end_idx = len(meta_data_values_cum_sum)
for i in range(file_start_idx + 1, file_end_idx):
files_in_task.append(
(
meta_data_filenames[i - 1],
meta_data_values[i - 1],
0,
) # (file_path, num_examples, start_index)
)
# If the number of examples needed to fulfill
# `num_examples_per_task`, falls in between a file
num_end_examples = (
task_id + 1
) * num_examples_per_task - meta_data_values_cum_sum[file_end_idx - 1]
if num_end_examples > 0:
files_in_task.append(
(
meta_data_filenames[file_end_idx - 1],
num_end_examples,
0,
) # (file_path, num_examples, start_index)
)
assert (
sum([num_examples for _, num_examples, _ in files_in_task])
== num_examples_per_task
), f"Incorrect number of examples in the split with task_id {task_id}"
return files_in_task
[docs]def is_distributed():
"""
Returns True if DDP is enabled.
"""
return (
torch.distributed.is_available() and torch.distributed.is_initialized()
)
[docs]def task_id():
if dist.is_streamer():
return dist.get_streaming_rank()
elif is_distributed():
return dist.get_rank()
else:
return 0
[docs]def num_tasks():
if dist.is_streamer():
return dist.num_streamers()
elif is_distributed():
return dist.get_world_size()
else:
return 1
[docs]def cluster_config():
"""
Returns (ClusterSpec, TaskSpec). The TaskSpec contains the following fields:
- rank: the global rank of the current worker
- local_rank: the rank of the current worker among workers who feed
the same system as the current worker
- wse_id: the index of the system that the current worker is
associated with
The ClusterSpec contains the following fields:
- tasks: a list of TaskSpecs for each task running on the cluster
- rank: the rank of the current process's task in the cluster
- num_csx: the number of CSX systems in the cluster
- num_workers_per_csx: the number of worker tasks per CSX
If the current job is running on GPU instead of CS system, then
the ranks and world sizes in the returned TaskSpec will be set to the GPU
rank and world size.
"""
if cstorch.use_cs() and dist.is_streamer():
cluster_spec = dist.service_resolver().cluster_spec
task_spec = cluster_spec.task()
return cluster_spec, task_spec
elif is_distributed():
task_spec = TaskSpec(
rank=dist.get_rank(),
local_rank=dist.get_rank(),
wse_id=0,
node_name="unknown",
)
cluster_spec = ClusterSpec(
[task_spec],
dist.get_rank(),
1,
dist.get_world_size(),
)
return cluster_spec, task_spec
else:
task_spec = TaskSpec(
rank=0, local_rank=0, wse_id=0, node_name="unknown"
)
cluster_spec = ClusterSpec([task_spec], 0, 1, 1)
return cluster_spec, task_spec
[docs]class ShardedSampler(torch.utils.data.Sampler):
"""
Modified from:
https://pytorch.org/docs/stable/_modules/torch/utils/data/distributed.html#DistributedSampler
Sampler that restricts data loading to a subset of the dataset.
Dataset is assumed to be of constant size.
Args:
dataset (torch.utils.data.Dataset): Dataset used for sampling.
shuffle (bool, optional): If `True` (default), sampler will shuffle
the indices.
seed (int, optional): Random seed used to shuffle the sampler if
:attr:`shuffle=True`. This number should be identical across all
processes in the distributed group. Default: `0`.
drop_last (bool, optional): If `True`, then the sampler will drop the
tail of the data to make it evenly divisible across the number of
replicas. If `False`, the sampler will add extra indices to make
the data evenly divisible across the replicas. Default: `False`.
"""
def __init__(self, dataset, shuffle=True, seed=None, drop_last=False):
self.num_tasks = num_tasks()
self.task_id = task_id()
self.dataset = dataset
self.dataset_len = len(self.dataset)
self.drop_last = drop_last
if cstorch.use_cs() and not self.drop_last:
raise ValueError(
"On CS2 we do not support unequal batch sizes so `drop_last` "
"must be set to `True`."
)
# If the dataset length is evenly divisible by # of replicas, then there
# is no need to drop any data, since the dataset will be split equally.
if self.drop_last and len(self.dataset) % self.num_tasks:
# Split to nearest available length that is evenly divisible.
# This is to ensure each task receives the same amount of data when
# using this sampler.
self.num_samples = len(self.dataset) // self.num_tasks
else:
self.num_samples = math.ceil(len(self.dataset) / self.num_tasks)
self.total_size = self.num_samples * self.num_tasks
self.shuffle = shuffle
self.seed = seed
self.indices = list(range(self.dataset_len))
if not self.drop_last:
# add extra samples to make it evenly divisible across tasks
padding_indices_size = self.total_size - self.dataset_len
# choose padding indices at random to reduce the chance of
# reusing samples.
random.seed(self.seed)
padding_indices = random.sample(self.indices, padding_indices_size)
self.indices += padding_indices
else:
# remove tail of data to make it evenly divisible.
self.indices = self.indices[: self.total_size]
assert len(self.indices) == self.total_size, (
f"Total `indices` after dropping/padding indices must be equal "
f"to `total_size` of the dataset. Received total indices: "
f"`{len(self.indices)}` and total size is: `{self.total_size}`."
)
def __iter__(self):
if self.shuffle:
random.seed(self.seed)
random.shuffle(self.indices)
# subsample
indices = self.indices[self.task_id : self.total_size : self.num_tasks]
assert len(indices) == self.num_samples, (
f"Total `indices` for tasks must be equal to `num_samples` in a "
f"task. Received total indices: `{len(indices)}` and samples in "
f"task are: `{self.num_samples}`."
)
yield from indices
def __len__(self):
return self.num_samples
[docs]def check_sharding_sanity(
examples_per_file,
batch_size,
num_workers,
drop_last,
):
"""Checks if with the given sharding, at least one batch is generated.
Note that this method is operating based on how `shard_and_shuffle_data` is
sharding the data across workers.
:param list examples_per_file: Total examples per file for this task.
:param int batch_size: Batch size of the model.
:param int num_workers: Number of workers to use in the dataloader.
:param bool drop_last: Boolean indicating whether the last incomplete batch
of the dataloader is dropped.
:raises ValueError: If no batches are generated with the given sharding.
"""
if drop_last is False:
return
if num_workers == 0:
total_samples = sum(examples_per_file)
if total_samples < batch_size:
raise ValueError(
f"Task {task_id()} only generates {total_samples}, which "
f"is fewer than a full batch of size {batch_size}. "
)
return
examples_per_worker = [0] * num_workers
for file_idx, examples_in_file in enumerate(examples_per_file):
worker_id = file_idx % num_workers
examples_per_worker[worker_id] += examples_in_file
max_examples = max(examples_per_worker)
if max_examples < batch_size:
raise ValueError(
f"Maximum number of samples generated in dataloader workers of "
f"task {task_id()} is {max_examples}. Since {max_examples} is less "
f"than batch size {batch_size} and `drop_last` is True, this task "
f"will end up not producing any samples. Please specify a fewer "
f"number of workers or tasks."
)
[docs]def shard_list_contiguous(input_list, worker_id, num_workers):
"""
Shards a list by splitting it into `num_workers` contiguous segments.
Only the `worker_id`th shard is returned. If the length of the list is
not divisible by the number of workers, the last worker will be assigned
all remainder elements.
Args:
input_list (list): list to shard into contiguous segments
worker_id (int): index of shard to return
num_workers (int): number of shards to create
Returns:
A sublist of contiguous elements (`worker_id`'s shard)
"""
assert num_workers <= len(input_list), (
f"Number of processes should be less than number of files, "
f"Got `num_workers` equal to {num_workers} and `num_files` equal to {len(input_list)}."
)
per_worker_num_files = len(input_list) // num_workers
if worker_id < num_workers - 1:
output_list = input_list[
(worker_id * per_worker_num_files) : (
(worker_id + 1) * per_worker_num_files
)
]
else:
output_list = input_list[(worker_id * per_worker_num_files) :]
return output_list
[docs]def shard_list_interleaved(input_list, worker_id, num_workers):
"""
Shards a list by assigning consecutive elements to alternating workers
(i.e. interleaving). If the length of the list is not divisible by the
number of workers, the remainder elements are spread across a subset
of the workers such that each worker in the subset receives 1 extra
element.
Args:
input_list (list): list to shard in an interleaved fashion
worker_id (int): index of shard to return
num_workers (int): number of shards to create
Returns:
`worker_id`'s shard (a subset of `input_list`).
"""
output_for_cur_worker = []
if num_workers != 0:
assert num_workers <= len(input_list), (
f"Number of processes should be less than number of files, "
f"Got `num_workers` equal to {num_workers} and `num_files` equal to {len(input_list)}."
)
# Gather files for the input worker based in the file index and
# number of workers.
for index, elm in enumerate(input_list):
if index % num_workers == worker_id:
output_for_cur_worker.append(elm)
else:
output_for_cur_worker = input_list
return output_for_cur_worker
[docs]def shard_list_of_chunks_contiguous(
input_list_of_chunks, worker_id, num_workers
):
"""
Shards a list of chunks by distributing contiguous segments of each chunk
across shards. If the chunk's length is not divisible by the
number of workers, the remainder elements are spread across a subset
of the workers such that each worker in the subset receives 1 extra
element.
Args:
input_list (list of tuples): list of chunks to shard. List should be of format
`[... (chunk_i, length_of_chunk_i), ...]`
worker_id (int): index of shard to return
num_workers (int): number of shards to create
Returns:
`worker_id`'s shard: a list of the same length as `input_list` of the
format: `[... (chunk_i, shard_start_index_i, shard_length_i), ...]`
"""
output_for_cur_worker = []
for elm, chunk_length in input_list_of_chunks:
# Try to evenly distribute chunk_length between workers
chunk_length_per_worker = [(chunk_length // num_workers)] * num_workers
for i in range(chunk_length % num_workers):
chunk_length_per_worker[i] += 1
assert sum(chunk_length_per_worker) == chunk_length
output_for_cur_worker.append(
(
elm,
(
sum(chunk_length_per_worker[:worker_id])
if worker_id > 0
else 0
), # Start index
chunk_length_per_worker[worker_id], # Length of data chunk
)
)
return output_for_cur_worker