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# Sphinx build info version 1
# This file hashes the configuration used when building these files. When it is not found, a full rebuild will be done.
config: b1d4f130b437b34669c086e08878ee12
tags: 645f666f9bcd5a90fca523b33c5a78b7
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97 changes: 97 additions & 0 deletions docs/_sources/advanced.rst.txt
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.. _hivemind_intermediate:

Training on unreliable mixed GPUs across the internet (Advanced)
================================================================

Reducing Communication By Overlapping Communication
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

We can reduce the impact of communication across all machines by overlapping communication with our training iterations. In short, we enable communication to happen
in the background of training.

Overlap Gradient and State Averaging
""""""""""""""""""""""""""""""""""""

When the target batch size is reached, all processes that are included in the step send gradients and model states to each other. By enabling some flags through
the strategy, communication can happen in the background. This allows training to continue (with slightly outdated weights) but provides us the means
to overlap communication with computation.

.. warning::
Enabling overlapping communication means convergence will slightly be affected.

.. note::
Enabling these flags means that you must pass in a ``scheduler_fn`` to the ``HivemindStrategy`` instead of relying on a scheduler from ``configure_optimizers``.
The optimizer is re-created by Hivemind, and as a result, the scheduler has to be re-created.

.. code-block:: python
import torch
from functools import partial
from pytorch_lightning import Trainer
from lightning_hivemind.strategy import HivemindStrategy
trainer = Trainer(
strategy=HivemindStrategy(
target_batch_size=8192,
delay_state_averaging=True,
delay_grad_averaging=True,
delay_optimizer_step=True,
offload_optimizer=True, # required to delay averaging
scheduler_fn=partial(torch.optim.lr_scheduler.ExponentialLR, gamma=...),
),
accelerator="gpu",
devices=1,
)
Reducing GPU Memory requirements by re-using buffers & CPU offloading
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

We can also offload the optimizer state to the CPU whilst re-using gradient buffers to reduce the memory requirement for machines.

Offloading Optimizer State to the CPU
"""""""""""""""""""""""""""""""""""""

Offloading the Optimizer state to the CPU works the same as Deepspeed Zero-stage-2-offload, where we save GPU memory by keeping all optimizer states on the CPU.

.. note::
Enabling these flags means that you must pass in a ``scheduler_fn`` to the ``HivemindStrategy`` instead of relying on a scheduler from ``configure_optimizers``.
The optimizer is re-created by Hivemind, and as a result, the scheduler has to be re-created.

We suggest enabling offloading and overlapping communication to hide the additional overhead from having to communicate with the CPU.

.. code-block:: python
import torch
from functools import partial
from pytorch_lightning import Trainer
from lightning_hivemind.strategy import HivemindStrategy
trainer = Trainer(
strategy=HivemindStrategy(
target_batch_size=8192,
offload_optimizer=True,
scheduler_fn=partial(torch.optim.lr_scheduler.ExponentialLR, gamma=...),
),
accelerator="gpu",
devices=1,
)
Re-using Gradient Buffers
"""""""""""""""""""""""""

By default, Hivemind accumulates gradients in a separate buffer. This means additional GPU memory is required to store gradients. You can enable re-using the model parameter gradient buffers by passing ``reuse_grad_buffers=True`` to the ``HivemindStrategy``.

.. warning::
The ``HivemindStrategy`` will override ``zero_grad`` in your ``LightningModule`` to have no effect. This is because gradients are accumulated in the model
and Hivemind manages when they need to be cleared.

.. code-block:: python
from pytorch_lightning import Trainer
from lightning_hivemind.strategy import HivemindStrategy
trainer = Trainer(
strategy=HivemindStrategy(target_batch_size=8192, reuse_grad_buffers=True), accelerator="gpu", devices=1
)
85 changes: 85 additions & 0 deletions docs/_sources/expert.rst.txt
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.. _hivemind_expert:

Training on unreliable mixed GPUs across the internet (Expert)
==============================================================

Using Compression to Optimize Communications
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

Below are some ways to reduce communication when training collaboratively. As the size of your model increase, bottlenecks in communication become more apparent.

Compress Gradients & State
""""""""""""""""""""""""""

Hivemind allows you to compress gradients and states before sending them to other machines. This helps reduce the communication overhead substantially when training across the internet.

Below, we enable Float16 compression, which compresses gradients and states to Float16 before sending it to other machines.

.. note::
Compressing gradients can affect convergence if you're lowering the precision (i.e training in Float32, but compressing gradients to FP16).

.. code-block:: python
from hivemind import Float16Compression
from pytorch_lightning import Trainer
from lightning_hivemind.strategy import HivemindStrategy
trainer = Trainer(
strategy=HivemindStrategy(
target_batch_size=target_batch_size,
grad_compression=Float16Compression(),
state_averaging_compression=Float16Compression(),
),
accelerator="gpu",
devices=1,
)
A slightly more advanced scheme is dynamic compression based on value size. Below, we enable 8-bit quantization for large numbers, and Float16 compression for small values, reducing communication bottlenecks even further.

Size Adaptive Compression has been used in a variety of Hivemind applications and has shown success, but does quantize gradients further, meaning we lose precision when compressing.

.. code-block:: python
from hivemind import Float16Compression, Uniform8BitQuantization
from pytorch_lightning import Trainer
from lightning_hivemind.strategy import HivemindStrategy
# compresses values above threshold with 8bit Quantization, lower with Float16
compression = SizeAdaptiveCompression(
threshold=2 ** 16 + 1, less=Float16Compression(), greater_equal=Uniform8BitQuantization()
)
trainer = Trainer(
strategy=HivemindStrategy(
target_batch_size=target_batch_size,
grad_compression=compression,
state_averaging_compression=compression,
),
accelerator="gpu",
devices=1,
)
PowerSGD
""""""""

`PowerSGD <https://arxiv.org/abs/1905.13727>`_ is a technique to reduce distributed communication of gradients across processes.
In short, PowerSGD uses a low-rank approximation to compress gradients before running an `all-reduce` step to sync gradients across all processes.

.. note::
Though PowerSGD can impact convergence, it can also substantially reduce communication between processes.

.. code-block:: python
from pytorch_lightning import Trainer
from lightning_hivemind.strategy import HivemindStrategy
from functools import partial
from hivemind.optim.power_sgd_averager import PowerSGDGradientAverager
trainer = Trainer(
strategy=HivemindStrategy(
target_batch_size=8192,
grad_averager_factory=partial(PowerSGDGradientAverager, averager_rank=32, min_compression_ratio=0.5),
),
accelerator="gpu",
devices=1,
)
15 changes: 15 additions & 0 deletions docs/_sources/index.rst.txt
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.. Lightning-AI-Sandbox documentation master file, created by
sphinx-quickstart on Wed Mar 25 21:34:07 2020.
You can adapt this file completely to your liking, but it should at least
contain the root `toctree` directive.
.. include:: readme.rst


.. toctree::
:maxdepth: 1
:name: start
:caption: Start here

advanced
expert
62 changes: 62 additions & 0 deletions docs/_sources/overview.rst.txt
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:orphan:

################################################################
Hivemind - training on unreliable mixed GPUs across the internet
################################################################

Collaborative Training tries to solve the need for top-tier multi-GPU servers by allowing you to train across unreliable machines,
such as local machines or even preemptible cloud compute across the internet.

Under the hood, we use `Hivemind <https://github.com/learning-at-home/hivemind>`__ which provides de-centralized training across the internet.

.. warning:: This is an :ref:`experimental <versioning:Experimental API>` feature.


To use Collaborative Training, you need to first this extension.

.. code-block:: bash
pip install lightning-hivemind
This will install both the `Hivemind <https://pypi.org/project/hivemind/>`__ package as well as the ``HivemindStrategy`` for the Lightning Trainer:

Reducing Communication By Overlapping Communication
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

We can reduce the impact of communication across all machines by overlapping communication with our training iterations. In short, we enable communication to happen in the background of training.

Overlap Gradient and State Averaging
""""""""""""""""""""""""""""""""""""

When the target batch size is reached, all processes that are included in the step send gradients and model states to each other. By enabling some flags through
the strategy, communication can happen in the background. This allows training to continue (with slightly outdated weights) but provides us the means
to overlap communication with computation.

.. warning::
Enabling overlapping communication means convergence will slightly be affected.

.. note::
Enabling these flags means that you must pass in a ``scheduler_fn`` to the ``HivemindStrategy`` instead of relying on a scheduler from ``configure_optimizers``.
The optimizer is re-created by Hivemind, and as a result, the scheduler has to be re-created.

.. code-block:: python
import torch
from functools import partial
from lightning import Trainer
from lightning_hivemind.strategy import HivemindStrategy
trainer = Trainer(
strategy=HivemindStrategy(
target_batch_size=8192,
delay_state_averaging=True,
delay_grad_averaging=True,
delay_optimizer_step=True,
offload_optimizer=True, # required to delay averaging
scheduler_fn=partial(torch.optim.lr_scheduler.ExponentialLR, gamma=...),
),
accelerator="gpu",
devices=1,
)
For more information on the strategy capabilities, see the `lightning-hivemind <https://github.com/Lightning-Universe/lightning-hivemind>`__ repo.
47 changes: 47 additions & 0 deletions docs/_sources/readme.rst.txt
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Lightning + Hivemind
====================

Collaborative Training tries to solve the need for top-tier multi-GPU
servers by allowing you to train across unreliable machines, such as
local machines or even preemptible cloud computing across the internet.

Under the hood, we use
`Hivemind <https://github.com/learning-at-home/hivemind>`__, which
provides de-centralized training across the internet.

To use Collaborative Training, you need first to have this extension.

.. code:: bash
pip install -U lightning-Hivemind
The ``HivemindStrategy`` accumulates gradients from all collaborating
processes until they reach a ``target_batch_size``. By default, we use
the batch size of the first batch to determine what each local machine
batch contributes towards the ``target_batch_size``. Once the
``target_batch_size`` is reached, an optimizer step is made on all
processes.

When using ``HivemindStrategy``, note that you cannot use gradient
accumulation (``accumulate_grad_batches``). This is because Hivemind
manages accumulation internally.

.. code:: py
from lightning import Trainer
from lightning_hivemind.strategy import HivemindStrategy
trainer = Trainer(strategy=HivemindStrategy(target_batch_size=8192), accelerator="gpu", devices=1)
Followed by:

.. code:: bash
python train.py
# Other machines can connect by running the same command:
# INITIAL_PEERS=... python train.py
# or passing the peers to the strategy:"
# HivemindStrategy(initial_peers=...)"
A helper message is printed once your training begins, showing you how
to train on other machines using the same code.
26 changes: 26 additions & 0 deletions docs/_sources/versioning.rst.txt
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:orphan:

.. warning::

This file is a placeholder for the real versioning policy page in the main
documentation. It is here so we can cross link to it from the changelog.

.. _versioning:

Versioning Policy
#################

API Stability
*************

Stable API
----------

Experimental API
----------------

API Evolution
*************

Compatibility matrix
********************
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