Releases: horovod/horovod
Process sets, XLA support, improved GPU backend
Added
-
Added process sets to concurrently run collective operations on subsets of Horovod processes in TensorFlow, PyTorch, and MXNet. (#2839, #3042, #3043, #3054, #3083, #3090)
-
Added XLA support for Allreduce via
tf.function(jit_compile=True)
. (#3053) -
Added fused buffer scaling and unpack/pack kernels on GPU. (#2973)
-
Added support for NCCL on CUDA 11.4. (#3182)
-
Added fp16 compression for MXNet. (#2987)
-
Added terminate_on_nan flag to Spark Lightning estimator. (#3088)
-
Added barrier() API to torch module to support simple synchronization among ranks and to achieve parity with PyTorch DDP and similar frameworks. #3139
-
Added params for customizing Tensorboard callback. (#3153)
-
Added
hvd.cross_rank()
for keras. (#3008) -
Added barrier() API to torch module to support simple synchronization among ranks and to achieve parity with PyTorch DDP and similar frameworks. #3139
Changed
-
Implemented more asynchronous dependency handling on GPU. (#2963)
-
Ray: RayExecutor will now use the current placement group instead of always creating a new one. (#3134)
-
Lightning: turned off shuffling for validation dataset. (#2974)
-
Ray: RayExecutor will use the current placement group if one exists. (#3134)
-
Extended
hvd.join()
to return the last rank that joined. (#3097)
Removed
- Spark/Keras: remove bare Keras support. (#3191)
Fixed
-
Fix Horovod develop/editable install mode and incremental builds. (#3074)
-
Estimator/Lightning: use lightning datamodule. (#3084)
-
Fix Horovod Spark StringType and numpy type mapping issue. (#3146)
-
Fixed error in Keras LearningRateScheduler. (#3135)
-
Fixed bug in Lightning Profiler on Ray. (#3122)
-
Fixed torch op lazy release to prevent OOM in elastic training. (#3110)
-
Lightning: Fixed usage of the checkpoint callback. (#3186)
-
Fixed MPICH support to use Intel MPI's implementation. (#3148)
-
Fixed race condition in PyTorch async dataloader. (#3120)
Remote filesystem support, estimator fixes
Added
-
Estimator: added support for loading data from S3, GCS, ADLS, and other remote filesystems. (#2927)
-
Estimator: added custom Spark data loader interface. (#2938)
-
LightningEstimator: added support to supply a logger and associated parameter to control the frequency of logging. (#2926)
-
Estimator: added check to ensure all ranks have the same device type. (#2942)
Changed
-
Changed behavior from using TensorBoardLogger to now using it as a fallback if a logger is not supplied. (#2926)
-
Ray: disabled capturing child tasks in placement group. (#2920)
Fixed
PyTorch Lightning Estimator, Nsight profiling, PyTorch 1.9 support
Added
-
Added pytorch_lightning spark estimator which enables training pytorch_lightning models. (#2713)
-
Added NVTX tracing hooks for profiling with Nsight Systems. (#2723)
-
Added a generic
num_workers
API forRayExecutor
(#2870) -
Supports Ray Client without code changes. (#2882)
-
Supports inmemory cache option for Keras Estimator. (#2896)
-
Added FP16 support for GPU tensor in mxnet. (#2915)
-
Added response caching for allgather operations. (#2872)
-
Estimator: add petastorm reader_pool_type into constructor (#2903)
Changed
-
Changed
alltoall
to return the received splits as a second return value if non-uniform splits are sent. (#2631) -
Changed
RayExecutor
to use Ray Placement Groups for worker colocation. (#2824) -
Changed
Inmemory dataloader
usage for Torch Estimator with petastorm v0.11.0 release. (#2896)
Fixed
Local Gradient Aggregation, Grouped Allreduce
Detailed Changes
Added
-
Added support for backward_passes_per_step > 1 for TF Keras graph mode. (#2346)
-
Added support for backward_passes_per_step > 1 for TF Keras eager execution. (#2371)
-
Added support for backward_passes_per_step > 1 for TF LegacyOptimizer in graph mode. (#2401)
-
Added grouped allreduce to enable more efficient tensor fusion and deterministic training. (#2453)
-
Add support for specifying
op
andcompression
inhorovod.tensorflow.keras.allreduce()
. (#2423) -
Adding support for batched D2D memcopy kernel on GPU. (#2435)
-
Added schema inference in Spark Estimator without sampling. (#2373)
-
Added
Store.create("dbfs:/")
mapping toDBFSLocalStore("/dbfs/...")
. (#2376)
Changed
-
Changed Keras callbacks to require parameter
initial_lr
ofLearningRateScheduleCallback
andLearningRateWarmupCallback
. (#2459) -
Changed default cycle time from 5ms to 1ms and fusion threshold from 64MB to 128MB. (#2468)
Fixed
-
Fixed support for TensorFlow v2.4.0. (#2381)
-
Fixed averaging using CUDA half2 implementation one element half buffers. (#2375)
-
Fixed
HOROVOD_THREAD_AFFINITY
when using oneCCL. (#2350) -
Added timeout to SSH check in horovodrun to prevent hanging. (#2448)
-
Added
HOROVOD_GLOO_TIMEOUT_SECONDS
value to error messages. (#2436) -
Fixed race condition in dynamic timeline API. (#2341)
-
Fixed --log-hide-timestamp to apply to driver logs with Gloo. (#2388)
Elastic Horovod on Ray
Hotfix: build without MXNet installed
Detailed Changes
Fixed
- Fixed building Horovod without HOROVOD_WITHOUT_MXNET when MXNet is not installed. (#2334)
Bugfixes, Databricks Runtime support for Estimators, ElasticSampler
Detailed Changes
Added
-
Added Databricks storage
DBFSLocalStore
and support for GPU-aware scheduling to horovod.spark Estimator. (#2234) -
Added ElasticSampler and PyTorch Elastic ImageNet example. (#2297)
-
Added ability to dynamically start and stop timeline programmatically. (#2215)
-
Added support for Gloo on macOS. (#2254)
-
Exposed name argument to TensorFlow allreduce operation. (#2325)
-
Added option to strip outer name scope from Horovod ops in TensorFlow. (#2328)
Fixed
-
Fixed usage of VERBOSE=1 when setting custom MAKEFLAGS. (#2239)
-
Fixed bugs in Keras Elastic Callback classes. (#2289)
-
Fixed RelWithDebInfo build and made it the default with -03 optimizations. (#2305)
-
Fixed usage of tf.cond in TensorFlow alltoall gradient. (#2327)
-
Fixed allreduce averaging for TF IndexedSlices in ROCm path. (#2279)
-
Include stdexcept to handle certain compiler / frameworks that don't include it already. (#2238)
-
Fixed Debug builds by setting compiler options based on CMake build type. (#2263)
-
Skipped launching zero-sized send/recvs for NCCLAlltoall. (#2273)
-
Fixed missing run in tf keras elastic mode. (#2272)
-
Fixed loss function in TensorFlow2 elastic synthetic benchmark. (#2265)
-
Fixed usage of HOROVOD_MIXED_INSTALL env var in alltoall tests. (#2266)
-
Removed keras requirement from Ray example. (#2262)
Elastic Horovod, Ray integration, All-to-All, Gradient Predivide, CMake build system
Elastic Horovod API + Spark Auto-Scaling (#1849, #1956)
Elastic training enables Horovod to scale up and down the number of workers dynamically at runtime, without requiring a restart or resuming from checkpoints saved to durable storage. With elastic training, workers can come and go from the Horovod job without interrupting the training process.
Support for auto-scaling can be added to any existing Horovod script with just a few modifications:
- Decorate retryable functions with
@hvd.elastic.run
. - Track state that needs to be kept in sync across workers in a
hvd.elastic.State
object. - Perform all Horovod collective operations (allreduce, allgather, broadcast, etc.) inside the retryable functions.
Here's an example for PyTorch:
import torch
import horovod.torch as hvd
hvd.init()
torch.cuda.set_device(hvd.local_rank())
model = ...
dataset = ...
@hvd.elastic.run
def train(state):
for state.epoch in range(state.epoch, args.epochs + 1):
dataset.set_epoch(state.epoch)
dataset.set_batch_idx(state.batch_idx)
for state.batch_idx, (data, target) in enumerate(dataset):
state.optimizer.zero_grad()
output = state.model(data)
loss = F.nll_loss(output, target)
loss.backward()
state.optimizer.step()
state.commit()
optimizer = optim.SGD(model.parameters(), lr * hvd.size())
optimizer = hvd.DistributedOptimizer(optimizer)
def on_state_reset():
# adjust learning rate on reset
for param_group in optimizer.param_groups:
param_group['lr'] = lr * hvd.size()
state = hvd.elastic.TorchState(model, optimizer, epoch=1, batch_idx=0)
state.register_reset_callbacks([on_state_reset])
train(state)
Run using horovodrun
by specifying the minimum and maximum number of worker processes, as well as a "host discovery script" that will be used to find available workers to add at runtime:
$ horovodrun -np 8 --min-np 4 --max-np 12 --host-discovery-script discover_hosts.sh python train.py
Elastic Horovod is supported natively with Spark auto-scaling using the hvd.spark.run_elastic
API.
For more details, see Elastic Horovod.
Horovod on Ray (#2218)
Ray is a distributed execution framework that makes it easy to provision and scale distributed applications, and can now be used to execute Horovod jobs without needing to coordinate the workers by hand:
from horovod.ray import RayExecutor
# Start the Ray cluster or attach to an existing Ray cluster
ray.init()
# Start num_hosts * num_slots actors on the cluster
executor = RayExecutor(
setting, num_hosts=num_hosts, num_slots=num_slots, use_gpu=True)
# Launch the Ray actors on each machine
# This will launch `num_slots` actors on each machine
executor.start()
# Using the stateless `run` method, a function can take in any args or kwargs
def train_fn():
hvd.init()
# Train the model on each worker here
...
# Execute the function on all workers at once
results = executor.run(train_fn)
executor.shutdown()
Horovod now also integrates with Ray Tune to scale up your hyperparameter search jobs. Check out the example here.
For more details, see Horovod on Ray.
All-to-All Operation (#2143)
The all-to-all collective can be described as a combination of a scatter and gather, where each worker will scatter a tensor to each worker, while also gathering scattered data from other workers. This type of collective communication can arise in model-parallel training strategies.
The hvd.alltoall
function takes the form hvd.alltoall(tensor, splits=None)
,
where tensor
is a multi-dimensional tensor of data to scattered and splits
is an optional 1D tensor of integers with length equal to the number of workers, describing how to split and distribute tensor. splits
is applied along the first dimension of tensor
. If splits is not provided, an equal splitting is assumed, where the first dimension is divided by the number of workers.
The implementation supports TensorFlow, PyTorch, and MXNet using the MPI backend, the CUDA-aware MPI backend via HOROVOD_GPU_ALLTOALL=MPI
, and the NCCL backend via HOROVOD_GPU_ALLTOALL=NCCL
/ HOROVOD_GPU_OPERATIONS=NCCL
.
Gradient Predivide Factor (#1949)
We've added a gradient_predivide_factor
parameter in the DistributedOptimizer
, the purpose of which is to enable splitting the averaging before and after the allreduce. This can be useful in managing the numerical range for mixed precision computations.
The gradient_predivide_factor
is applied as follows:
If op == Average, gradient_predivide_factor splits the averaging
before and after the sum. Gradients are scaled by
1.0 / gradient_predivide_factor before the sum and
gradient_predivide_factor / size after the sum.
To facilitate this, additional arguments (prescale_factor
and postscale_factor
) have been added to the basic hvd.allreduce
functions, enabling the definition of multiplicative factors to scale the tensors before and after the allreduce respectively. For efficiency, the pre and post-scaling is implemented in the Horovod backend on the fused tensor buffer, rather than through framework level operations. For GPU, this required a CUDA kernel implementation to scale the GPU buffer which in turn, required adding compilation of CUDA code to the current build infrastructure.
As an additional general benefit from these changes, gradient averaging in the optimizer can now be carried out within the Horovod backend on the fused tensor buffer using the postscale_factor
argument, rather than on a tensor by tensor basis at the framework level, decreasing the overhead of each allreduce call.
CMake Build System (#2009)
CMake, previously used to compile the optional Gloo controller, is now required to install Horovod. This change introduces a number of exciting benefits for Horovod developers and users:
- Much faster installation times through a parallel task build
- Incremental builds (almost instantaneous build when developing and making small changes at a time)
- Separation of the build config phase with the build phase (less overhead for repeated builds)
- Reuse
find_package
modules provided by CMake for MPI, CUDA, etc. to better handle a range of environment configurations - Libraries can be built outside of the python build process (no longer requiring
setup.py
) - Flexibility for the build system (make, ninja, IDEs, etc.)
Detailed Changes
Added
-
Added bare-metal elastic mode implementation to enable auto-scaling and fault tolerance. (#1849)
-
Added Elastic Horovod support for Spark auto-scaling. (#1956)
-
Added All-to-All operation for TensorFlow, PyTorch, and MXNet. (#2143)
-
Added support for
gradient_predivide_factor
and averaging in Horovod backend. (#1949) -
Added NCCL implementation of the allgather operation. (#1952)
-
Added
HOROVOD_GPU_OPERATIONS
installation variable to simplify enabling NCCL support for all GPU operations. (#1960) -
Added TensorFlow implementation of
SyncBatchNormalization
layer. (#2075) -
Added
hvd.is_initialized()
method. (#2020) -
Added
hvd.allgather_object
function for TensorFlow, PyTorch, and MXNet. (#2166) -
Added
hvd.broadcast_object
function for MXNet. (#2122) -
Added
label_shapes
parameter to KerasEstimator and TorchEstimator. (#2140) -
Added optional
modelCheckPoint
callback to KerasEstimator params. (#2124) -
Added
ssh_identity_file
argument tohorovodrun
. (#2201) -
Added support for
horovodrun
onkubeflow/mpi-job
. (#2199) -
Added Ray integration. (#2218)
Changed
-
Moved
horovod.run.runner.run
tohorovod.run
. (#2099) -
HOROVOD_THREAD_AFFINITY accepts multiple values, one for every Horovod rank (#2131)
-
Migrated build system for native libraries to CMake (#2009)
Deprecated
- HOROVOD_CCL_BGT_AFFINITY is deprected. Use HOROVOD_THREAD_AFFINITY instead (#2131)
Removed
Hotfix for adding PYTHONPATH to mpirun env
Fixed
- Added PYTHONPATH to mpirun env. (#2038)