MALA-DDP

docs/source/advanced_usage/trainingmodel.rst

@@ -220,3 +220,68 @@ via
 
 The full path for ``path_to_visualization`` can be accessed via
 ``trainer.full_visualization_path``.
+
+
+Training in parallel
+********************
+
+If large models or large data sets are employed, training may be slow even
+if a GPU is used. In this case, multiple GPUs can be employed with MALA
+using the ``DistributedDataParallel`` (DDP) formalism of the ``torch`` library.
+To use DDP, make sure you have `NCCL <https://developer.nvidia.com/nccl>`_
+installed on your system.
+
+To activate and use DDP in MALA, almost no modification of your training script
+is necessary. Simply activate DDP in your ``Parameters`` object. Make sure to
+also enable GPU, since parallel training is currently only supported on GPUs.
+
+      .. code-block:: python
+
+            parameters = mala.Parameters()
+            parameters.use_gpu = True
+            parameters.use_ddp = True
+
+MALA is now set up for parallel training. DDP works across multiple compute
+nodes on HPC infrastructure as well as on a single machine hosting multiple
+GPUs. While essentially no modification of the python script is necessary, some
+modifications for calling the python script may be necessary, to ensure
+that DDP has all the information it needs for inter/intra-node communication.
+This setup *may* differ across machines/clusters. During testing, the
+following setup was confirmed to work on an HPC cluster using the
+``slurm`` scheduler.
+
+    .. code-block:: bash
+
+        #SBATCH --nodes=NUMBER_OF_NODES
+        #SBATCH --ntasks-per-node=NUMBER_OF_TASKS_PER_NODE
+        #SBATCH --gres=gpu:NUMBER_OF_TASKS_PER_NODE
+        # Add more arguments as needed
+        ...
+
+        # Load more modules as needed
+        ...
+
+        # This port can be arbitrarily chosen.
+        # Given here is the torchrun default
+        export MASTER_PORT=29500
+
+        # Find out the host node.
+        echo "NODELIST="${SLURM_NODELIST}
+        master_addr=$(scontrol show hostnames "$SLURM_JOB_NODELIST" | head -n 1)
+        export MASTER_ADDR=$master_addr
+        echo "MASTER_ADDR="$MASTER_ADDR
+
+        # Run using srun.
+        srun -u bash -c '
+        # Export additional per process variables
+        export RANK=$SLURM_PROCID
+        export LOCAL_RANK=$SLURM_LOCALID
+        export WORLD_SIZE=$SLURM_NTASKS
+
+        python3 -u  training.py
+        '
+
+An overview of environment variables to be set can be found `in the official documentation <https://pytorch.org/docs/stable/distributed.html#environment-variable-initialization>`_.
+A general tutorial on DDP itself can be found `here <https://pytorch.org/tutorials/beginner/ddp_series_theory.html>`_.
+
+

install/mala_gpu_base_environment.yml

@@ -1,4 +1,6 @@
 name: mala-gpu
 channels:
-  - defaults
   - conda-forge
+  - defaults
+dependencies:
+  - python=3.10

mala/common/check_modules.py

@@ -11,10 +11,6 @@ def check_modules():
             "available": False,
             "description": "Enables inference parallelization.",
         },
-        "horovod": {
-            "available": False,
-            "description": "Enables training parallelization.",
-        },
         "lammps": {
             "available": False,
             "description": "Enables descriptor calculation for data preprocessing "

mala/common/parallelizer.py

@@ -2,15 +2,13 @@
 
 from collections import defaultdict
 import platform
+import os
 import warnings
 
-try:
-    import horovod.torch as hvd
-except ModuleNotFoundError:
-    pass
 import torch
+import torch.distributed as dist
 
-use_horovod = False
+use_ddp = False
 use_mpi = False
 comm = None
 local_mpi_rank = None
@@ -33,45 +31,43 @@ def set_current_verbosity(new_value):
     current_verbosity = new_value
 
 
-def set_horovod_status(new_value):
+def set_ddp_status(new_value):
     """
-    Set the horovod status.
+    Set the ddp status.
 
-    By setting the horovod status via this function it can be ensured that
+    By setting the ddp status via this function it can be ensured that
     printing works in parallel. The Parameters class does that for the user.
 
     Parameters
     ----------
     new_value : bool
-        Value the horovod status has.
+        Value the ddp status has.
 
     """
     if use_mpi is True and new_value is True:
         raise Exception(
-            "Cannot use horovod and inference-level MPI at "
-            "the same time yet."
+            "Cannot use ddp and inference-level MPI at " "the same time yet."
         )
-    global use_horovod
-    use_horovod = new_value
+    global use_ddp
+    use_ddp = new_value
 
 
 def set_mpi_status(new_value):
     """
     Set the MPI status.
 
-    By setting the horovod status via this function it can be ensured that
+    By setting the MPI status via this function it can be ensured that
     printing works in parallel. The Parameters class does that for the user.
 
     Parameters
     ----------
     new_value : bool
-        Value the horovod status has.
+        Value the MPI status has.
 
     """
-    if use_horovod is True and new_value is True:
+    if use_ddp is True and new_value is True:
         raise Exception(
-            "Cannot use horovod and inference-level MPI at "
-            "the same time yet."
+            "Cannot use ddp and inference-level MPI at " "the same time yet."
         )
     global use_mpi
     use_mpi = new_value
@@ -119,8 +115,8 @@ def get_rank():
         The rank of the current thread.
 
     """
-    if use_horovod:
-        return hvd.rank()
+    if use_ddp:
+        return dist.get_rank()
     if use_mpi:
         return comm.Get_rank()
     return 0
@@ -159,8 +155,8 @@ def get_local_rank():
     FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER
     DEALINGS IN THE SOFTWARE.
     """
-    if use_horovod:
-        return hvd.local_rank()
+    if use_ddp:
+        return int(os.environ.get("LOCAL_RANK"))
     if use_mpi:
         global local_mpi_rank
         if local_mpi_rank is None:
@@ -187,8 +183,8 @@ def get_size():
     size : int
         The number of ranks.
     """
-    if use_horovod:
-        return hvd.size()
+    if use_ddp:
+        return dist.get_world_size()
     if use_mpi:
         return comm.Get_size()
 
@@ -209,8 +205,8 @@ def get_comm():
 
 def barrier():
     """General interface for a barrier."""
-    if use_horovod:
-        hvd.allreduce(torch.tensor(0), name="barrier")
+    if use_ddp:
+        dist.barrier()
     if use_mpi:
         comm.Barrier()
     return