Initialize distributed using multiproc with all visible GPUs

Summary: Pull Request resolved: facebookresearch#695

Differential Revision: D15182613

Pulled By: myleott

fbshipit-source-id: 4196346517d8e75ed9e903e9e01ab943d086f6f1

Author: Myle Ott

fairseq/distributed_utils.py

@@ -8,6 +8,7 @@
 from collections import namedtuple
 import os
 import pickle
+import socket
 import subprocess
 import warnings
 
@@ -42,9 +43,20 @@ def infer_init_method(args):
                 hostnames = subprocess.check_output(['scontrol', 'show', 'hostnames', node_list])
                 args.distributed_init_method = 'tcp://{host}:{port}'.format(
                     host=hostnames.split()[0].decode('utf-8'),
-                    port=args.distributed_port)
-                args.distributed_rank = int(os.environ.get('SLURM_PROCID'))
-                args.device_id = int(os.environ.get('SLURM_LOCALID'))
+                    port=args.distributed_port,
+                )
+                nnodes = int(os.environ.get('SLURM_NNODES'))
+                ntasks_per_node = int(os.environ.get('SLURM_NTASKS_PER_NODE'))
+                if ntasks_per_node == 1:
+                    assert args.distributed_world_size % nnodes == 0
+                    gpus_per_node = args.distributed_world_size // nnodes
+                    node_id = int(os.environ.get('SLURM_NODEID'))
+                    args.distributed_rank = node_id * gpus_per_node
+                else:
+                    assert ntasks_per_node == args.distributed_world_size // nnodes
+                    args.distributed_no_spawn = True
+                    args.distributed_rank = int(os.environ.get('SLURM_PROCID'))
+                    args.device_id = int(os.environ.get('SLURM_LOCALID'))
             except subprocess.CalledProcessError as e:  # scontrol failed
                 raise e
             except FileNotFoundError:  # Slurm is not installed
@@ -60,13 +72,17 @@ def distributed_init(args):
     else:
         print('| distributed init (rank {}): {}'.format(
             args.distributed_rank, args.distributed_init_method), flush=True)
-
         dist.init_process_group(
             backend=args.distributed_backend,
             init_method=args.distributed_init_method,
             world_size=args.distributed_world_size,
             rank=args.distributed_rank,
         )
+        print('| initialized host {} as rank {}'.format(
+            socket.gethostname(), args.distributed_rank), flush=True)
+
+        # perform a dummy all-reduce to initialize the NCCL communicator
+        dist.all_reduce(torch.rand(1).cuda())
 
         suppress_output(is_master(args))
 

fairseq/options.py

@@ -266,6 +266,8 @@ def add_distributed_training_args(parser):
                        help='port number (not required if using --distributed-init-method)')
     group.add_argument('--device-id', '--local_rank', default=0, type=int,
                        help='which GPU to use (usually configured automatically)')
+    group.add_argument('--distributed-no-spawn', action='store_true',
+                       help='do not spawn multiple processes even if multiple GPUs are visible')
     group.add_argument('--ddp-backend', default='c10d', type=str,
                        choices=['c10d', 'no_c10d'],
                        help='DistributedDataParallel backend')

train.py

@@ -23,16 +23,21 @@
 from fairseq.meters import AverageMeter, StopwatchMeter
 
 
-def main(args):
+def main(args, init_distributed=False):
     utils.import_user_module(args)
 
-    if args.max_tokens is None:
-        args.max_tokens = 6000
-    print(args)
+    assert args.max_tokens is not None or args.max_sentences is not None, \
+        'Must specify batch size either with --max-tokens or --max-sentences'
 
+    # Initialize CUDA and distributed training
     if torch.cuda.is_available() and not args.cpu:
         torch.cuda.set_device(args.device_id)
     torch.manual_seed(args.seed)
+    if init_distributed:
+        args.distributed_rank = distributed_utils.distributed_init(args)
+
+    # Print args
+    print(args)
 
     # Setup task, e.g., translation, language modeling, etc.
     task = tasks.setup_task(args)
@@ -372,11 +377,11 @@ def load_dataset_splits(args, task):
                 raise e
 
 
-def distributed_main(i, args):
+def distributed_main(i, args, start_rank=0):
     args.device_id = i
     if args.distributed_rank is None:  # torch.multiprocessing.spawn
-        args.distributed_rank = i
-    main(args)
+        args.distributed_rank = start_rank + i
+    main(args, init_distributed=True)
 
 
 def cli_main():
@@ -388,9 +393,19 @@ def cli_main():
 
     if args.distributed_init_method is not None:
         # distributed training
-        distributed_main(args.device_id, args)
+        if torch.cuda.device_count() > 1 and not args.distributed_no_spawn:
+            start_rank = args.distributed_rank
+            args.distributed_rank = None  # assign automatically
+            torch.multiprocessing.spawn(
+                fn=distributed_main,
+                args=(args, start_rank),
+                nprocs=torch.cuda.device_count(),
+            )
+        else:
+            distributed_main(args.device_id, args)
     elif args.distributed_world_size > 1:
         # fallback for single node with multiple GPUs
+        assert args.distributed_world_size <= torch.cuda.device_count()
         port = random.randint(10000, 20000)
         args.distributed_init_method = 'tcp://localhost:{port}'.format(port=port)
         args.distributed_rank = None  # set based on device id