Hi,
I have trouble using multiple workers with DistributedDataParallel.
- If I set
num_workers=0
+ DDP everything works. - If I set
num_workers > 0
without DDP everything works. - If I set
num_workers > 0
with DDP I have the following error:
Traceback (most recent call last):
File "train_new.py", line 170, in <module>
trainer.train()
File "/home/matte/PhD/LV-LAB/ELVIS/elvis/trainers/distributed.py", line 38, in train
mp.spawn(self._distributed_training,
File "/home/matte/anaconda3/envs/lvlab/lib/python3.8/site-packages/torch/multiprocessing/spawn.py", line 230, in spawn
return start_processes(fn, args, nprocs, join, daemon, start_method='spawn')
File "/home/matte/anaconda3/envs/lvlab/lib/python3.8/site-packages/torch/multiprocessing/spawn.py", line 188, in start_processes
while not context.join():
File "/home/matte/anaconda3/envs/lvlab/lib/python3.8/site-packages/torch/multiprocessing/spawn.py", line 150, in join
raise ProcessRaisedException(msg, error_index, failed_process.pid)
torch.multiprocessing.spawn.ProcessRaisedException:
-- Process 0 terminated with the following error:
Traceback (most recent call last):
File "/home/matte/anaconda3/envs/lvlab/lib/python3.8/site-packages/torch/multiprocessing/spawn.py", line 59, in _wrap
fn(i, *args)
File "/home/matte/PhD/LV-LAB/ELVIS/elvis/trainers/distributed.py", line 71, in _distributed_training
self.train_loop()
File "/home/matte/PhD/LV-LAB/ELVIS/elvis/trainers/base.py", line 144, in train_loop
for batch in self._trloader:
File "/home/matte/anaconda3/envs/lvlab/lib/python3.8/site-packages/torch/utils/data/dataloader.py", line 355, in __iter__
return self._get_iterator()
File "/home/matte/anaconda3/envs/lvlab/lib/python3.8/site-packages/torch/utils/data/dataloader.py", line 301, in _get_iterator
return _MultiProcessingDataLoaderIter(self)
File "/home/matte/anaconda3/envs/lvlab/lib/python3.8/site-packages/torch/utils/data/dataloader.py", line 914, in __init__
w.start()
File "/home/matte/anaconda3/envs/lvlab/lib/python3.8/multiprocessing/process.py", line 121, in start
self._popen = self._Popen(self)
File "/home/matte/anaconda3/envs/lvlab/lib/python3.8/multiprocessing/context.py", line 224, in _Popen
return _default_context.get_context().Process._Popen(process_obj)
File "/home/matte/anaconda3/envs/lvlab/lib/python3.8/multiprocessing/context.py", line 284, in _Popen
return Popen(process_obj)
File "/home/matte/anaconda3/envs/lvlab/lib/python3.8/multiprocessing/popen_spawn_posix.py", line 32, in __init__
super().__init__(process_obj)
File "/home/matte/anaconda3/envs/lvlab/lib/python3.8/multiprocessing/popen_fork.py", line 19, in __init__
self._launch(process_obj)
File "/home/matte/anaconda3/envs/lvlab/lib/python3.8/multiprocessing/popen_spawn_posix.py", line 47, in _launch
reduction.dump(process_obj, fp)
File "/home/matte/anaconda3/envs/lvlab/lib/python3.8/multiprocessing/reduction.py", line 60, in dump
ForkingPickler(file, protocol).dump(obj)
File "/home/matte/anaconda3/envs/lvlab/lib/python3.8/site-packages/torch/multiprocessing/reductions.py", line 240, in reduce_tensor
event_sync_required) = storage._share_cuda_()
RuntimeError: Attempted to send CUDA tensor received from another process; this is not currently supported. Consider cloning before sending.
I tried to debug it without success. The only thing I know is that the error is caused when I do the first iteration on the dataloader. Anyway, the code crashes before entering the mydataset.__getitem()
. Does someone of you have any idea how to understand what is going on?