`allreduce_gradients` breaks in the `narrow` operation

[tchaton]

Dear people from DeepSpeed,

Associated PR: https://github.com/PyTorchLightning/pytorch-lightning/pull/6546/files

Here is the associated tests causing this error message:
https://github.com/PyTorchLightning/pytorch-lightning/blob/d273393ece9c207b02f02c38e3eb8ddb71b32605/tests/plugins/test_deepspeed_plugin.py#L413

Traceback (most recent call last):
  File "/home/ubuntu/pytorch-lightning/pytorch_lightning/trainer/trainer.py", line 589, in run_train
    self.train_loop.run_training_epoch()
  File "/home/ubuntu/pytorch-lightning/pytorch_lightning/trainer/training_loop.py", line 491, in run_training_epoch
    batch_output = self.run_training_batch(batch, batch_idx, dataloader_idx)
  File "/home/ubuntu/pytorch-lightning/pytorch_lightning/trainer/training_loop.py", line 650, in run_training_batch
    self.optimizer_step(optimizer, opt_idx, batch_idx, train_step_and_backward_closure)
  File "/home/ubuntu/pytorch-lightning/pytorch_lightning/trainer/training_loop.py", line 425, in optimizer_step
    model_ref.optimizer_step(
  File "/home/ubuntu/pytorch-lightning/pytorch_lightning/core/lightning.py", line 1397, in optimizer_step
    optimizer.step(closure=optimizer_closure)
  File "/home/ubuntu/pytorch-lightning/pytorch_lightning/core/optimizer.py", line 214, in step
    self.__optimizer_step(*args, closure=closure, profiler_name=profiler_name, **kwargs)
  File "/home/ubuntu/pytorch-lightning/pytorch_lightning/core/optimizer.py", line 134, in __optimizer_step
    trainer.accelerator.optimizer_step(optimizer, self._optimizer_idx, lambda_closure=closure, **kwargs)
  File "/home/ubuntu/pytorch-lightning/pytorch_lightning/accelerators/accelerator.py", line 285, in optimizer_step
    make_optimizer_step = self.precision_plugin.pre_optimizer_step(
  File "/home/ubuntu/pytorch-lightning/pytorch_lightning/plugins/precision/deepspeed_precision.py", line 46, in pre_optimizer_step
    lambda_closure()
  File "/home/ubuntu/pytorch-lightning/pytorch_lightning/trainer/training_loop.py", line 644, in train_step_and_backward_closure
    result = self.training_step_and_backward(
  File "/home/ubuntu/pytorch-lightning/pytorch_lightning/trainer/training_loop.py", line 751, in training_step_and_backward
    self.backward(result, optimizer, opt_idx)
  File "/home/ubuntu/pytorch-lightning/pytorch_lightning/trainer/training_loop.py", line 780, in backward
    result.closure_loss = self.trainer.accelerator.backward(
  File "/home/ubuntu/pytorch-lightning/pytorch_lightning/accelerators/accelerator.py", line 268, in backward
    output = self.precision_plugin.backward(
  File "/home/ubuntu/pytorch-lightning/pytorch_lightning/plugins/precision/deepspeed_precision.py", line 72, in backward
    deepspeed_engine.backward(closure_loss, *args, **kwargs)
  File "/opt/conda/lib/python3.8/site-packages/deepspeed/runtime/engine.py", line 1004, in backward
    self.allreduce_gradients()
  File "/opt/conda/lib/python3.8/site-packages/deepspeed/runtime/engine.py", line 924, in allreduce_gradients
    self.optimizer.overlapping_partition_gradients_reduce_epilogue()
  File "/opt/conda/lib/python3.8/site-packages/deepspeed/runtime/zero/stage3.py", line 1378, in overlapping_partition_gradients_reduce_epilogue
    self.independent_gradient_partition_epilogue()
  File "/opt/conda/lib/python3.8/site-packages/deepspeed/runtime/zero/stage3.py", line 1291, in independent_gradient_partition_epilogue
    self.averaged_gradients[i] = [
  File "/opt/conda/lib/python3.8/site-packages/deepspeed/runtime/zero/stage3.py", line 1293, in <listcomp>
    param.grad.data.narrow(0,
RuntimeError: start (0) + length (2) exceeds dimension size (1).

Any ideas on how to solve this ?

Best,
T.C

[samyam]

@tchaton This bug should have been fixed by this PR. Can you please do a fresh pull and try again? Also DeepSpeed 0.3.13 is live on PyPI now which contains the fix.

[tchaton]

Hey @samyam,

I confirm the fix worked !

Best,
T.C