Stage3: Use new torch grad accumulation hooks API #6773
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* This commit addresses an issue reported in: microsoft#6718 * The existing code has been using the grad_acc node hook to reduce params grads. The constructs such as param.data = replicated_tensor.data used in allgather_params(..) are compiled into param.set() causing the hook assigned to the grad_acc node not being called. * This is a known torch issue pytorch/pytorch#139742. * The above caused accuracy issues and could be temporarily solved by simply disabling the torch compile when activation checkpointing is used. * This commit provides a clean solution by replacing the hook on a grad_acc node to a hook using a new and robust hook API on a param itself: param.register_post_accumulate_grad_hook(..)
tjruwase
reviewed
Nov 21, 2024
| self._grad_acc_hooks.append(grad_acc.register_hook(reduce_partition_and_remove_grads)) | ||
| self.grad_accs.append(grad_acc) | ||
| self._grad_acc_hooks.append( | ||
| param.register_post_accumulate_grad_hook(reduce_partition_and_remove_grads)) |
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Which pytorch version introduced this API? How should we handle older versions?
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Hi @tjruwase
- This API was introduced starting pytorch v2.1.
- We can add check what version and use the older API when needed.
- However, compilation should be disabled for the older versions to avoid the accuracy issues (if activation checkpointing is enabled).
Please advice what should be the approach. Thanks.
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The constructs such as
param.data = replicated_tensor.dataused inallgather_params(..)are compiled into
param.set()causing the hook assigned to the grad_acc node not being called.param.register_post_accumulate_grad_hook(..)