mirror of https://github.com/hpcaitech/ColossalAI
131 lines
4.5 KiB
Python
131 lines
4.5 KiB
Python
import uuid
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from copy import deepcopy
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from typing import Optional
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import torch
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from torch.types import _bool, _device, _dtype
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from torch.utils._pytree import tree_flatten, tree_map
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from .._compatibility import compatibility
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from .constants import ALIAS_ATEN
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__all__ = ['MetaTensor']
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def set_data_ptr(x):
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if isinstance(x, torch.Tensor):
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if not x.data_ptr():
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data_ptr = uuid.uuid4()
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x.data_ptr = lambda: data_ptr
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@compatibility(is_backward_compatible=False)
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class MetaTensor(torch.Tensor):
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"""
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A wrapping tensor that hacks `torch.autograd` without patching more `torch.ops.aten` ops.
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`fake_device` is the device that `MetaTensor` is supposed to run on.
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"""
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_tensor: torch.Tensor
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__slots__ = ['_tensor']
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@staticmethod
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def __new__(cls, elem, fake_device=None):
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# Avoid multiple wrapping
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if isinstance(elem, MetaTensor):
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fake_device = elem.device if fake_device is None else fake_device
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elem = elem._tensor
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# The wrapping tensor (MetaTensor) shouldn't hold any
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# memory for the class in question, but it should still
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# advertise the same device as before
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r = torch.Tensor._make_wrapper_subclass(
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cls,
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elem.size(),
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strides=elem.stride(),
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storage_offset=elem.storage_offset(),
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dtype=elem.dtype,
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layout=elem.layout,
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device=fake_device if fake_device is not None else elem.device,
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requires_grad=elem.requires_grad) # deceive the frontend for aten selections
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r._tensor = elem
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# ...the real tensor is held as an element on the tensor.
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if not r._tensor.is_meta:
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r._tensor = r._tensor.to(torch.device('meta'))
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# only tensor not on `meta` should be copied to `meta`
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set_data_ptr(r._tensor)
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return r
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def __repr__(self):
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if self.grad_fn:
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return f"MetaTensor({self._tensor}, fake_device='{self.device}', grad_fn={self.grad_fn})"
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return f"MetaTensor({self._tensor}, fake_device='{self.device}')"
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@classmethod
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def __torch_dispatch__(cls, func, types, args=(), kwargs=None):
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fake_device = None
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def unwrap(x):
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nonlocal fake_device
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if isinstance(x, MetaTensor):
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fake_device = x.device
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x = x._tensor
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elif isinstance(x, torch.Tensor):
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fake_device = x.device
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x = x.to(torch.device('meta'))
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return x
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if 'device' in kwargs:
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fake_device = kwargs['device']
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kwargs['device'] = torch.device('meta')
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args = tree_map(unwrap, args)
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kwargs = tree_map(unwrap, kwargs)
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# run aten for backend=CPU but actually on backend=Meta
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out = func(*args, **kwargs)
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# here we keep the uuid of input because ALIAS_ATEN do not generate a physical copy
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# of the input
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if func in ALIAS_ATEN:
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out.data_ptr = args[0].data_ptr
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# Now, we want to continue propagating this tensor, so we rewrap Tensors in
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# our custom tensor subclass
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def wrap(x):
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if isinstance(x, torch.Tensor):
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nonlocal fake_device
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if not x.is_meta:
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x = x.to(torch.device('meta'))
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return MetaTensor(x, fake_device=fake_device) if isinstance(x, torch.Tensor) else x
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return tree_map(wrap, out)
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def to(self, *args, **kwargs) -> torch.Tensor:
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"""An extension of `torch.Tensor.to()` to MetaTensor
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Returns:
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result (MetaTensor): MetaTensor
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Usage:
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>>> tensor = MetaTensor(torch.rand(10), fake_device='cuda:100')
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>>> tensor.to(torch.uint8)
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MetaTensor(tensor(..., device='meta', size=(10,), dtype=torch.uint8), fake_device='cuda:100')
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>>> tensor.to(torch.device('cuda:42'))
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MetaTensor(tensor(..., device='meta', size=(10,)), fake_device='cuda:42')
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>>> tensor.to('vulkan')
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MetaTensor(tensor(..., device='meta', size=(10,)), fake_device='vulkan')
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"""
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# this imitates c++ function in the way of @overload
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device = None
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for arg in args:
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if isinstance(arg, str) or isinstance(arg, _device):
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device = arg
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if 'device' in kwargs:
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device = kwargs['device']
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result = super().to(*args, **kwargs)
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if device is not None:
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result = MetaTensor(result, fake_device=device)
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return result
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