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Make StaticCache configurable at model construct time
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Guang Yang
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Sep 3, 2024
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from packaging import version | ||
|
||
from transformers.testing_utils import ( | ||
is_torch_available, | ||
require_torch, | ||
) | ||
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if is_torch_available(): | ||
import torch | ||
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from transformers import ( | ||
PreTrainedModel, | ||
StaticCache, | ||
) | ||
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@require_torch | ||
class TorchExportatibleModuleWithStaticCache(torch.nn.Module): | ||
""" | ||
A wrapper module designed to make a `PreTrainedModel` exportable with `torch.export`, | ||
specifically for use with static caching. This module ensures that the exported model | ||
is compatible with further lowering and execution in `ExecuTorch`. | ||
Args: | ||
model (PreTrainedModel): The pretrained model to wrap. The model must have caching | ||
enabled and use a 'static' caching implementation. | ||
Attributes: | ||
model (PreTrainedModel): The underlying pretrained model. | ||
static_cache (StaticCache): A static cache instance used to store past key values for faster inference. | ||
is_causal (bool): Indicates whether the model architecture supports causal masking (e.g., causal language models). | ||
Note: | ||
This class is specifically designed to support export process using `torch.export` | ||
in a way that ensures the model can be further lowered and run efficiently in `ExecuTorch`. | ||
Raises: | ||
AssertionError: If `model` does not have caching enabled or if it does not use a 'static' caching implementation. | ||
""" | ||
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def __init__(self, model: PreTrainedModel): | ||
super().__init__() | ||
assert model.generation_config.use_cache is True | ||
assert model.generation_config.cache_implementation == "static" | ||
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self.model = model | ||
self.static_cache = StaticCache( | ||
config=self.model.config, | ||
batch_size=self.model.generation_config.cache_config.batch_size, | ||
max_cache_len=self.model.generation_config.cache_config.max_cache_len, | ||
dtype=self.model.config.torch_dtype, | ||
) | ||
self.is_causal = any("CausalLM" in arch for arch in self.model.config.architectures) | ||
if self.is_causal: | ||
causal_mask = torch.tril( | ||
torch.ones( | ||
self.static_cache.max_cache_len, | ||
self.static_cache.max_cache_len, | ||
dtype=torch.bool, | ||
) | ||
) | ||
self.register_buffer("mask", causal_mask, persistent=False) | ||
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def forward(self, input_ids: torch.Tensor, cache_position: torch.Tensor): | ||
""" | ||
Forward pass of the module, which is compatible with the ExecuTorch runtime. | ||
Args: | ||
input_ids (torch.Tensor): Tensor representing current input token id to the module. | ||
cache_position (torch.Tensor): Tensor representing current input position in the cache. | ||
Returns: | ||
torch.Tensor: Logits output from the model. | ||
This forward adapter serves two primary purposes: | ||
1. **Making the Model `torch.export`-Compatible**: | ||
The adapter hides unsupported objects, such as the `Cache`, from the graph inputs and outputs, | ||
enabling the model to be exportable using `torch.export` without encountering issues. | ||
2. **Ensuring Compatibility with `ExecuTorch` runtime**: | ||
The adapter matches the model's forward signature with that in `executorch/extension/llm/runner`, | ||
ensuring that the exported model can be executed in `ExecuTorch` out-of-the-box. | ||
""" | ||
_, seqlen = input_ids.shape | ||
attn_mask = self.mask[cache_position, :seqlen] if self.is_causal else None | ||
outs = self.model( | ||
input_ids=input_ids, | ||
attention_mask=attn_mask, | ||
position_ids=cache_position.unsqueeze(0), | ||
cache_position=cache_position, | ||
past_key_values=self.static_cache, | ||
use_cache=True, | ||
) | ||
return outs.logits | ||
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@require_torch | ||
def convert_and_export( | ||
model: PreTrainedModel, | ||
example_input_ids: torch.Tensor = None, | ||
example_cache_position: torch.Tensor = None, | ||
): | ||
""" | ||
Convert a `PreTrainedModel` into an exportable module and export it using `torch.export`, | ||
ensuring the exported model is compatible with `ExecuTorch`. | ||
Args: | ||
model (PreTrainedModel): The pretrained model to be exported. | ||
example_input_ids (torch.Tensor): Example input token id used by `torch.export`. | ||
example_cache_position (torch.Tensor): Example current cache position used by `torch.export`. | ||
Returns: | ||
torch.export.ExportedProgram: The exported program generated via `torch.export`. | ||
""" | ||
import torch | ||
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assert version.parse(torch.__version__) >= version.parse("2.3"), "VersionError: torch >= 2.3 is required." | ||
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with torch.no_grad(): | ||
# Due to issue https://github.com/pytorch/pytorch/issues/128394, we need to switch to use an internal | ||
# export API and pre_dispatch=False. Switch to use the public API once the issue is included in 2.5 release. | ||
import torch.export._trace | ||
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example_input_ids = ( | ||
example_input_ids if example_input_ids is not None else torch.tensor([[1]], dtype=torch.long) | ||
) | ||
example_cache_position = ( | ||
example_cache_position if example_cache_position is not None else torch.tensor([0], dtype=torch.long) | ||
) | ||
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exported_program = torch.export._trace._export( | ||
TorchExportatibleModuleWithStaticCache(model), | ||
args=(example_input_ids,), | ||
kwargs={"cache_position": example_cache_position}, | ||
pre_dispatch=False, | ||
strict=True, | ||
) | ||
return exported_program |
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