Add NoOp optimizer

llmfoundry/optim/__init__.py

@@ -10,13 +10,15 @@
 
 from llmfoundry.optim.adaptive_lion import DecoupledAdaLRLion, DecoupledClipLion
 from llmfoundry.optim.lion import DecoupledLionW
+from llmfoundry.optim.no_op import NoOp
 from llmfoundry.optim.scheduler import InverseSquareRootWithWarmupScheduler
 from llmfoundry.registry import optimizers, schedulers
 
 optimizers.register('adalr_lion', func=DecoupledAdaLRLion)
 optimizers.register('clip_lion', func=DecoupledClipLion)
 optimizers.register('decoupled_lionw', func=DecoupledLionW)
 optimizers.register('decoupled_adamw', func=DecoupledAdamW)
+optimizers.register('no_op', func=NoOp)
 
 schedulers.register('constant_with_warmup', func=ConstantWithWarmupScheduler)
 schedulers.register(
@@ -33,5 +35,6 @@
     'DecoupledLionW',
     'DecoupledClipLion',
     'DecoupledAdaLRLion',
+    'NoOp',
     'InverseSquareRootWithWarmupScheduler',
 ]

llmfoundry/optim/no_op.py

@@ -0,0 +1,44 @@
+# Copyright 2024 MosaicML LLM Foundry authors
+# SPDX-License-Identifier: Apache-2.0
+
+from typing import Any, Callable, Iterable, Optional
+
+import torch
+
+
+class NoOp(torch.optim.Optimizer):
+    """Optimizer that performs no optimization steps."""
+
+    def __init__(
+        self,
+        params: Iterable[torch.Tensor],
+    ):
+        """Initialize NoOp optimizer.
+
+        Args:
+            params (Iterable[torch.Tensor]): Model parameters for the optimizer.
+        """
+        # LR schedulers expect param groups to have LR. Unused.
+        defaults = {'lr': 0.0}
+        super().__init__(params, defaults)
+
+    def __setstate__(self, state: dict[str, dict[Any, Any]]) -> None:
+        super().__setstate__(state)
+
+    def state_dict(self):
+        return super().state_dict()
+
+    @torch.no_grad()
+    def step(self, closure: Optional[Callable] = None):
+        """Perform no-op optimization step where no parameters are updated.
+
+        Args:
+            closure (Callable, optional): A closure that reevaluates the model
+                and returns the loss.
+        """
+        loss = None
+        if closure is not None:
+            with torch.enable_grad():
+                loss = closure()
+
+        return loss

tests/optim/test_no_op.py

@@ -0,0 +1,48 @@
+# Copyright 2022 MosaicML LLM Foundry authors
+# SPDX-License-Identifier: Apache-2.0
+
+import copy
+from typing import Callable
+
+import torch
+from composer.trainer import Trainer
+from torch.utils.data import DataLoader
+
+from llmfoundry.models.mpt.modeling_mpt import ComposerMPTCausalLM
+from llmfoundry.utils.builders import build_optimizer
+
+
+def test_no_op_does_nothing(
+    build_tiny_mpt: Callable[..., ComposerMPTCausalLM],
+    tiny_ft_dataloader: DataLoader,
+):
+
+    # Build MPT model
+    model = build_tiny_mpt(
+        loss_fn='torch_crossentropy',
+        attn_config={
+            'attn_impl': 'torch',
+        },
+    )
+
+    # Build NoOp optimizer
+    no_op_optim = build_optimizer(model, 'no_op', optimizer_config={})
+
+    orig_model = copy.deepcopy(model)
+
+    # build trainer
+    trainer = Trainer(
+        model=model,
+        train_dataloader=tiny_ft_dataloader,
+        max_duration=f'2ba',
+        optimizers=no_op_optim,
+    )
+    trainer.fit()
+
+    # Check that the model has not changed
+    for (
+        (orig_name, orig_param),
+        (new_name, new_param),
+    ) in zip(orig_model.named_parameters(), model.named_parameters()):
+        print(f'Checking {orig_name} and {new_name}')
+        assert torch.equal(orig_param, new_param)