Enable QuickGelu Function for CLIP models (#1408)

* enabling quick_gelu fn

* better docformat

* test for act_fn

* fix comments

* changes for pre-commit

llmfoundry/models/layers/ffn.py

@@ -53,6 +53,19 @@
 }
 
 
+def quickgelu_activation(input: torch.Tensor) -> torch.Tensor:
+    """Applies GELU approximation that is fast but somewhat inaccurate.
+
+    Args:
+        input (torch.Tensor): Input tensor of shape(*), where * means any
+            number of dimensions
+
+    Returns:
+        torch.Tensor: Tensor with same shape as input tensor
+    """
+    return input * torch.sigmoid(1.702 * input)
+
+
 def resolve_ffn_act_fn(
     config: Optional[dict] = None,
 ) -> Callable[[torch.Tensor], torch.Tensor]:
@@ -70,10 +83,13 @@ def resolve_ffn_act_fn(
         config = _FFN_ACT_FN_DEFAULT
     config = deepcopy(config)
     name = config.pop('name')
-    if not hasattr(torch.nn.functional, name):
-        raise ValueError(f'Unrecognized activation function name ({name}).')
-    act = getattr(torch.nn.functional, name)
-    return partial(act, **config)
+    if name == 'quick_gelu':
+        return quickgelu_activation
+    else:
+        if not hasattr(torch.nn.functional, name):
+            raise ValueError(f'Unrecognized activation function name ({name}).')
+        act = getattr(torch.nn.functional, name)
+        return partial(act, **config)
 
 
 _DEFAULT_ACT_FN = resolve_ffn_act_fn(_FFN_ACT_FN_DEFAULT)

tests/models/layers/test_ffn.py

@@ -0,0 +1,73 @@
+# Copyright 2024 MosaicML LLM Foundry authors
+# SPDX-License-Identifier: Apache-2.0
+
+import pytest
+import torch
+import torch.distributed as dist
+import torch.nn as nn
+
+from llmfoundry.models.layers.ffn import quickgelu_activation
+from llmfoundry.models.layers.layer_builders import build_ffn
+
+
+@pytest.mark.gpu
+def test_quickgelu_activation():
+    d_model = 32
+    expansion_ratio = 1
+    no_bias = True
+    ffn_config = {
+        'ffn_act_fn': {
+            'name': 'quick_gelu',
+        },
+        'ffn_type': 'mptmlp',
+    }
+    rank: int = dist.get_rank()
+    device_str = f'cuda:{rank}'
+    device: torch.device = torch.device(device_str)
+
+    ffn1 = build_ffn(
+        name=ffn_config['ffn_type'],
+        d_model=d_model,
+        expansion_ratio=expansion_ratio,
+        device=device_str,
+        bias=not no_bias,
+        ffn_kwargs=ffn_config,
+    )
+    assert (
+        ffn1.act == quickgelu_activation
+    ), f'Expected quick_gelu activation function, got {ffn1.act}'
+
+    ffn_config = {
+        'ffn_act_fn': {
+            'name': 'gelu',
+        },
+        'ffn_type': 'mptmlp',
+    }
+    ffn2 = build_ffn(
+        name=ffn_config['ffn_type'],
+        d_model=d_model,
+        expansion_ratio=expansion_ratio,
+        device=device_str,
+        bias=not no_bias,
+        ffn_kwargs=ffn_config,
+    )
+
+    def num_params(model: nn.Module) -> int:
+        model_parameters = filter(lambda p: p.requires_grad, model.parameters())
+        return sum([p.numel() for p in model_parameters])
+
+    ffn1_numparams = num_params(ffn1)
+    ffn2_numparams = num_params(ffn2)
+    assert (
+        ffn1_numparams == ffn2_numparams
+    ), 'Only activation paths should have changed, re-check modeling!'
+
+    input_ = torch.rand(1, d_model, device=device)
+    output1 = ffn1(input_)
+    output2 = ffn2(input_)
+    assert (
+        output1.numel() == output2.numel()
+    ), 'Only activation paths should have changed, re-check modeling!'
+    assert (
+        not torch.allclose(output1, output2)
+    ), 'Functions are different, outputs should not match!'