Fixing RmsNorm to fix #2380 and noticed with aimv2 when comparing out…

…puts. Still some work to do, need to look at AMP / fast mode behaviour, dispatch to torch when possible. Add SimpleNorm for 'LayerNorm w/o centering and bias'

timm/layers/__init__.py

@@ -34,7 +34,7 @@
 from .mixed_conv2d import MixedConv2d
 from .mlp import Mlp, GluMlp, GatedMlp, SwiGLU, SwiGLUPacked, ConvMlp, GlobalResponseNormMlp
 from .non_local_attn import NonLocalAttn, BatNonLocalAttn
-from .norm import GroupNorm, GroupNorm1, LayerNorm, LayerNorm2d, RmsNorm, RmsNorm2d
+from .norm import GroupNorm, GroupNorm1, LayerNorm, LayerNorm2d, RmsNorm, RmsNorm2d, SimpleNorm, SimpleNorm2d
 from .norm_act import BatchNormAct2d, GroupNormAct, GroupNorm1Act, LayerNormAct, LayerNormAct2d,\
     SyncBatchNormAct, convert_sync_batchnorm, FrozenBatchNormAct2d, freeze_batch_norm_2d, unfreeze_batch_norm_2d
 from .padding import get_padding, get_same_padding, pad_same

timm/layers/fast_norm.py

@@ -108,22 +108,24 @@ def fast_layer_norm(
         return F.layer_norm(x, normalized_shape, weight, bias, eps)
 
 
+
 def rms_norm(
     x: torch.Tensor,
     normalized_shape: List[int],
     weight: Optional[torch.Tensor] = None,
     eps: float = 1e-5,
 ):
     norm_ndim = len(normalized_shape)
+    v = x.pow(2)
     if torch.jit.is_scripting():
         # ndim = len(x.shape)
         # dims = list(range(ndim - norm_ndim, ndim))  # this doesn't work on pytorch <= 1.13.x
         # NOTE -ve dims cause torchscript to crash in some cases, out of options to work around
         assert norm_ndim == 1
-        v = torch.var(x, dim=-1).unsqueeze(-1)  # ts crashes with -ve dim + keepdim=True
+        v = torch.mean(v, dim=-1).unsqueeze(-1)  # ts crashes with -ve dim + keepdim=True
     else:
         dims = tuple(range(-1, -norm_ndim - 1, -1))
-        v = torch.var(x, dim=dims, keepdim=True)
+        v = torch.mean(v, dim=dims, keepdim=True)
     x = x * torch.rsqrt(v + eps)
     if weight is not None:
         x = x * weight
@@ -148,3 +150,47 @@ def fast_rms_norm(
 
     # fallback
     return rms_norm(x, normalized_shape, weight, eps)
+
+
+def simple_norm(
+    x: torch.Tensor,
+    normalized_shape: List[int],
+    weight: Optional[torch.Tensor] = None,
+    eps: float = 1e-5,
+):
+    norm_ndim = len(normalized_shape)
+    if torch.jit.is_scripting():
+        # ndim = len(x.shape)
+        # dims = list(range(ndim - norm_ndim, ndim))  # this doesn't work on pytorch <= 1.13.x
+        # NOTE -ve dims cause torchscript to crash in some cases, out of options to work around
+        assert norm_ndim == 1
+        v = torch.var(x, dim=-1).unsqueeze(-1)  # ts crashes with -ve dim + keepdim=True
+    else:
+        dims = tuple(range(-1, -norm_ndim - 1, -1))
+        v = torch.var(x, dim=dims, keepdim=True)
+    x = x * torch.rsqrt(v + eps)
+    if weight is not None:
+        x = x * weight
+    return x
+
+
+def fast_simple_norm(
+    x: torch.Tensor,
+    normalized_shape: List[int],
+    weight: Optional[torch.Tensor] = None,
+    eps: float = 1e-5,
+) -> torch.Tensor:
+    if torch.jit.is_scripting():
+        # this must be by itself, cannot merge with has_apex_rmsnorm
+        return simple_norm(x, normalized_shape, weight, eps)
+
+    if is_autocast_enabled(x.device.type):
+        # normally native AMP casts LN inputs to float32
+        # apex LN does not, this is behaving like Apex
+        dt = get_autocast_dtype(x.device.type)
+        x, weight = x.to(dt), weight.to(dt)
+
+    with torch.amp.autocast(device_type=x.device.type, enabled=False):
+        x = simple_norm(x, normalized_shape, weight, eps)
+    return x
+

timm/layers/norm.py

@@ -11,7 +11,7 @@
 import torch.nn as nn
 import torch.nn.functional as F
 
-from .fast_norm import is_fast_norm, fast_group_norm, fast_layer_norm, fast_rms_norm
+from .fast_norm import is_fast_norm, fast_group_norm, fast_layer_norm, fast_rms_norm, fast_simple_norm
 
 
 class GroupNorm(nn.GroupNorm):
@@ -190,3 +190,73 @@ def forward(self, x: torch.Tensor) -> torch.Tensor:
         x = fast_rms_norm(x, self.normalized_shape, self.weight, self.eps)
         x = x.permute(0, 3, 1, 2)
         return x
+
+
+class SimpleNorm(nn.Module):
+    """ SimpleNorm (x / std(x))
+    """
+    __constants__ = ['normalized_shape', 'eps', 'elementwise_affine']
+    normalized_shape: Tuple[int, ...]
+    eps: float
+    elementwise_affine: bool
+
+    def __init__(self, channels, eps=1e-6, affine=True, device=None, dtype=None) -> None:
+        factory_kwargs = {'device': device, 'dtype': dtype}
+        super().__init__()
+        normalized_shape = channels
+        if isinstance(normalized_shape, numbers.Integral):
+            # mypy error: incompatible types in assignment
+            normalized_shape = (normalized_shape,)  # type: ignore[assignment]
+        self.normalized_shape = tuple(normalized_shape)  # type: ignore[arg-type]
+        self.eps = eps
+        self.elementwise_affine = affine
+        if self.elementwise_affine:
+            self.weight = nn.Parameter(torch.empty(self.normalized_shape, **factory_kwargs))
+        else:
+            self.register_parameter('weight', None)
+
+        self.reset_parameters()
+
+    def reset_parameters(self) -> None:
+        if self.elementwise_affine:
+            nn.init.ones_(self.weight)
+
+    def forward(self, x: torch.Tensor) -> torch.Tensor:
+        x = fast_simple_norm(x, self.normalized_shape, self.weight, self.eps)
+        return x
+
+
+class SimpleNorm2d(nn.Module):
+    """ SimpleNorm for NCHW tensors
+    """
+    __constants__ = ['normalized_shape', 'eps', 'elementwise_affine']
+    normalized_shape: Tuple[int, ...]
+    eps: float
+    elementwise_affine: bool
+
+    def __init__(self, channels, eps=1e-6, affine=True, device=None, dtype=None) -> None:
+        factory_kwargs = {'device': device, 'dtype': dtype}
+        super().__init__()
+        normalized_shape = channels
+        if isinstance(normalized_shape, numbers.Integral):
+            # mypy error: incompatible types in assignment
+            normalized_shape = (normalized_shape,)  # type: ignore[assignment]
+        self.normalized_shape = tuple(normalized_shape)  # type: ignore[arg-type]
+        self.eps = eps
+        self.elementwise_affine = affine
+        if self.elementwise_affine:
+            self.weight = nn.Parameter(torch.empty(self.normalized_shape, **factory_kwargs))
+        else:
+            self.register_parameter('weight', None)
+
+        self.reset_parameters()
+
+    def reset_parameters(self) -> None:
+        if self.elementwise_affine:
+            nn.init.ones_(self.weight)
+
+    def forward(self, x: torch.Tensor) -> torch.Tensor:
+        x = x.permute(0, 2, 3, 1)
+        x = fast_simple_norm(x, self.normalized_shape, self.weight, self.eps)
+        x = x.permute(0, 3, 1, 2)
+        return x

timm/models/convnext.py

@@ -46,6 +46,7 @@
 from timm.data import IMAGENET_DEFAULT_MEAN, IMAGENET_DEFAULT_STD, OPENAI_CLIP_MEAN, OPENAI_CLIP_STD
 from timm.layers import trunc_normal_, AvgPool2dSame, DropPath, Mlp, GlobalResponseNormMlp, \
     LayerNorm2d, LayerNorm, RmsNorm2d, RmsNorm, create_conv2d, get_act_layer, get_norm_layer, make_divisible, to_ntuple
+from timm.layers import SimpleNorm2d, SimpleNorm
 from timm.layers import NormMlpClassifierHead, ClassifierHead
 from ._builder import build_model_with_cfg
 from ._features import feature_take_indices
@@ -233,6 +234,34 @@ def forward(self, x):
             x = self.blocks(x)
         return x
 
+# map of norm layers with NCHW (2D) and channels last variants
+_NORM_MAP = {
+    'layernorm': (LayerNorm2d, LayerNorm),
+    'layernorm2d': (LayerNorm2d, LayerNorm),
+    'simplenorm': (SimpleNorm2d, SimpleNorm),
+    'simplenorm2d': (SimpleNorm2d, SimpleNorm),
+    'rmsnorm': (RmsNorm2d, RmsNorm),
+    'rmsnorm2d': (RmsNorm2d, RmsNorm),
+}
+
+
+def _get_norm_layers(norm_layer: Union[Callable, str], conv_mlp: bool, norm_eps: float):
+    norm_layer = norm_layer or 'layernorm'
+    if norm_layer in _NORM_MAP:
+        norm_layer_cl = _NORM_MAP[norm_layer][0] if conv_mlp else _NORM_MAP[norm_layer][1]
+        norm_layer = _NORM_MAP[norm_layer][0]
+        if norm_eps is not None:
+            norm_layer = partial(norm_layer, eps=norm_eps)
+            norm_layer_cl = partial(norm_layer_cl, eps=norm_eps)
+    else:
+        assert conv_mlp, \
+            'If a norm_layer is specified, conv MLP must be used so all norm expect rank-4, channels-first input'
+        norm_layer = get_norm_layer(norm_layer)
+        norm_layer_cl = norm_layer
+        if norm_eps is not None:
+            norm_layer_cl = partial(norm_layer_cl, eps=norm_eps)
+    return norm_layer, norm_layer_cl
+
 
 class ConvNeXt(nn.Module):
     r""" ConvNeXt
@@ -289,20 +318,7 @@ def __init__(
         super().__init__()
         assert output_stride in (8, 16, 32)
         kernel_sizes = to_ntuple(4)(kernel_sizes)
-        use_rms = isinstance(norm_layer, str) and norm_layer.startswith('rmsnorm')
-        if norm_layer is None or use_rms:
-            norm_layer = RmsNorm2d if use_rms else LayerNorm2d
-            norm_layer_cl = norm_layer if conv_mlp else (RmsNorm if use_rms else LayerNorm)
-            if norm_eps is not None:
-                norm_layer = partial(norm_layer, eps=norm_eps)
-                norm_layer_cl = partial(norm_layer_cl, eps=norm_eps)
-        else:
-            assert conv_mlp,\
-                'If a norm_layer is specified, conv MLP must be used so all norm expect rank-4, channels-first input'
-            norm_layer = get_norm_layer(norm_layer)
-            norm_layer_cl = norm_layer
-            if norm_eps is not None:
-                norm_layer_cl = partial(norm_layer_cl, eps=norm_eps)
+        norm_layer, norm_layer_cl = _get_norm_layers(norm_layer, conv_mlp, norm_eps)
         act_layer = get_act_layer(act_layer)
 
         self.num_classes = num_classes
@@ -975,7 +991,7 @@ def _cfgv2(url='', **kwargs):
 @register_model
 def convnext_zepto_rms(pretrained=False, **kwargs) -> ConvNeXt:
     # timm femto variant (NOTE: still tweaking depths, will vary between 3-4M param, current is 3.7M
-    model_args = dict(depths=(2, 2, 4, 2), dims=(32, 64, 128, 256), conv_mlp=True, norm_layer='rmsnorm2d')
+    model_args = dict(depths=(2, 2, 4, 2), dims=(32, 64, 128, 256), conv_mlp=True, norm_layer='simplenorm')
     model = _create_convnext('convnext_zepto_rms', pretrained=pretrained, **dict(model_args, **kwargs))
     return model
 
@@ -984,7 +1000,7 @@ def convnext_zepto_rms(pretrained=False, **kwargs) -> ConvNeXt:
 def convnext_zepto_rms_ols(pretrained=False, **kwargs) -> ConvNeXt:
     # timm femto variant (NOTE: still tweaking depths, will vary between 3-4M param, current is 3.7M
     model_args = dict(
-        depths=(2, 2, 4, 2), dims=(32, 64, 128, 256), conv_mlp=True, norm_layer='rmsnorm2d', stem_type='overlap_act')
+        depths=(2, 2, 4, 2), dims=(32, 64, 128, 256), conv_mlp=True, norm_layer='simplenorm', stem_type='overlap_act')
     model = _create_convnext('convnext_zepto_rms_ols', pretrained=pretrained, **dict(model_args, **kwargs))
     return model