Add dtype, fix RMS norm for FP16 (#8641)

* Add dtype, fix RMS norm for FP16

* up

* up

* Update llama_transformer.py

Author: metascroy

examples/apple/coreml/llama/export.py

@@ -3,7 +3,6 @@
 # pyre-strict
 
 import argparse
-import json
 
 import sys
 
@@ -20,10 +19,11 @@
 from executorch.exir.passes import MemoryPlanningPass
 from executorch.exir.passes.quant_fusion_pass import QuantFusionPass
 from executorch.exir.passes.sym_shape_eval_pass import ConstraintBasedSymShapeEvalPass
-from executorch.extension.export_util.utils import export_to_edge, save_pte_program
+from executorch.exir.program._program import to_edge_with_preserved_ops
+from executorch.extension.export_util.utils import save_pte_program
 
 sys.path.insert(0, ".")
-from llama_transformer import InputManager, ModelArgs, Transformer
+from llama_transformer import InputManager, load_model
 
 
 class SplitLinearModule(torch.nn.Module):
@@ -141,42 +141,23 @@ def main() -> None:
         default=8,
         help="Maximum number of splits to divide linear layers",
     )
+    parser.add_argument(
+        "--dtype",
+        type=str,
+        default="fp16",
+    )
 
     export_args = parser.parse_args()
-    params_path = export_args.params
-    checkpoint_path = export_args.checkpoint
-
-    # Load model args
-    with open(params_path, "r") as f:
-        params = json.loads(f.read())
-
-    args = ModelArgs(
-        max_seq_len=export_args.max_seq_length,
-        generate_full_logits=False,
+    model = load_model(
+        export_args.checkpoint,
+        export_args.params,
+        max_seq_length=export_args.max_seq_length,
         use_cache_list=export_args.use_cache_list,
-        **params,
-    )
-
-    with torch.device("meta"):
-        model = Transformer(args)
-
-    checkpoint = torch.load(
-        checkpoint_path, map_location="cpu", mmap=True, weights_only=True
     )
-    if "model" in checkpoint:
-        checkpoint = checkpoint["model"]
 
-    missing, unexpected = model.load_state_dict(
-        checkpoint,
-        strict=False,
-        assign=True,
-    )
-    print("Missing keys: ", missing)
-    print("Unexpected keys: ", unexpected)
-
-    float_dtype = torch.float16  # dtype for model/inputs
-    model.eval()
-    model.to(float_dtype)
+    float_dtype = {"fp16": torch.float16, "fp32": torch.float32}[
+        export_args.dtype
+    ]  # dtype for model/inputs
 
     if export_args.embedding_quantize:
         bitwidth, group_size = export_args.embedding_quantize.split(",")
@@ -197,7 +178,8 @@ def main() -> None:
             model, export_args.target_split_size, export_args.max_splits
         )
 
-    model = model.to(float_dtype)
+    model.eval()
+    model.to(float_dtype)
 
     op_linear_quantizer_config = None
     if export_args.coreml_quantize == "b4w":
@@ -217,7 +199,10 @@ def main() -> None:
 
     compile_specs = CoreMLBackend.generate_compile_specs(  # pyre-fixme[16]
         minimum_deployment_target=ct.target.iOS18,
-        compute_precision=ct.precision(ct.precision.FLOAT16.value),
+        compute_precision={
+            torch.float16: ct.precision.FLOAT16,
+            torch.float32: ct.precision.FLOAT32,
+        }[float_dtype],
         compute_unit=ct.ComputeUnit.CPU_AND_NE,
         model_type=CoreMLBackend.MODEL_TYPE.MODEL,  # pyre-fixme[16]
         op_linear_quantizer_config=op_linear_quantizer_config,
@@ -232,11 +217,11 @@ def main() -> None:
     )
 
     input_manager = InputManager(
-        n_layers=args.n_layers,
-        max_batch_size=args.max_batch_size,
-        n_kv_heads=args.n_kv_heads,
-        max_seq_length=args.max_seq_len,
-        head_dim=args.head_dim,
+        n_layers=model.params.n_layers,
+        max_batch_size=model.params.max_batch_size,
+        n_kv_heads=model.params.n_kv_heads,
+        max_seq_length=model.params.max_seq_len,
+        head_dim=model.params.head_dim,
         use_cache_list=export_args.use_cache_list,
         seq_length=export_args.seq_length,
         dtype=float_dtype,
@@ -245,10 +230,20 @@ def main() -> None:
     )
     example_inputs = input_manager.get_inputs(tokens=[0])
 
-    edge_manager = export_to_edge(
+    ep = torch.export.export(
         model,
         example_inputs,
-        edge_compile_config=EdgeCompileConfig(
+    )
+    print("Exported program")
+    print(ep)
+
+    edge_manager = to_edge_with_preserved_ops(
+        ep,
+        preserve_ops=[
+            torch.ops.aten.scaled_dot_product_attention.default,
+            torch.ops.aten.linalg_vector_norm.default,
+        ],
+        compile_config=EdgeCompileConfig(
             _check_ir_validity=False,
             _skip_type_promotion=(float_dtype == torch.float16),
             _skip_dim_order=True,

examples/apple/coreml/llama/llama_transformer.py

@@ -13,8 +13,6 @@
 import torch
 import torch.nn.functional as F
 
-from executorch.examples.models.llama.llama_transformer import RMSNorm
-
 from executorch.examples.models.llama.rope import (
     hf_apply_rotary_emb,
     hf_precompute_freqs_cis,
@@ -25,29 +23,6 @@
 from torch import nn
 
 
-# These are just to prevent to_edge from decomposing SDPA
-# A better method is to use the to_edge_transform_and_lower API for CoreML
-# and not decompose SDPA
-@torch.library.custom_op("coreml::sdpa", mutates_args=())
-def sdpa(
-    q: torch.Tensor, k: torch.Tensor, v: torch.Tensor, attn_mask: torch.Tensor
-) -> torch.Tensor:
-    """Same as F.scaled_dot_product_attention, but with custom op to avoid lowering during dialect conversion."""
-    return torch.ops.aten.scaled_dot_product_attention.default(
-        q, k, v, attn_mask=attn_mask
-    )
-
-
-@torch.library.register_fake("coreml::sdpa")
-def _(
-    q: torch.Tensor, k: torch.Tensor, v: torch.Tensor, attn_mask: torch.Tensor
-) -> torch.Tensor:
-    """Fake implementation with the right output shape, which is required for torch.compile/export/fx tracing."""
-    expected_shape = list(q.shape)
-    expected_shape[-1] = v.shape[-1]
-    return q.new_empty(expected_shape)
-
-
 def find_multiple(n: int, k: int) -> int:
     if n % k == 0:
         return n
@@ -121,6 +96,63 @@ def __post_init__(self):
             self.head_dim = self.dim // self.n_heads
 
 
+class RMSNorm(torch.nn.Module):
+    def __init__(self, dim: int, eps: float = 1e-6):
+        """
+        Initialize the RMSNorm normalization layer.
+
+        Args:
+            dim (int): The dimension of the input tensor.
+            eps (float, optional): A small value added to the denominator for numerical stability. Default is 1e-6.
+
+        Attributes:
+            eps (float): A small value added to the denominator for numerical stability.
+            weight (nn.Parameter): Learnable scaling parameter.
+
+        """
+        super().__init__()
+        self.dim = dim
+        self.eps = eps
+        self.weight = nn.Parameter(torch.ones(dim))
+
+    def _norm(self, x):
+        """
+        Apply the RMSNorm normalization to the input tensor.
+
+        Args:
+            x (torch.Tensor): The input tensor.
+
+        Returns:
+            torch.Tensor: The normalized tensor.
+
+        """
+        # CoreML ignores casts to FP32, so existing implementation of RMSNorm was not stable
+        # We instead use (x * sqrt(n)) / norm(x, dim=-1)
+        # Using torch.norm and preserving this op in CoreML improves stability
+        # Note, we ignore eps, but could add it by using torch.norm(torch.concat(x, sqrt(n*eps))) in the denominator
+        # In future, we want to add CoreML support for the functional RMSNorm op
+        # We have yet to do large scale evaluations on the numeric stability of this solution, but note that
+        # it appears better than what exists currently (removing FP32 casts and using FP16)
+        rms_norm_eps0 = (
+            x * torch.sqrt(torch.tensor(self.dim, dtype=x.dtype))
+        ) / torch.linalg.vector_norm(x, dim=-1, keepdim=True)
+        return rms_norm_eps0
+
+    def forward(self, x):
+        """
+        Forward pass through the RMSNorm layer.
+
+        Args:
+            x (torch.Tensor): The input tensor.
+
+        Returns:
+            torch.Tensor: The output tensor after applying RMSNorm.
+
+        """
+        output = self._norm(x)
+        return output * self.weight
+
+
 class Rope(torch.nn.Module):
     def __init__(self, params: ModelArgs):
         super().__init__()
@@ -304,12 +336,11 @@ def forward(
             k = k.repeat_interleave(self.n_rep, dim=1)
             v = v.repeat_interleave(self.n_rep, dim=1)
 
-        output = torch.ops.coreml.sdpa(q, k, v, attn_mask)
-
+        output = torch.ops.aten.scaled_dot_product_attention.default(
+            q, k, v, attn_mask=attn_mask
+        )
         output = output.transpose(1, 2).contiguous().view(bsz, seqlen, -1)
-
         output = self.wo(output)
-
         return output, new_k, new_v
 
 
@@ -413,6 +444,39 @@ def forward(
         return logits, k_out, v_out
 
 
+def load_model(checkpoint_path, params_path, max_seq_length, use_cache_list):
+    import json
+
+    with open(params_path, "r") as f:
+        params = json.loads(f.read())
+
+    args = ModelArgs(
+        max_seq_len=max_seq_length,
+        generate_full_logits=False,
+        use_cache_list=use_cache_list,
+        **params,
+    )
+
+    with torch.device("meta"):
+        model = Transformer(args)
+
+    checkpoint = torch.load(
+        checkpoint_path, map_location="cpu", mmap=True, weights_only=True
+    )
+    if "model" in checkpoint:
+        checkpoint = checkpoint["model"]
+
+    missing, unexpected = model.load_state_dict(
+        checkpoint,
+        strict=False,
+        assign=True,
+    )
+    print("Missing keys: ", missing)
+    print("Unexpected keys: ", unexpected)
+
+    return model
+
+
 class InputManager:
     def __init__(
         self,

examples/apple/coreml/llama/readme.md

@@ -4,7 +4,7 @@ This directory contains ANE-friendly Llama models.
 
 Export model with:
 ```
-python export.py -n /path/to/output/model.pte -p /path/to/params.json -c /path/to/model.pth --seq_length 64 --max_seq_length 1024 --coreml-quantize c4w
+python export.py -n /path/to/output/model.pte -p /path/to/params.json -c /path/to/model.pth --seq_length 64 --max_seq_length 1024 --coreml-quantize c4w --dtype fp16
 ```
 
 (Note the script should be run from the executorch/examples/apple/coreml/llama directory.)
@@ -17,6 +17,12 @@ Run model with:
 python run.py -m /path/to/model.pte -t /path/to/tokenizer.model --prompt "Once upon a time,"
 ```
 
+The runner can also be used to run an eager model model to compare with CoreML numerics (--use_eager).  In this case, you must specify:
+* --checkpoint
+* --dtype
+* --max_seq_length
+* --seq_length
+
 (Note the script should be run from the executorch/examples/apple/coreml/llama directory.)