Copy changes made to Megatron-LM (#372)

Signed-off-by: Asha Anoosheh <[email protected]>

Author: AAnoosheh

modelopt/torch/distill/plugins/megatron.py

@@ -59,7 +59,7 @@ class DistillationConfig:
         logit_kl_temperature: Temperature for the logit KL-divergence loss.
     """
 
-    intermediate_layer_pairs: list[tuple[str, str]] = field(default_factory=list)
+    intermediate_layer_pairs: list[tuple[str, ...]] = field(default_factory=list)
     logit_layers: tuple[str, str] = ("output_layer", "output_layer")
     skip_lm_loss: bool = True
     kd_loss_scale: float = 1.0
@@ -69,12 +69,28 @@ class DistillationConfig:
 
     def __post_init__(self):
         assert len(self.logit_layers) == 2, f"{self.logit_layers=}"
-        assert all(len(pair) == 2 for pair in self.intermediate_layer_pairs), (
+        assert all(len(pair) in (2, 3) for pair in self.intermediate_layer_pairs), (
             f"{self.intermediate_layer_pairs=}"
         )
         assert self.kd_loss_scale > 0, f"{self.kd_loss_scale=}"
         assert self.logit_kl_temperature > 0, f"{self.logit_kl_temperature=}"
 
+    @staticmethod
+    def parse_intermediate_entry(entry: tuple[str, ...]) -> tuple[str, str, Callable]:
+        """Parse an intermediate entry into a student layer, teacher layer, and loss function."""
+        if len(entry) == 3:
+            student_layer, teacher_layer, loss_fn_name = entry
+            if loss_fn_name == "cosine":
+                loss_fn = HiddenStateCosineLoss
+            elif loss_fn_name == "mse":
+                loss_fn = MSELoss
+            else:
+                raise ValueError(f"Unknown intermediate loss function: {loss_fn_name}")
+        else:
+            student_layer, teacher_layer = entry
+            loss_fn = HiddenStateCosineLoss  # default to cosine loss
+        return student_layer, teacher_layer, loss_fn
+
 
 def load_distillation_config(
     config_path: str | None, student_cfg: "TransformerConfig", teacher_cfg: "TransformerConfig"
@@ -105,7 +121,8 @@ def load_distillation_config(
         # NOTE: Projection layer shared among intermediate layer pairs.
         projection_layer = ProjectionLayer(student_cfg, teacher_cfg)
 
-        for student_layer, teacher_layer in cfg.intermediate_layer_pairs:
+        for entry in cfg.intermediate_layer_pairs:
+            student_layer, teacher_layer, loss_fn = cfg.parse_intermediate_entry(entry)
             if parallel_state.get_tensor_and_context_parallel_rank() == 0:
                 logger.info(
                     "Distillation: Adding intermediate loss between"
@@ -114,7 +131,7 @@ def load_distillation_config(
                 )
             student_layer = _adjust_layer_index_for_pp(student_layer, student_cfg)
             teacher_layer = _adjust_layer_index_for_pp(teacher_layer, teacher_cfg)
-            criterion[(student_layer, teacher_layer)] = HiddenStateCosineLoss(
+            criterion[(student_layer, teacher_layer)] = loss_fn(
                 student_cfg, projection_layer=projection_layer
             )
 
@@ -202,9 +219,9 @@ def forward(self, predictions: Tensor, targets: Tensor) -> Tensor:
         predictions, targets = self.pre_forward(predictions, targets)
 
         loss = F.mse_loss(predictions, targets, reduction="none")
-        loss = loss.sum(dim=-1)
+        loss = loss.mean(dim=-1)
 
-        return self.post_forward(loss)
+        return self.post_forward(loss, is_sequence_parallel=self._config.sequence_parallel)
 
 
 class HiddenStateCosineLoss(BaseLoss):