[None][feat] Add llama4 scaling (#9771)

Signed-off-by: bhsueh <11360707+byshiue@users.noreply.github.com>

Author: byshiue

tensorrt_llm/_torch/modules/attention.py

@@ -985,6 +985,14 @@ def yarn_get_mscale(scale=1, mscale=1):
                 is_neox=pos_embd_params.is_neox,
             )
 
+        self.llama_4_scaling = False
+        if hasattr(config.pretrained_config, 'llama_4_scaling'):
+            self.llama_4_scaling = True
+            self.floor_scale = getattr(config.pretrained_config.llama_4_scaling,
+                                       'original_max_position_embeddings', 8192)
+            self.attn_scale = getattr(config.pretrained_config.llama_4_scaling,
+                                      'beta', 0.1)
+
         if not config.skip_create_weights_in_init:
             self.create_weights()
 
@@ -1127,6 +1135,18 @@ def create_output(self, hidden_states: torch.Tensor, num_contexts: int):
         return hidden_states.new_empty([num_tokens, hidden_size],
                                        dtype=hidden_states.dtype)
 
+    def _attention_scaling(self, q, position_ids):
+
+        def _get_attn_scale(position_ids: torch.Tensor) -> torch.Tensor:
+            positions = position_ids.view(-1)
+            floor = torch.floor((positions + 1.0) / self.floor_scale)
+            attn_scale = torch.log(floor + 1.0) * self.attn_scale + 1.0
+            return attn_scale.unsqueeze(-1)
+
+        attn_scale = _get_attn_scale(position_ids)
+        q = (q * attn_scale).to(q.dtype)
+        return q
+
     def forward_impl(self,
                      position_ids: Optional[torch.Tensor],
                      hidden_states: torch.Tensor,
@@ -1197,6 +1217,10 @@ def forward_impl(self,
                 assert position_ids is not None
                 k_pe_ctx = self.apply_rope(q_ctx, k_pe_ctx, position_ids)
 
+            if self.llama_4_scaling:
+                q_ctx = self._attention_scaling(
+                    q_ctx, position_ids[..., :num_ctx_tokens])
+
             self.forward_context(
                 q_ctx,
                 compressed_kv_ctx,
@@ -1217,6 +1241,10 @@ def forward_impl(self,
                 assert position_ids is not None
                 k_pe_gen = self.apply_rope(q_gen, k_pe_gen, position_ids)
 
+            if self.llama_4_scaling:
+                q_gen = self._attention_scaling(
+                    q_gen, position_ids[..., num_ctx_tokens:])
+
             self.forward_absorption_generation(
                 q_gen,
                 compressed_kv_gen,