Do not fuse split_heads with qkv

This is most likely due to bitsandbytes performing work not captured in the graph

src/petals/models/falcon/block.py

@@ -148,29 +148,27 @@ def __init__(self, config: FalconConfig):
             self._split_heads = partial(
                 split_heads, num_heads=self.num_heads, num_kv_heads=self.num_kv_heads, head_dim=self.head_dim
             )
-            self.qkv_graph = None
+            self.split_graph = None
             self.input_surface = None
             self.static_outputs = None
 
-    def _optimized_apply_qkv(self, hidden_states):
-        if self.qkv_graph is None:
-            self.qkv_graph = torch.cuda.CUDAGraph()
-            self.input_surface = torch.randn_like(hidden_states)
+    def _optimized_split_heads(self, fused_qkv):
+        if self.split_graph is None:
+            self.split_graph = torch.cuda.CUDAGraph()
+            self.input_surface = fused_qkv
 
             s = torch.cuda.Stream()
             s.wait_stream(torch.cuda.current_stream())
             with torch.cuda.stream(s):
                 for _ in range(3):
-                    fused_qkv = self.query_key_value(self.input_surface)
                     self._split_heads(fused_qkv)
             torch.cuda.current_stream().wait_stream(s)
 
-            with torch.cuda.graph(self.qkv_graph):
-                static_fused_qkv = self.query_key_value(self.input_surface)
-                self.static_outputs = self._split_heads(static_fused_qkv)
+            with torch.cuda.graph(self.split_graph):
+                self.static_outputs = self._split_heads(self.input_surface)
 
-        self.input_surface.copy_(hidden_states)
-        self.qkv_graph.replay()
+        self.input_surface.copy_(fused_qkv)
+        self.split_graph.replay()
         return tuple(o.detach() for o in self.static_outputs)
 
     def forward(
@@ -185,15 +183,16 @@ def forward(
     ):
         assert not output_attentions
 
+        fused_qkv = self.query_key_value(hidden_states)  # [batch_size, seq_length, 3 x hidden_size]
+
         if (
             self.new_decoder_architecture
             and hidden_states.size(1) == 1
             and torch.is_inference_mode_enabled()
             and hidden_states.device.type == "cuda"
         ):
-            query_layer, key_layer, value_layer = self._optimized_apply_qkv(hidden_states)
+            query_layer, key_layer, value_layer = self._optimized_split_heads(fused_qkv)
         else:
-            fused_qkv = self.query_key_value(hidden_states)  # [batch_size, seq_length, 3 x hidden_size]
             # 3 x [batch_size, seq_length, num_heads, head_dim]
             (query_layer, key_layer, value_layer) = self._split_heads(fused_qkv)