update idefics2_vision_model.py

vllm/model_executor/models/idefics2_vision_model.py

@@ -23,7 +23,17 @@ import torch
 from torch import nn
 from transformers.models.idefics2.configuration_idefics2 import (
     Idefics2Config, Idefics2VisionConfig)
-from xformers import ops as xops
+# from xformers import ops as xops
+import vllm.envs as envs
+
+try:
+    if envs.VLLM_ATTENTION_BACKEND=="XFormers":
+        from xformers import ops as xops
+    else:
+        print("INFO: VLLM_ATTENTION_BACKEND is not XFormers.\n") 
+except ImportError:
+    print("INFO: Please install xformers if you want to infer pixtral.\n") 
+
 
 from vllm.distributed import divide, get_tensor_model_parallel_world_size
 from vllm.model_executor.layers.activation import get_act_fn