add warning to pp (#54448)

python/paddle/distributed/fleet/meta_parallel/pipeline_parallel.py

@@ -10,6 +10,7 @@
 # distributed under the License is distributed on an "AS IS" BASIS,
 # WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 # See the License for the specific language governing permissions and
+import warnings
 
 import paddle
 from paddle import framework
@@ -614,6 +615,10 @@ class PipelineParallelWithInterleave(PipelineParallel):
     def __init__(self, layers, hcg, strategy):
         super().__init__(layers=layers, hcg=hcg, strategy=strategy)
         assert layers.get_num_virtual_stages() > 1
+        if self.num_stages <= 2:
+            warnings.warn(
+                "Deprecate warning! In the near future the virtual pp will only available when pp degree > 2."
+            )
         assert (
             framework.in_dynamic_mode()
         ), "virtual pipeline stage with interleave only support eager dygraph mode"