[Bugfix] [diffusion] Fix cache-dit with sp-degree only (#19965)

Co-authored-by: Mick <mickjagger19@icloud.com>
Co-authored-by: ronnie_zheng <zl19940307@163.com>

python/sglang/multimodal_gen/runtime/cache/cache_dit_integration.py

@@ -12,6 +12,11 @@ from typing import List, Optional
 import torch
 import torch.distributed as dist
 
+from sglang.multimodal_gen.runtime.distributed.parallel_state import (
+    get_ring_parallel_world_size,
+    get_tp_world_size,
+    get_ulysses_parallel_world_size,
+)
 from sglang.multimodal_gen.runtime.utils.logging_utils import init_logger
 
 logger = init_logger(__name__)
@@ -107,15 +112,15 @@ def _build_parallelism_config(
     ulysses_size = None
     ring_size = None
     if sp_group is not None:
-        ulysses_size = getattr(sp_group, "ulysses_world_size", None)
-        ring_size = getattr(sp_group, "ring_world_size", None)
+        ulysses_size = get_ulysses_parallel_world_size()
+        ring_size = get_ring_parallel_world_size()
 
     tp_size = None
     if tp_group is not None:
-        tp_size = dist.get_world_size(tp_group)
+        tp_size = get_tp_world_size()
 
     return ParallelismConfig(
-        backend=ParallelismBackend.NATIVE_PYTORCH,
+        backend=ParallelismBackend.AUTO,
         ulysses_size=ulysses_size,
         ring_size=ring_size,
         tp_size=tp_size,