[Bugfix] fix logging and d2h bug for flash comm1 (#3505)

### What this PR does / why we need it?

Fix 3 bugs in flash comm1 of Allgather
EP(https://github.com/vllm-project/vllm-ascend/pull/3334):
1. call `enable_sp()` with argument `vllm_config` trigger a lot of
warning log, this PR caches its return value.
2. `num_tokens_after_padding` should be cpu tensor as it will used as
`num_tokens_across_dp_cpu` in `DPMetadata`. It will causes may d2h copy
when running model.
3. In PD, model runner will execute `kv_connector_no_forward`，where
`num_tokens` is None

- vLLM version: v0.11.0rc3
- vLLM main: https://github.com/vllm-project/vllm/commit/v0.11.0

---------

Signed-off-by: realliujiaxu <realliujiaxu@163.com>

vllm_ascend/ascend_forward_context.py

@@ -114,7 +114,7 @@ def set_ascend_forward_context(
         # the performance may degrade due to the switching of communication methods.
         if is_moe_model(vllm_config):
             sp_enabled = enable_sp(vllm_config) and \
-                tp_world_size > 1
+                tp_world_size > 1 and num_tokens is not None
         else:
             sp_enabled = enable_sp(vllm_config) and \
                 tp_world_size > 1 and \

vllm_ascend/utils.py

@@ -56,6 +56,7 @@ _ASCEND_CUSTOMOP_IS_REIGISTERED = False
 _DEFAULT_BUFFER_SIZE = 200
 _MIN_DP_BUFFER_SIZE = 50
 _IS_MOE_MODEL = None
+_ENABLE_SP = None
 
 
 def is_310p():
@@ -606,15 +607,20 @@ def dense_optim_enable() -> bool:
 
 
 def enable_sp(vllm_config=None) -> bool:
-    if vllm_config is None:
-        from vllm.config import get_current_vllm_config
-        vllm_config = get_current_vllm_config()
-    return (
-        vllm_config.compilation_config.pass_config.enable_sequence_parallelism
-        or envs_ascend.VLLM_ASCEND_ENABLE_FLASHCOMM1
-        # Flash comm 1 should be enabled by env VLLM_ASCEND_ENABLE_FLASHCOMM1
-        # We retain the env VLLM_ASCEND_ENABLE_FLASHCOMM here for backward compatibility.
-        or bool(int(os.getenv("VLLM_ASCEND_ENABLE_FLASHCOMM", '0'))))
+    global _ENABLE_SP
+    if _ENABLE_SP is None:
+        if vllm_config is None:
+            from vllm.config import get_current_vllm_config
+            vllm_config = get_current_vllm_config()
+        _ENABLE_SP = (
+            vllm_config.compilation_config.pass_config.
+            enable_sequence_parallelism
+            or envs_ascend.VLLM_ASCEND_ENABLE_FLASHCOMM1
+            # Flash comm 1 should be enabled by env VLLM_ASCEND_ENABLE_FLASHCOMM1
+            # We retain the env VLLM_ASCEND_ENABLE_FLASHCOMM here for backward compatibility.
+            or bool(int(os.getenv("VLLM_ASCEND_ENABLE_FLASHCOMM", '0'))))
+
+    return _ENABLE_SP
 
 
 # TODO remove it after vllm has this func

vllm_ascend/worker/model_runner_v1.py

@@ -815,7 +815,7 @@ class NPUModelRunner(LoRAModelRunnerMixin):
         # Create a tensor for num_tokens_after_padding
         num_tokens_after_padding = torch.tensor([max_tokens_across_dp] *
                                                 self.dp_size,
-                                                device="npu",
+                                                device="cpu",
                                                 dtype=torch.int32)
 
         return max_tokens_across_dp, num_tokens_after_padding, global_with_prefill, global_enable_dbo