[diffusion] chore: remove redundant ulysses nccl warmup (#16301)

python/sglang/multimodal_gen/runtime/distributed/parallel_state.py

@@ -32,7 +32,6 @@ If you only need to use the distributed environment without model parallelism,
 """
 import contextlib
 import os
-import time
 import weakref
 from collections import namedtuple
 from collections.abc import Callable
@@ -434,9 +433,6 @@ def initialize_model_parallel(
         ring_group=PROCESS_GROUP.RING_PG,
     )
 
-    if ulysses_degree > 1:
-        _warmup_ulysses_communication()
-
     global _TP
     assert _TP is None, "Tensor parallel group is already initialized"
     _TP = init_parallel_group_coordinator(
@@ -949,49 +945,6 @@ def get_ring_parallel_rank():
     return get_sp_group().ring_rank
 
 
-def _warmup_ulysses_communication():
-    """
-    Warmup NCCL communication for Ulysses all-to-all to avoid first-step latency.
-
-    This function performs a dummy all-to-all operation to initialize NCCL communication
-    channels, which can take several seconds on the first call.
-    """
-    logger.info("Warming up Ulysses all-to-all communication...")
-
-    try:
-        import torch.distributed._functional_collectives as ft_c
-
-        ulysses_pg = get_sp_group().ulysses_group
-        if ulysses_pg is None:
-            logger.warning("Ulysses group not initialized, skipping warmup")
-            return
-
-        warmup_start = time.time()
-
-        device = torch.device(f"cuda:{get_world_group().local_rank}")
-        dummy_tensor = torch.zeros(1024, device=device, dtype=torch.float32)
-
-        output = ft_c.all_to_all_single(
-            dummy_tensor,
-            output_split_sizes=None,
-            input_split_sizes=None,
-            group=ulysses_pg,
-        )
-
-        if isinstance(output, ft_c.AsyncCollectiveTensor):
-            output = output.wait()
-
-        torch.cuda.synchronize()
-
-        warmup_time = (time.time() - warmup_start) * 1000
-        logger.info(f"Ulysses communication warmup completed in {warmup_time:.2f}ms")
-
-    except Exception as e:
-        logger.warning(
-            f"Ulysses communication warmup failed: {e}. Continuing without warmup."
-        )
-
-
 # PP
 def get_pp_group() -> PipelineGroupCoordinator:
     assert _PP is not None, "pipeline model parallel group is not initialized"