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[None][fix] Better error message for mismatched MPI world size #11294

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[None][fix] Better error message for mismatched MPI world size #11294

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8c32fb4
better error message with mismatched mpi world size
jthomson04 Feb 4, 2026
75759dd
fixes
jthomson04 Feb 5, 2026
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19 changes: 18 additions & 1 deletion tensorrt_llm/_torch/distributed/communicator.py
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Original file line number Diff line number Diff line change
Expand Up @@ -20,7 +20,8 @@
from tensorrt_llm._utils import (mpi_allgather, mpi_barrier, mpi_comm,
mpi_disabled, mpi_isend, mpi_isend_object,
mpi_recv, mpi_recv_object, mpi_send,
mpi_send_object, torch_pybind11_abi)
mpi_send_object, mpi_world_size,
torch_pybind11_abi)
from tensorrt_llm.bindings.BuildInfo import ENABLE_MULTI_DEVICE
from tensorrt_llm.bindings.internal.process_group import init_pg
from tensorrt_llm.logger import logger
Expand Down Expand Up @@ -456,6 +457,19 @@ def __init__(self, mapping: Mapping):
self._tp_comm = None
self._pp_comm = None

def _validate_world_size(self):
"""Validate world size before creating sub-communicators to prevent segfaults."""

if ENABLE_MULTI_DEVICE:
actual_world_size = mpi_world_size()
max_rank_needed = self.mapping.world_size

if max_rank_needed > actual_world_size:
raise RuntimeError(
f"Mapping requires world_size={max_rank_needed} "
f"(tp_size={self.mapping.tp_size} * pp_size={self.mapping.pp_size} * cp_size={self.mapping.cp_size}), "
f"but MPI world size is only {actual_world_size}. ")

def broadcast(self, obj, root=0, chunk_size: int = 4 * 1024 * 1024):
comm = mpi_comm()
return safe_broadcast(comm, obj, root=root, chunk_size=chunk_size)
Expand Down Expand Up @@ -493,6 +507,7 @@ def recv_object(self, src, tag=0):
@property
def tp_comm(self):
if self._tp_comm is None:
self._validate_world_size()
mapping = self.mapping
new_group = mpi_comm().group.Incl(mapping.tp_group)
self._tp_comm = mpi_comm().Create_group(new_group)
Expand All @@ -501,6 +516,7 @@ def tp_comm(self):
@property
def pp_comm(self):
if self._pp_comm is None:
self._validate_world_size()
mapping = self.mapping
new_group = mpi_comm().group.Incl(mapping.pp_group)
self._pp_comm = mpi_comm().Create_group(new_group)
Expand All @@ -509,6 +525,7 @@ def pp_comm(self):
@property
def cp_comm(self):
if self._cp_comm is None:
self._validate_world_size()
new_group = mpi_comm().group.Incl(self.mapping.cp_group)
self._cp_comm = mpi_comm().Create_group(new_group)
return self._cp_comm
Expand Down