vllm - 💡(How to fix) Fix [Bug][flashinfer 0.6.8]: worker hang on Qwen3.5-397B-A17B-NVFP4 EP=8 (B200 SM100) - bisected to flashinfer-python 0.6.7 → 0.6.8.post1

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Running the standard vllm bench serve against the vllm serve of Qwen3.5-397B-A17B-NVFP4 with data parallelism + expert parallelism on 8× B200 hangs the workers a few hundred requests into the bench. The engine eventually times out on its IPC dequeue and turns into a EngineDeadError.

Bisect (vLLM-side, between adjacent first-parent commits) isolates the regression to PR vllm-project/vllm#39959 "Update flashinfer to 0.6.8", and within that PR to the flashinfer-python 0.6.7 → 0.6.8.post1 version pin in requirements/cuda.txt. Pinning flashinfer back to 0.6.7 on the first-bad vLLM commit restores 1024/1024 PASS.

Update. flashinfer v0.6.11 doesn't fix the bug.

Error Message

File "vllm/v1/executor/multiproc_executor.py", line 386, in get_response status, result = mq.dequeue(timeout=dequeue_timeout) File "vllm/distributed/device_communicators/shm_broadcast.py", line 631, in timeout_ms raise TimeoutError TimeoutError

The above exception was the direct cause of the following exception:

(EngineCore_DPx) ERROR ... [core.py:1138] EngineCore encountered a fatal error. vllm.v1.engine.exceptions.EngineDeadError: EngineCore encountered an issue.

Root Cause

Running the standard vllm bench serve against the vllm serve of Qwen3.5-397B-A17B-NVFP4 with data parallelism + expert parallelism on 8× B200 hangs the workers a few hundred requests into the bench. The engine eventually times out on its IPC dequeue and turns into a EngineDeadError.

Bisect (vLLM-side, between adjacent first-parent commits) isolates the regression to PR vllm-project/vllm#39959 "Update flashinfer to 0.6.8", and within that PR to the flashinfer-python 0.6.7 → 0.6.8.post1 version pin in requirements/cuda.txt. Pinning flashinfer back to 0.6.7 on the first-bad vLLM commit restores 1024/1024 PASS.

Update. flashinfer v0.6.11 doesn't fix the bug.

Fix Action

Fix / Workaround

============================== CPU Info

Architecture: x86_64 CPU op-mode(s): 32-bit, 64-bit Address sizes: 52 bits physical, 57 bits virtual Byte Order: Little Endian CPU(s): 224 On-line CPU(s) list: 0-223 Vendor ID: GenuineIntel Model name: INTEL(R) XEON(R) PLATINUM 8570 CPU family: 6 Model: 207 Thread(s) per core: 2 Core(s) per socket: 56 Socket(s): 2 Stepping: 2 CPU(s) scaling MHz: 29% CPU max MHz: 4000.0000 CPU min MHz: 800.0000 BogoMIPS: 4200.00 Flags: fpu vme de pse tsc msr pae mce cx8 apic sep mtrr pge mca cmov pat pse36 clflush dts acpi mmx fxsr sse sse2 ss ht tm pbe syscall nx pdpe1gb rdtscp lm constant_tsc art arch_perfmon pebs bts rep_good nopl xtopology nonstop_tsc cpuid aperfmperf tsc_known_freq pni pclmulqdq dtes64 monitor ds_cpl vmx smx est tm2 ssse3 sdbg fma cx16 xtpr pdcm pcid dca sse4_1 sse4_2 x2apic movbe popcnt tsc_deadline_timer aes xsave avx f16c rdrand lahf_lm abm 3dnowprefetch cpuid_fault epb cat_l3 cat_l2 cdp_l3 intel_ppin cdp_l2 ssbd mba ibrs ibpb stibp ibrs_enhanced tpr_shadow flexpriority ept vpid ept_ad fsgsbase tsc_adjust bmi1 avx2 smep bmi2 erms invpcid cqm rdt_a avx512f avx512dq rdseed adx smap avx512ifma clflushopt clwb intel_pt avx512cd sha_ni avx512bw avx512vl xsaveopt xsavec xgetbv1 xsaves cqm_llc cqm_occup_llc cqm_mbm_total cqm_mbm_local split_lock_detect user_shstk avx_vnni avx512_bf16 wbnoinvd dtherm ida arat pln pts hwp hwp_act_window hwp_epp hwp_pkg_req vnmi avx512vbmi umip pku ospke waitpkg avx512_vbmi2 gfni vaes vpclmulqdq avx512_vnni avx512_bitalg tme avx512_vpopcntdq la57 rdpid bus_lock_detect cldemote movdiri movdir64b enqcmd fsrm md_clear serialize tsxldtrk pconfig arch_lbr ibt amx_bf16 avx512_fp16 amx_tile amx_int8 flush_l1d arch_capabilities ibpb_exit_to_user Virtualization: VT-x L1d cache: 5.3 MiB (112 instances) L1i cache: 3.5 MiB (112 instances) L2 cache: 224 MiB (112 instances) L3 cache: 600 MiB (2 instances) NUMA node(s): 2 NUMA node0 CPU(s): 0-55,112-167 NUMA node1 CPU(s): 56-111,168-223 Vulnerability Gather data sampling: Not affected Vulnerability Itlb multihit: Not affected Vulnerability L1tf: Not affected Vulnerability Mds: Not affected Vulnerability Meltdown: Not affected Vulnerability Mmio stale data: Not affected Vulnerability Reg file data sampling: Not affected Vulnerability Retbleed: Not affected Vulnerability Spec rstack overflow: Not affected Vulnerability Spec store bypass: Mitigation; Speculative Store Bypass disabled via prctl Vulnerability Spectre v1: Mitigation; usercopy/swapgs barriers and __user pointer sanitization Vulnerability Spectre v2: Mitigation; Enhanced / Automatic IBRS; IBPB conditional; RSB filling; PBRSB-eIBRS SW sequence; BHI BHI_DIS_S Vulnerability Srbds: Not affected Vulnerability Tsx async abort: Not affected Vulnerability Vmscape: Mitigation; IBPB before exit to userspace

Code Example

Collecting environment information...
uv is set
==============================
        System Info
==============================
OS                           : Ubuntu 24.04.4 LTS (x86_64)
GCC version                  : (Ubuntu 13.3.0-6ubuntu2~24.04.1) 13.3.0
Clang version                : Could not collect
CMake version                : version 3.28.3
Libc version                 : glibc-2.39

==============================
       PyTorch Info
==============================
PyTorch version              : 2.11.0+cu130
Is debug build               : False
CUDA used to build PyTorch   : 13.0
ROCM used to build PyTorch   : N/A
XPU used to build PyTorch    : N/A

==============================
      Python Environment
==============================
Python version               : 3.12.12 (main, Oct 14 2025, 21:25:31) [Clang 20.1.4 ] (64-bit runtime)
Python platform              : Linux-6.8.0-90-generic-x86_64-with-glibc2.39
    
==============================
       CUDA / GPU Info
==============================
Is CUDA available            : True
CUDA runtime version         : 13.0.48
CUDA_MODULE_LOADING set to   : 
GPU models and configuration : 
GPU 0: NVIDIA B200
GPU 1: NVIDIA B200
GPU 2: NVIDIA B200
GPU 3: NVIDIA B200
GPU 4: NVIDIA B200
GPU 5: NVIDIA B200
GPU 6: NVIDIA B200
GPU 7: NVIDIA B200

Nvidia driver version        : 595.58.03
cuDNN version                : Could not collect
HIP runtime version          : N/A
MIOpen runtime version       : N/A
Is XNNPACK available         : True

==============================
          CPU Info
==============================
Architecture:                         x86_64
CPU op-mode(s):                       32-bit, 64-bit
Address sizes:                        52 bits physical, 57 bits virtual
Byte Order:                           Little Endian
CPU(s):                               224
On-line CPU(s) list:                  0-223
Vendor ID:                            GenuineIntel
Model name:                           INTEL(R) XEON(R) PLATINUM 8570
CPU family:                           6
Model:                                207
Thread(s) per core:                   2
Core(s) per socket:                   56
Socket(s):                            2
Stepping:                             2
CPU(s) scaling MHz:                   29%
CPU max MHz:                          4000.0000
CPU min MHz:                          800.0000
BogoMIPS:                             4200.00
Flags:                                fpu vme de pse tsc msr pae mce cx8 apic sep mtrr pge mca cmov pat pse36 clflush dts acpi mmx fxsr sse sse2 ss ht tm pbe syscall nx pdpe1gb rdtscp lm constant_tsc art arch_perfmon pebs bts rep_good nopl xtopology nonstop_tsc cpuid aperfmperf tsc_known_freq pni pclmulqdq dtes64 monitor ds_cpl vmx smx est tm2 ssse3 sdbg fma cx16 xtpr pdcm pcid dca sse4_1 sse4_2 x2apic movbe popcnt tsc_deadline_timer aes xsave avx f16c rdrand lahf_lm abm 3dnowprefetch cpuid_fault epb cat_l3 cat_l2 cdp_l3 intel_ppin cdp_l2 ssbd mba ibrs ibpb stibp ibrs_enhanced tpr_shadow flexpriority ept vpid ept_ad fsgsbase tsc_adjust bmi1 avx2 smep bmi2 erms invpcid cqm rdt_a avx512f avx512dq rdseed adx smap avx512ifma clflushopt clwb intel_pt avx512cd sha_ni avx512bw avx512vl xsaveopt xsavec xgetbv1 xsaves cqm_llc cqm_occup_llc cqm_mbm_total cqm_mbm_local split_lock_detect user_shstk avx_vnni avx512_bf16 wbnoinvd dtherm ida arat pln pts hwp hwp_act_window hwp_epp hwp_pkg_req vnmi avx512vbmi umip pku ospke waitpkg avx512_vbmi2 gfni vaes vpclmulqdq avx512_vnni avx512_bitalg tme avx512_vpopcntdq la57 rdpid bus_lock_detect cldemote movdiri movdir64b enqcmd fsrm md_clear serialize tsxldtrk pconfig arch_lbr ibt amx_bf16 avx512_fp16 amx_tile amx_int8 flush_l1d arch_capabilities ibpb_exit_to_user
Virtualization:                       VT-x
L1d cache:                            5.3 MiB (112 instances)
L1i cache:                            3.5 MiB (112 instances)
L2 cache:                             224 MiB (112 instances)
L3 cache:                             600 MiB (2 instances)
NUMA node(s):                         2
NUMA node0 CPU(s):                    0-55,112-167
NUMA node1 CPU(s):                    56-111,168-223
Vulnerability Gather data sampling:   Not affected
Vulnerability Itlb multihit:          Not affected
Vulnerability L1tf:                   Not affected
Vulnerability Mds:                    Not affected
Vulnerability Meltdown:               Not affected
Vulnerability Mmio stale data:        Not affected
Vulnerability Reg file data sampling: Not affected
Vulnerability Retbleed:               Not affected
Vulnerability Spec rstack overflow:   Not affected
Vulnerability Spec store bypass:      Mitigation; Speculative Store Bypass disabled via prctl
Vulnerability Spectre v1:             Mitigation; usercopy/swapgs barriers and __user pointer sanitization
Vulnerability Spectre v2:             Mitigation; Enhanced / Automatic IBRS; IBPB conditional; RSB filling; PBRSB-eIBRS SW sequence; BHI BHI_DIS_S
Vulnerability Srbds:                  Not affected
Vulnerability Tsx async abort:        Not affected
Vulnerability Vmscape:                Mitigation; IBPB before exit to userspace

==============================
Versions of relevant libraries
==============================
[pip3] flashinfer-python==0.6.8.post1
[pip3] numpy==2.2.6
[pip3] nvidia-cublas==13.1.0.3
[pip3] nvidia-cublas-cu12==12.9.1.4
[pip3] nvidia-cuda-cupti==13.0.85
[pip3] nvidia-cuda-cupti-cu12==12.9.79
[pip3] nvidia-cuda-nvrtc==13.0.88
[pip3] nvidia-cuda-nvrtc-cu12==12.9.86
[pip3] nvidia-cuda-runtime==13.0.96
[pip3] nvidia-cuda-runtime-cu12==12.9.79
[pip3] nvidia-cudnn-cu12==9.10.2.21
[pip3] nvidia-cudnn-cu13==9.19.0.56
[pip3] nvidia-cudnn-frontend==1.18.0
[pip3] nvidia-cufft==12.0.0.61
[pip3] nvidia-cufft-cu12==11.4.1.4
[pip3] nvidia-cufile==1.15.1.6
[pip3] nvidia-cufile-cu12==1.14.1.1
[pip3] nvidia-curand==10.4.0.35
[pip3] nvidia-curand-cu12==10.3.10.19
[pip3] nvidia-cusolver==12.0.4.66
[pip3] nvidia-cusolver-cu12==11.7.5.82
[pip3] nvidia-cusparse==12.6.3.3
[pip3] nvidia-cusparse-cu12==12.5.10.65
[pip3] nvidia-cusparselt-cu12==0.7.1
[pip3] nvidia-cusparselt-cu13==0.8.0
[pip3] nvidia-cutlass-dsl==4.4.2
[pip3] nvidia-cutlass-dsl-libs-base==4.4.2
[pip3] nvidia-ml-py==13.590.48
[pip3] nvidia-nccl-cu12==2.27.5
[pip3] nvidia-nccl-cu13==2.28.9
[pip3] nvidia-nvjitlink==13.0.88
[pip3] nvidia-nvjitlink-cu12==12.9.86
[pip3] nvidia-nvshmem-cu12==3.4.5
[pip3] nvidia-nvshmem-cu13==3.4.5
[pip3] nvidia-nvtx==13.0.85
[pip3] nvidia-nvtx-cu12==12.9.79
[pip3] pyzmq==27.1.0
[pip3] torch==2.11.0+cu130
[pip3] torch-c-dlpack-ext==0.1.5
[pip3] torchaudio==2.11.0+cu130
[pip3] torchvision==0.26.0+cu130
[pip3] transformers==4.57.6
[pip3] triton==3.6.0
[conda] Could not collect

==============================
         vLLM Info
==============================
ROCM Version                 : Could not collect
vLLM Version                 : 0.19.2rc1.dev47+g191e3fdaa (git sha: 191e3fdaa)
vLLM Build Flags:
  CUDA Archs: Not Set; ROCm: Disabled; XPU: Disabled
GPU Topology:
  	GPU0	GPU1	GPU2	GPU3	GPU4	GPU5	GPU6	GPU7	NIC0	NIC1	NIC2	NIC3	NIC4	NIC5	NIC6	NIC7	NIC8	NIC9	NIC10	NIC11	NIC12	NIC13	NIC14	NIC15	CPU Affinity	NUMA Affinity	GPU NUMA ID
GPU0	 X 	NV18	NV18	NV18	NV18	NV18	NV18	NV18	NODE	NODE	NODE	NODE	PXB	NODE	NODE	NODE	NODE	NODE	SYS	SYS	SYS	SYS	SYS	SYS	0-55,112-167	0		N/A
GPU1	NV18	 X 	NV18	NV18	NV18	NV18	NV18	NV18	NODE	NODE	NODE	NODE	NODE	NODE	NODE	PXB	NODE	NODE	SYS	SYS	SYS	SYS	SYS	SYS	0-55,112-167	0		N/A
GPU2	NV18	NV18	 X 	NV18	NV18	NV18	NV18	NV18	NODE	NODE	NODE	NODE	NODE	NODE	NODE	NODE	PXB	NODE	SYS	SYS	SYS	SYS	SYS	SYS	0-55,112-167	0		N/A
GPU3	NV18	NV18	NV18	 X 	NV18	NV18	NV18	NV18	NODE	NODE	NODE	NODE	NODE	NODE	NODE	NODE	NODE	PXB	SYS	SYS	SYS	SYS	SYS	SYS	0-55,112-167	0		N/A
GPU4	NV18	NV18	NV18	NV18	 X 	NV18	NV18	NV18	SYS	SYS	SYS	SYS	SYS	SYS	SYS	SYS	SYS	SYS	PXB	NODE	NODE	NODE	NODE	NODE	56-111,168-223	1		N/A
GPU5	NV18	NV18	NV18	NV18	NV18	 X 	NV18	NV18	SYS	SYS	SYS	SYS	SYS	SYS	SYS	SYS	SYS	SYS	NODE	NODE	NODE	PXB	NODE	NODE	56-111,168-223	1		N/A
GPU6	NV18	NV18	NV18	NV18	NV18	NV18	 X 	NV18	SYS	SYS	SYS	SYS	SYS	SYS	SYS	SYS	SYS	SYS	NODE	NODE	NODE	NODE	PXB	NODE	56-111,168-223	1		N/A
GPU7	NV18	NV18	NV18	NV18	NV18	NV18	NV18	 X 	SYS	SYS	SYS	SYS	SYS	SYS	SYS	SYS	SYS	SYS	NODE	NODE	NODE	NODE	NODE	PXB	56-111,168-223	1		N/A
NIC0	NODE	NODE	NODE	NODE	SYS	SYS	SYS	SYS	 X 	PIX	PIX	PIX	NODE	NODE	NODE	NODE	NODE	NODE	SYS	SYS	SYS	SYS	SYS	SYS				
NIC1	NODE	NODE	NODE	NODE	SYS	SYS	SYS	SYS	PIX	 X 	PIX	PIX	NODE	NODE	NODE	NODE	NODE	NODE	SYS	SYS	SYS	SYS	SYS	SYS				
NIC2	NODE	NODE	NODE	NODE	SYS	SYS	SYS	SYS	PIX	PIX	 X 	PIX	NODE	NODE	NODE	NODE	NODE	NODE	SYS	SYS	SYS	SYS	SYS	SYS				
NIC3	NODE	NODE	NODE	NODE	SYS	SYS	SYS	SYS	PIX	PIX	PIX	 X 	NODE	NODE	NODE	NODE	NODE	NODE	SYS	SYS	SYS	SYS	SYS	SYS				
NIC4	PXB	NODE	NODE	NODE	SYS	SYS	SYS	SYS	NODE	NODE	NODE	NODE	 X 	NODE	NODE	NODE	NODE	NODE	SYS	SYS	SYS	SYS	SYS	SYS				
NIC5	NODE	NODE	NODE	NODE	SYS	SYS	SYS	SYS	NODE	NODE	NODE	NODE	NODE	 X 	PIX	NODE	NODE	NODE	SYS	SYS	SYS	SYS	SYS	SYS				
NIC6	NODE	NODE	NODE	NODE	SYS	SYS	SYS	SYS	NODE	NODE	NODE	NODE	NODE	PIX	 X 	NODE	NODE	NODE	SYS	SYS	SYS	SYS	SYS	SYS				
NIC7	NODE	PXB	NODE	NODE	SYS	SYS	SYS	SYS	NODE	NODE	NODE	NODE	NODE	NODE	NODE	 X 	NODE	NODE	SYS	SYS	SYS	SYS	SYS	SYS				
NIC8	NODE	NODE	PXB	NODE	SYS	SYS	SYS	SYS	NODE	NODE	NODE	NODE	NODE	NODE	NODE	NODE	 X 	NODE	SYS	SYS	SYS	SYS	SYS	SYS				
NIC9	NODE	NODE	NODE	PXB	SYS	SYS	SYS	SYS	NODE	NODE	NODE	NODE	NODE	NODE	NODE	NODE	NODE	 X 	SYS	SYS	SYS	SYS	SYS	SYS				
NIC10	SYS	SYS	SYS	SYS	PXB	NODE	NODE	NODE	SYS	SYS	SYS	SYS	SYS	SYS	SYS	SYS	SYS	SYS	 X 	NODE	NODE	NODE	NODE	NODE				
NIC11	SYS	SYS	SYS	SYS	NODE	NODE	NODE	NODE	SYS	SYS	SYS	SYS	SYS	SYS	SYS	SYS	SYS	SYS	NODE	 X 	PIX	NODE	NODE	NODE				
NIC12	SYS	SYS	SYS	SYS	NODE	NODE	NODE	NODE	SYS	SYS	SYS	SYS	SYS	SYS	SYS	SYS	SYS	SYS	NODE	PIX	 X 	NODE	NODE	NODE				
NIC13	SYS	SYS	SYS	SYS	NODE	PXB	NODE	NODE	SYS	SYS	SYS	SYS	SYS	SYS	SYS	SYS	SYS	SYS	NODE	NODE	NODE	 X 	NODE	NODE				
NIC14	SYS	SYS	SYS	SYS	NODE	NODE	PXB	NODE	SYS	SYS	SYS	SYS	SYS	SYS	SYS	SYS	SYS	SYS	NODE	NODE	NODE	NODE	 X 	NODE				
NIC15	SYS	SYS	SYS	SYS	NODE	NODE	NODE	PXB	SYS	SYS	SYS	SYS	SYS	SYS	SYS	SYS	SYS	SYS	NODE	NODE	NODE	NODE	NODE	 X 				

Legend:

  X    = Self
  SYS  = Connection traversing PCIe as well as the SMP interconnect between NUMA nodes (e.g., QPI/UPI)
  NODE = Connection traversing PCIe as well as the interconnect between PCIe Host Bridges within a NUMA node
  PHB  = Connection traversing PCIe as well as a PCIe Host Bridge (typically the CPU)
  PXB  = Connection traversing multiple PCIe bridges (without traversing the PCIe Host Bridge)
  PIX  = Connection traversing at most a single PCIe bridge
  NV#  = Connection traversing a bonded set of # NVLinks

NIC Legend:

  NIC0: mlx5_0
  NIC1: mlx5_1
  NIC2: mlx5_2
  NIC3: mlx5_3
  NIC4: mlx5_4
  NIC5: mlx5_5
  NIC6: mlx5_6
  NIC7: mlx5_7
  NIC8: mlx5_8
  NIC9: mlx5_9
  NIC10: mlx5_10
  NIC11: mlx5_11
  NIC12: mlx5_12
  NIC13: mlx5_13
  NIC14: mlx5_14
  NIC15: mlx5_15

==============================
     Environment Variables
==============================
NVIDIA_VISIBLE_DEVICES=GPU-8317f78c-f99d-83bd-c482-32dac10ef30c,GPU-8fc7a7b6-bcef-c33d-4892-d0fede2d5f0f,GPU-b37834f6-e251-1183-1917-a2e8b43b9fc4,GPU-13fa1039-be1e-010e-413e-36eec85e98f8,GPU-d878248b-2c48-d6bc-373f-f4fa503999bf,GPU-73ea9b4f-1089-1e83-fbe5-1e20e9021147,GPU-12f455bd-4fb9-9ac5-d065-962815ef9675,GPU-d34404df-593a-d600-db7e-7b4b3bbeec38
CUDA_MPS_PIPE_DIRECTORY=/tmp/nvidia-mps/job-2100478
CUDA_VISIBLE_DEVICES=0,1,2,3,4,5,6,7
CUDA_VISIBLE_DEVICES=0,1,2,3,4,5,6,7
CUDA_MPS_LOG_DIRECTORY=/tmp/nvidia-mps/job-2100478/logs
LD_LIBRARY_PATH=/home/scratch.vgimpelson_ent/cuda/cuda130/lib64:
CUDA_HOME=/home/scratch.vgimpelson_ent/cuda/cuda130
CUDA_HOME=/home/scratch.vgimpelson_ent/cuda/cuda130
PYTORCH_NVML_BASED_CUDA_CHECK=1
TORCHINDUCTOR_COMPILE_THREADS=1
TORCHINDUCTOR_CACHE_DIR=/tmp/vgimpelson/torchinductor_vgimpelson

---

==============================
        System Info
==============================
OS                           : Ubuntu 24.04.4 LTS (x86_64)
GCC version                  : (Ubuntu 13.3.0-6ubuntu2~24.04.1) 13.3.0
Clang version                : Could not collect
CMake version                : Could not collect
Libc version                 : glibc-2.39

==============================
       PyTorch Info
==============================
PyTorch version              : 2.11.0+cu130
Is debug build               : False
CUDA used to build PyTorch   : 13.0
ROCM used to build PyTorch   : N/A
XPU used to build PyTorch    : N/A

==============================
      Python Environment
==============================
Python version               : 3.12.3 (main, Jan 22 2026, 20:57:42) [GCC 13.3.0] (64-bit runtime)
Python platform              : Linux-6.14.0-37-generic-x86_64-with-glibc2.39

==============================
       CUDA / GPU Info
==============================
Is CUDA available            : True
CUDA runtime version         : 12.8.61
CUDA_MODULE_LOADING set to   :
GPU models and configuration :
GPU 0: NVIDIA B200
GPU 1: NVIDIA B200
GPU 2: NVIDIA B200
GPU 3: NVIDIA B200
GPU 4: NVIDIA B200
GPU 5: NVIDIA B200
GPU 6: NVIDIA B200
GPU 7: NVIDIA B200

Nvidia driver version        : 580.126.09
cuDNN version                : Could not collect
HIP runtime version          : N/A
MIOpen runtime version       : N/A
Is XNNPACK available         : True

==============================
          CPU Info
==============================
Architecture:                            x86_64
CPU op-mode(s):                          32-bit, 64-bit
Address sizes:                           52 bits physical, 57 bits virtual
Byte Order:                              Little Endian
CPU(s):                                  224
On-line CPU(s) list:                     0-223
Vendor ID:                               GenuineIntel
Model name:                              INTEL(R) XEON(R) PLATINUM 8570
CPU family:                              6
Model:                                   207
Thread(s) per core:                      2
Core(s) per socket:                      56
Socket(s):                               2
Stepping:                                2
CPU(s) scaling MHz:                      49%
CPU max MHz:                             4000.0000
CPU min MHz:                             800.0000
BogoMIPS:                                4200.00
Flags:                                   fpu vme de pse tsc msr pae mce cx8 apic sep mtrr pge mca cmov pat pse36 clflush dts acpi mmx fxsr sse sse2 ss ht tm pbe syscall nx pdpe1gb rdtscp lm constant_tsc art arch_perfmon pebs bts rep_good nopl xtopology nonstop_tsc cpuid aperfmperf tsc_known_freq pni pclmulqdq dtes64 monitor ds_cpl vmx smx est tm2 ssse3 sdbg fma cx16 xtpr pdcm pcid dca sse4_1 sse4_2 x2apic movbe popcnt tsc_deadline_timer aes xsave avx f16c rdrand lahf_lm abm 3dnowprefetch cpuid_fault epb cat_l3 cat_l2 cdp_l3 intel_ppin cdp_l2 ssbd mba ibrs ibpb stibp ibrs_enhanced tpr_shadow flexpriority ept vpid ept_ad fsgsbase tsc_adjust bmi1 avx2 smep bmi2 erms invpcid cqm rdt_a avx512f avx512dq rdseed adx smap avx512ifma clflushopt clwb intel_pt avx512cd sha_ni avx512bw avx512vl xsaveopt xsavec xgetbv1 xsaves cqm_llc cqm_occup_llc cqm_mbm_total cqm_mbm_local split_lock_detect user_shstk avx_vnni avx512_bf16 wbnoinvd dtherm ida arat pln pts hwp hwp_act_window hwp_epp hwp_pkg_req vnmi avx512vbmi umip pku ospke waitpkg avx512_vbmi2 gfni vaes vpclmulqdq avx512_vnni avx512_bitalg avx512_vpopcntdq la57 rdpid bus_lock_detect cldemote movdiri movdir64b enqcmd fsrm md_clear serialize tsxldtrk pconfig arch_lbr ibt amx_bf16 avx512_fp16 amx_tile amx_int8 flush_l1d arch_capabilities
Virtualization:                          VT-x
L1d cache:                               5.3 MiB (112 instances)
L1i cache:                               3.5 MiB (112 instances)
L2 cache:                                224 MiB (112 instances)
L3 cache:                                600 MiB (2 instances)
NUMA node(s):                            2
NUMA node0 CPU(s):                       0-55,112-167
NUMA node1 CPU(s):                       56-111,168-223
Vulnerability Gather data sampling:      Not affected
Vulnerability Ghostwrite:                Not affected
Vulnerability Indirect target selection: Not affected
Vulnerability Itlb multihit:             Not affected
Vulnerability L1tf:                      Not affected
Vulnerability Mds:                       Not affected
Vulnerability Meltdown:                  Not affected
Vulnerability Mmio stale data:           Not affected
Vulnerability Reg file data sampling:    Not affected
Vulnerability Retbleed:                  Not affected
Vulnerability Spec rstack overflow:      Not affected
Vulnerability Spec store bypass:         Vulnerable
Vulnerability Spectre v1:                Vulnerable: __user pointer sanitization and usercopy barriers only; no swapgs barriers
Vulnerability Spectre v2:                Vulnerable; IBPB: disabled; STIBP: disabled; PBRSB-eIBRS: Vulnerable; BHI: Vulnerable
Vulnerability Srbds:                     Not affected
Vulnerability Tsa:                       Not affected
Vulnerability Tsx async abort:           Not affected
Vulnerability Vmscape:                   Vulnerable

==============================
Versions of relevant libraries
==============================
[pip3] flashinfer-python==0.6.8.post1
[pip3] numpy==2.2.6
[pip3] nvidia-cublas==13.1.0.3
[pip3] nvidia-cuda-cupti==13.0.85
[pip3] nvidia-cuda-nvrtc==13.0.88
[pip3] nvidia-cuda-runtime==13.0.96
[pip3] nvidia-cudnn-cu13==9.19.0.56
[pip3] nvidia-cudnn-frontend==1.18.0
[pip3] nvidia-cufft==12.0.0.61
[pip3] nvidia-cufile==1.15.1.6
[pip3] nvidia-curand==10.4.0.35
[pip3] nvidia-cusolver==12.0.4.66
[pip3] nvidia-cusparse==12.6.3.3
[pip3] nvidia-cusparselt-cu13==0.8.0
[pip3] nvidia-cutlass-dsl==4.5.0
[pip3] nvidia-cutlass-dsl-libs-base==4.5.0
[pip3] nvidia-ml-py==13.595.45
[pip3] nvidia-nccl-cu13==2.28.9
[pip3] nvidia-nvjitlink==13.0.88
[pip3] nvidia-nvshmem-cu13==3.4.5
[pip3] nvidia-nvtx==13.0.85
[pip3] pyzmq==27.1.0
[pip3] torch==2.11.0+cu130
[pip3] torch_c_dlpack_ext==0.1.5
[pip3] torchaudio==2.11.0+cu130
[pip3] torchvision==0.26.0+cu130
[pip3] transformers==5.8.0
[pip3] triton==3.6.0
[conda] Could not collect

==============================
         vLLM Info
==============================
ROCM Version                 : Could not collect
vLLM Version                 : 0.19.2rc1.dev47+g191e3fdaa (git sha: 191e3fdaa)
vLLM Build Flags:
  CUDA Archs: Not Set; ROCm: Disabled; XPU: Disabled
GPU Topology:
        GPU0    GPU1    GPU2    GPU3    GPU4    GPU5    GPU6    GPU7    NIC0    NIC1    NIC2    NIC3    NIC4    NIC5    NIC6   NIC7     NIC8    NIC9    NIC10   NIC11   NIC12   NIC13   NIC14   NIC15   CPU Affinity    NUMA Affinity   GPU NUMA ID
GPU0     X      NV18    NV18    NV18    NV18    NV18    NV18    NV18    NODE    NODE    NODE    NODE    PXB     NODE    NODE   NODE     NODE    NODE    SYS     SYS     SYS     SYS     SYS     SYS     0-55,112-167    0               N/A
GPU1    NV18     X      NV18    NV18    NV18    NV18    NV18    NV18    NODE    NODE    NODE    NODE    NODE    NODE    NODE   PXB      NODE    NODE    SYS     SYS     SYS     SYS     SYS     SYS     0-55,112-167    0               N/A
GPU2    NV18    NV18     X      NV18    NV18    NV18    NV18    NV18    NODE    NODE    NODE    NODE    NODE    NODE    NODE   NODE     PXB     NODE    SYS     SYS     SYS     SYS     SYS     SYS     0-55,112-167    0               N/A
GPU3    NV18    NV18    NV18     X      NV18    NV18    NV18    NV18    NODE    NODE    NODE    NODE    NODE    NODE    NODE   NODE     NODE    PXB     SYS     SYS     SYS     SYS     SYS     SYS     0-55,112-167    0               N/A
GPU4    NV18    NV18    NV18    NV18     X      NV18    NV18    NV18    SYS     SYS     SYS     SYS     SYS     SYS     SYS    SYS      SYS     SYS     PXB     NODE    NODE    NODE    NODE    NODE    56-111,168-223  1               N/A
GPU5    NV18    NV18    NV18    NV18    NV18     X      NV18    NV18    SYS     SYS     SYS     SYS     SYS     SYS     SYS    SYS      SYS     SYS     NODE    NODE    NODE    PXB     NODE    NODE    56-111,168-223  1               N/A
GPU6    NV18    NV18    NV18    NV18    NV18    NV18     X      NV18    SYS     SYS     SYS     SYS     SYS     SYS     SYS    SYS      SYS     SYS     NODE    NODE    NODE    NODE    PXB     NODE    56-111,168-223  1               N/A
GPU7    NV18    NV18    NV18    NV18    NV18    NV18    NV18     X      SYS     SYS     SYS     SYS     SYS     SYS     SYS    SYS      SYS     SYS     NODE    NODE    NODE    NODE    NODE    PXB     56-111,168-223  1               N/A
NIC0    NODE    NODE    NODE    NODE    SYS     SYS     SYS     SYS      X      PIX     PIX     PIX     NODE    NODE    NODE   NODE     NODE    NODE    SYS     SYS     SYS     SYS     SYS     SYS
NIC1    NODE    NODE    NODE    NODE    SYS     SYS     SYS     SYS     PIX      X      PIX     PIX     NODE    NODE    NODE   NODE     NODE    NODE    SYS     SYS     SYS     SYS     SYS     SYS
NIC2    NODE    NODE    NODE    NODE    SYS     SYS     SYS     SYS     PIX     PIX      X      PIX     NODE    NODE    NODE   NODE     NODE    NODE    SYS     SYS     SYS     SYS     SYS     SYS
NIC3    NODE    NODE    NODE    NODE    SYS     SYS     SYS     SYS     PIX     PIX     PIX      X      NODE    NODE    NODE   NODE     NODE    NODE    SYS     SYS     SYS     SYS     SYS     SYS
NIC4    PXB     NODE    NODE    NODE    SYS     SYS     SYS     SYS     NODE    NODE    NODE    NODE     X      NODE    NODE   NODE     NODE    NODE    SYS     SYS     SYS     SYS     SYS     SYS
NIC5    NODE    NODE    NODE    NODE    SYS     SYS     SYS     SYS     NODE    NODE    NODE    NODE    NODE     X      PIX    NODE     NODE    NODE    SYS     SYS     SYS     SYS     SYS     SYS
NIC6    NODE    NODE    NODE    NODE    SYS     SYS     SYS     SYS     NODE    NODE    NODE    NODE    NODE    PIX      X     NODE     NODE    NODE    SYS     SYS     SYS     SYS     SYS     SYS
NIC7    NODE    PXB     NODE    NODE    SYS     SYS     SYS     SYS     NODE    NODE    NODE    NODE    NODE    NODE    NODE    X       NODE    NODE    SYS     SYS     SYS     SYS     SYS     SYS
NIC8    NODE    NODE    PXB     NODE    SYS     SYS     SYS     SYS     NODE    NODE    NODE    NODE    NODE    NODE    NODE   NODE      X      NODE    SYS     SYS     SYS     SYS     SYS     SYS
NIC9    NODE    NODE    NODE    PXB     SYS     SYS     SYS     SYS     NODE    NODE    NODE    NODE    NODE    NODE    NODE   NODE     NODE     X      SYS     SYS     SYS     SYS     SYS     SYS
NIC10   SYS     SYS     SYS     SYS     PXB     NODE    NODE    NODE    SYS     SYS     SYS     SYS     SYS     SYS     SYS    SYS      SYS     SYS      X      NODE    NODE    NODE    NODE    NODE
NIC11   SYS     SYS     SYS     SYS     NODE    NODE    NODE    NODE    SYS     SYS     SYS     SYS     SYS     SYS     SYS    SYS      SYS     SYS     NODE     X      PIX     NODE    NODE    NODE
NIC12   SYS     SYS     SYS     SYS     NODE    NODE    NODE    NODE    SYS     SYS     SYS     SYS     SYS     SYS     SYS    SYS      SYS     SYS     NODE    PIX      X      NODE    NODE    NODE
NIC13   SYS     SYS     SYS     SYS     NODE    PXB     NODE    NODE    SYS     SYS     SYS     SYS     SYS     SYS     SYS    SYS      SYS     SYS     NODE    NODE    NODE     X      NODE    NODE
NIC14   SYS     SYS     SYS     SYS     NODE    NODE    PXB     NODE    SYS     SYS     SYS     SYS     SYS     SYS     SYS    SYS      SYS     SYS     NODE    NODE    NODE    NODE     X      NODE
NIC15   SYS     SYS     SYS     SYS     NODE    NODE    NODE    PXB     SYS     SYS     SYS     SYS     SYS     SYS     SYS    SYS      SYS     SYS     NODE    NODE    NODE    NODE    NODE     X

Legend:

  X    = Self
  SYS  = Connection traversing PCIe as well as the SMP interconnect between NUMA nodes (e.g., QPI/UPI)
  NODE = Connection traversing PCIe as well as the interconnect between PCIe Host Bridges within a NUMA node
  PHB  = Connection traversing PCIe as well as a PCIe Host Bridge (typically the CPU)
  PXB  = Connection traversing multiple PCIe bridges (without traversing the PCIe Host Bridge)
  PIX  = Connection traversing at most a single PCIe bridge
  NV#  = Connection traversing a bonded set of # NVLinks

NIC Legend:

  NIC0: mlx5_0
  NIC1: mlx5_1
  NIC2: mlx5_2
  NIC3: mlx5_3
  NIC4: mlx5_4
  NIC5: mlx5_5
  NIC6: mlx5_6
  NIC7: mlx5_7
  NIC8: mlx5_8
  NIC9: mlx5_9
  NIC10: mlx5_10
  NIC11: mlx5_11
  NIC12: mlx5_12
  NIC13: mlx5_13
  NIC14: mlx5_14
  NIC15: mlx5_15

==============================
     Environment Variables
==============================
LD_LIBRARY_PATH=/home/aperevedents/storage/cuda/cuda128/lib64:
CUDA_HOME=/home/aperevedents/storage/cuda/cuda128
CUDA_HOME=/home/aperevedents/storage/cuda/cuda128
PYTORCH_NVML_BASED_CUDA_CHECK=1
TORCHINDUCTOR_COMPILE_THREADS=1
TORCHINDUCTOR_CACHE_DIR=/tmp/torchinductor_aperevedents

---

vllm serve nvidia/Qwen3.5-397B-A17B-NVFP4 \
    --port 8000 \
    -tp 1 -pp 1 -dp 8 \
    --enable-expert-parallel \
    --language-model-only \
    --reasoning-parser qwen3 \
    --stream-interval 100

---

vllm bench serve --backend vllm \
    --model nvidia/Qwen3.5-397B-A17B-NVFP4 \
    --port 8000 \
    --endpoint /v1/completions \
    --ignore-eos --temperature 0.0 \
    --dataset-name random --random-input 8192 --random-output 1 \
    --num-prompt 1024 --max-concurrency 128

---

shm_broadcast.py:681 ... No available shared memory broadcast block found in 60 seconds.
This typically happens when some processes are hanging or doing some time-consuming
work (e.g. compilation, weight/kv cache quantization).

---

File "vllm/v1/executor/multiproc_executor.py", line 386, in get_response
    status, result = mq.dequeue(timeout=dequeue_timeout)
File "vllm/distributed/device_communicators/shm_broadcast.py", line 631, in timeout_ms
    raise TimeoutError
TimeoutError

The above exception was the direct cause of the following exception:

(EngineCore_DPx) ERROR ... [core.py:1138] EngineCore encountered a fatal error.
vllm.v1.engine.exceptions.EngineDeadError: EngineCore encountered an issue.
RAW_BUFFERClick to expand / collapse

Your current environment

<details> <summary>The output of <code>python collect_env.py</code></summary>
Collecting environment information...
uv is set
==============================
        System Info
==============================
OS                           : Ubuntu 24.04.4 LTS (x86_64)
GCC version                  : (Ubuntu 13.3.0-6ubuntu2~24.04.1) 13.3.0
Clang version                : Could not collect
CMake version                : version 3.28.3
Libc version                 : glibc-2.39

==============================
       PyTorch Info
==============================
PyTorch version              : 2.11.0+cu130
Is debug build               : False
CUDA used to build PyTorch   : 13.0
ROCM used to build PyTorch   : N/A
XPU used to build PyTorch    : N/A

==============================
      Python Environment
==============================
Python version               : 3.12.12 (main, Oct 14 2025, 21:25:31) [Clang 20.1.4 ] (64-bit runtime)
Python platform              : Linux-6.8.0-90-generic-x86_64-with-glibc2.39
    
==============================
       CUDA / GPU Info
==============================
Is CUDA available            : True
CUDA runtime version         : 13.0.48
CUDA_MODULE_LOADING set to   : 
GPU models and configuration : 
GPU 0: NVIDIA B200
GPU 1: NVIDIA B200
GPU 2: NVIDIA B200
GPU 3: NVIDIA B200
GPU 4: NVIDIA B200
GPU 5: NVIDIA B200
GPU 6: NVIDIA B200
GPU 7: NVIDIA B200

Nvidia driver version        : 595.58.03
cuDNN version                : Could not collect
HIP runtime version          : N/A
MIOpen runtime version       : N/A
Is XNNPACK available         : True

==============================
          CPU Info
==============================
Architecture:                         x86_64
CPU op-mode(s):                       32-bit, 64-bit
Address sizes:                        52 bits physical, 57 bits virtual
Byte Order:                           Little Endian
CPU(s):                               224
On-line CPU(s) list:                  0-223
Vendor ID:                            GenuineIntel
Model name:                           INTEL(R) XEON(R) PLATINUM 8570
CPU family:                           6
Model:                                207
Thread(s) per core:                   2
Core(s) per socket:                   56
Socket(s):                            2
Stepping:                             2
CPU(s) scaling MHz:                   29%
CPU max MHz:                          4000.0000
CPU min MHz:                          800.0000
BogoMIPS:                             4200.00
Flags:                                fpu vme de pse tsc msr pae mce cx8 apic sep mtrr pge mca cmov pat pse36 clflush dts acpi mmx fxsr sse sse2 ss ht tm pbe syscall nx pdpe1gb rdtscp lm constant_tsc art arch_perfmon pebs bts rep_good nopl xtopology nonstop_tsc cpuid aperfmperf tsc_known_freq pni pclmulqdq dtes64 monitor ds_cpl vmx smx est tm2 ssse3 sdbg fma cx16 xtpr pdcm pcid dca sse4_1 sse4_2 x2apic movbe popcnt tsc_deadline_timer aes xsave avx f16c rdrand lahf_lm abm 3dnowprefetch cpuid_fault epb cat_l3 cat_l2 cdp_l3 intel_ppin cdp_l2 ssbd mba ibrs ibpb stibp ibrs_enhanced tpr_shadow flexpriority ept vpid ept_ad fsgsbase tsc_adjust bmi1 avx2 smep bmi2 erms invpcid cqm rdt_a avx512f avx512dq rdseed adx smap avx512ifma clflushopt clwb intel_pt avx512cd sha_ni avx512bw avx512vl xsaveopt xsavec xgetbv1 xsaves cqm_llc cqm_occup_llc cqm_mbm_total cqm_mbm_local split_lock_detect user_shstk avx_vnni avx512_bf16 wbnoinvd dtherm ida arat pln pts hwp hwp_act_window hwp_epp hwp_pkg_req vnmi avx512vbmi umip pku ospke waitpkg avx512_vbmi2 gfni vaes vpclmulqdq avx512_vnni avx512_bitalg tme avx512_vpopcntdq la57 rdpid bus_lock_detect cldemote movdiri movdir64b enqcmd fsrm md_clear serialize tsxldtrk pconfig arch_lbr ibt amx_bf16 avx512_fp16 amx_tile amx_int8 flush_l1d arch_capabilities ibpb_exit_to_user
Virtualization:                       VT-x
L1d cache:                            5.3 MiB (112 instances)
L1i cache:                            3.5 MiB (112 instances)
L2 cache:                             224 MiB (112 instances)
L3 cache:                             600 MiB (2 instances)
NUMA node(s):                         2
NUMA node0 CPU(s):                    0-55,112-167
NUMA node1 CPU(s):                    56-111,168-223
Vulnerability Gather data sampling:   Not affected
Vulnerability Itlb multihit:          Not affected
Vulnerability L1tf:                   Not affected
Vulnerability Mds:                    Not affected
Vulnerability Meltdown:               Not affected
Vulnerability Mmio stale data:        Not affected
Vulnerability Reg file data sampling: Not affected
Vulnerability Retbleed:               Not affected
Vulnerability Spec rstack overflow:   Not affected
Vulnerability Spec store bypass:      Mitigation; Speculative Store Bypass disabled via prctl
Vulnerability Spectre v1:             Mitigation; usercopy/swapgs barriers and __user pointer sanitization
Vulnerability Spectre v2:             Mitigation; Enhanced / Automatic IBRS; IBPB conditional; RSB filling; PBRSB-eIBRS SW sequence; BHI BHI_DIS_S
Vulnerability Srbds:                  Not affected
Vulnerability Tsx async abort:        Not affected
Vulnerability Vmscape:                Mitigation; IBPB before exit to userspace

==============================
Versions of relevant libraries
==============================
[pip3] flashinfer-python==0.6.8.post1
[pip3] numpy==2.2.6
[pip3] nvidia-cublas==13.1.0.3
[pip3] nvidia-cublas-cu12==12.9.1.4
[pip3] nvidia-cuda-cupti==13.0.85
[pip3] nvidia-cuda-cupti-cu12==12.9.79
[pip3] nvidia-cuda-nvrtc==13.0.88
[pip3] nvidia-cuda-nvrtc-cu12==12.9.86
[pip3] nvidia-cuda-runtime==13.0.96
[pip3] nvidia-cuda-runtime-cu12==12.9.79
[pip3] nvidia-cudnn-cu12==9.10.2.21
[pip3] nvidia-cudnn-cu13==9.19.0.56
[pip3] nvidia-cudnn-frontend==1.18.0
[pip3] nvidia-cufft==12.0.0.61
[pip3] nvidia-cufft-cu12==11.4.1.4
[pip3] nvidia-cufile==1.15.1.6
[pip3] nvidia-cufile-cu12==1.14.1.1
[pip3] nvidia-curand==10.4.0.35
[pip3] nvidia-curand-cu12==10.3.10.19
[pip3] nvidia-cusolver==12.0.4.66
[pip3] nvidia-cusolver-cu12==11.7.5.82
[pip3] nvidia-cusparse==12.6.3.3
[pip3] nvidia-cusparse-cu12==12.5.10.65
[pip3] nvidia-cusparselt-cu12==0.7.1
[pip3] nvidia-cusparselt-cu13==0.8.0
[pip3] nvidia-cutlass-dsl==4.4.2
[pip3] nvidia-cutlass-dsl-libs-base==4.4.2
[pip3] nvidia-ml-py==13.590.48
[pip3] nvidia-nccl-cu12==2.27.5
[pip3] nvidia-nccl-cu13==2.28.9
[pip3] nvidia-nvjitlink==13.0.88
[pip3] nvidia-nvjitlink-cu12==12.9.86
[pip3] nvidia-nvshmem-cu12==3.4.5
[pip3] nvidia-nvshmem-cu13==3.4.5
[pip3] nvidia-nvtx==13.0.85
[pip3] nvidia-nvtx-cu12==12.9.79
[pip3] pyzmq==27.1.0
[pip3] torch==2.11.0+cu130
[pip3] torch-c-dlpack-ext==0.1.5
[pip3] torchaudio==2.11.0+cu130
[pip3] torchvision==0.26.0+cu130
[pip3] transformers==4.57.6
[pip3] triton==3.6.0
[conda] Could not collect

==============================
         vLLM Info
==============================
ROCM Version                 : Could not collect
vLLM Version                 : 0.19.2rc1.dev47+g191e3fdaa (git sha: 191e3fdaa)
vLLM Build Flags:
  CUDA Archs: Not Set; ROCm: Disabled; XPU: Disabled
GPU Topology:
  	GPU0	GPU1	GPU2	GPU3	GPU4	GPU5	GPU6	GPU7	NIC0	NIC1	NIC2	NIC3	NIC4	NIC5	NIC6	NIC7	NIC8	NIC9	NIC10	NIC11	NIC12	NIC13	NIC14	NIC15	CPU Affinity	NUMA Affinity	GPU NUMA ID
GPU0	 X 	NV18	NV18	NV18	NV18	NV18	NV18	NV18	NODE	NODE	NODE	NODE	PXB	NODE	NODE	NODE	NODE	NODE	SYS	SYS	SYS	SYS	SYS	SYS	0-55,112-167	0		N/A
GPU1	NV18	 X 	NV18	NV18	NV18	NV18	NV18	NV18	NODE	NODE	NODE	NODE	NODE	NODE	NODE	PXB	NODE	NODE	SYS	SYS	SYS	SYS	SYS	SYS	0-55,112-167	0		N/A
GPU2	NV18	NV18	 X 	NV18	NV18	NV18	NV18	NV18	NODE	NODE	NODE	NODE	NODE	NODE	NODE	NODE	PXB	NODE	SYS	SYS	SYS	SYS	SYS	SYS	0-55,112-167	0		N/A
GPU3	NV18	NV18	NV18	 X 	NV18	NV18	NV18	NV18	NODE	NODE	NODE	NODE	NODE	NODE	NODE	NODE	NODE	PXB	SYS	SYS	SYS	SYS	SYS	SYS	0-55,112-167	0		N/A
GPU4	NV18	NV18	NV18	NV18	 X 	NV18	NV18	NV18	SYS	SYS	SYS	SYS	SYS	SYS	SYS	SYS	SYS	SYS	PXB	NODE	NODE	NODE	NODE	NODE	56-111,168-223	1		N/A
GPU5	NV18	NV18	NV18	NV18	NV18	 X 	NV18	NV18	SYS	SYS	SYS	SYS	SYS	SYS	SYS	SYS	SYS	SYS	NODE	NODE	NODE	PXB	NODE	NODE	56-111,168-223	1		N/A
GPU6	NV18	NV18	NV18	NV18	NV18	NV18	 X 	NV18	SYS	SYS	SYS	SYS	SYS	SYS	SYS	SYS	SYS	SYS	NODE	NODE	NODE	NODE	PXB	NODE	56-111,168-223	1		N/A
GPU7	NV18	NV18	NV18	NV18	NV18	NV18	NV18	 X 	SYS	SYS	SYS	SYS	SYS	SYS	SYS	SYS	SYS	SYS	NODE	NODE	NODE	NODE	NODE	PXB	56-111,168-223	1		N/A
NIC0	NODE	NODE	NODE	NODE	SYS	SYS	SYS	SYS	 X 	PIX	PIX	PIX	NODE	NODE	NODE	NODE	NODE	NODE	SYS	SYS	SYS	SYS	SYS	SYS				
NIC1	NODE	NODE	NODE	NODE	SYS	SYS	SYS	SYS	PIX	 X 	PIX	PIX	NODE	NODE	NODE	NODE	NODE	NODE	SYS	SYS	SYS	SYS	SYS	SYS				
NIC2	NODE	NODE	NODE	NODE	SYS	SYS	SYS	SYS	PIX	PIX	 X 	PIX	NODE	NODE	NODE	NODE	NODE	NODE	SYS	SYS	SYS	SYS	SYS	SYS				
NIC3	NODE	NODE	NODE	NODE	SYS	SYS	SYS	SYS	PIX	PIX	PIX	 X 	NODE	NODE	NODE	NODE	NODE	NODE	SYS	SYS	SYS	SYS	SYS	SYS				
NIC4	PXB	NODE	NODE	NODE	SYS	SYS	SYS	SYS	NODE	NODE	NODE	NODE	 X 	NODE	NODE	NODE	NODE	NODE	SYS	SYS	SYS	SYS	SYS	SYS				
NIC5	NODE	NODE	NODE	NODE	SYS	SYS	SYS	SYS	NODE	NODE	NODE	NODE	NODE	 X 	PIX	NODE	NODE	NODE	SYS	SYS	SYS	SYS	SYS	SYS				
NIC6	NODE	NODE	NODE	NODE	SYS	SYS	SYS	SYS	NODE	NODE	NODE	NODE	NODE	PIX	 X 	NODE	NODE	NODE	SYS	SYS	SYS	SYS	SYS	SYS				
NIC7	NODE	PXB	NODE	NODE	SYS	SYS	SYS	SYS	NODE	NODE	NODE	NODE	NODE	NODE	NODE	 X 	NODE	NODE	SYS	SYS	SYS	SYS	SYS	SYS				
NIC8	NODE	NODE	PXB	NODE	SYS	SYS	SYS	SYS	NODE	NODE	NODE	NODE	NODE	NODE	NODE	NODE	 X 	NODE	SYS	SYS	SYS	SYS	SYS	SYS				
NIC9	NODE	NODE	NODE	PXB	SYS	SYS	SYS	SYS	NODE	NODE	NODE	NODE	NODE	NODE	NODE	NODE	NODE	 X 	SYS	SYS	SYS	SYS	SYS	SYS				
NIC10	SYS	SYS	SYS	SYS	PXB	NODE	NODE	NODE	SYS	SYS	SYS	SYS	SYS	SYS	SYS	SYS	SYS	SYS	 X 	NODE	NODE	NODE	NODE	NODE				
NIC11	SYS	SYS	SYS	SYS	NODE	NODE	NODE	NODE	SYS	SYS	SYS	SYS	SYS	SYS	SYS	SYS	SYS	SYS	NODE	 X 	PIX	NODE	NODE	NODE				
NIC12	SYS	SYS	SYS	SYS	NODE	NODE	NODE	NODE	SYS	SYS	SYS	SYS	SYS	SYS	SYS	SYS	SYS	SYS	NODE	PIX	 X 	NODE	NODE	NODE				
NIC13	SYS	SYS	SYS	SYS	NODE	PXB	NODE	NODE	SYS	SYS	SYS	SYS	SYS	SYS	SYS	SYS	SYS	SYS	NODE	NODE	NODE	 X 	NODE	NODE				
NIC14	SYS	SYS	SYS	SYS	NODE	NODE	PXB	NODE	SYS	SYS	SYS	SYS	SYS	SYS	SYS	SYS	SYS	SYS	NODE	NODE	NODE	NODE	 X 	NODE				
NIC15	SYS	SYS	SYS	SYS	NODE	NODE	NODE	PXB	SYS	SYS	SYS	SYS	SYS	SYS	SYS	SYS	SYS	SYS	NODE	NODE	NODE	NODE	NODE	 X 				

Legend:

  X    = Self
  SYS  = Connection traversing PCIe as well as the SMP interconnect between NUMA nodes (e.g., QPI/UPI)
  NODE = Connection traversing PCIe as well as the interconnect between PCIe Host Bridges within a NUMA node
  PHB  = Connection traversing PCIe as well as a PCIe Host Bridge (typically the CPU)
  PXB  = Connection traversing multiple PCIe bridges (without traversing the PCIe Host Bridge)
  PIX  = Connection traversing at most a single PCIe bridge
  NV#  = Connection traversing a bonded set of # NVLinks

NIC Legend:

  NIC0: mlx5_0
  NIC1: mlx5_1
  NIC2: mlx5_2
  NIC3: mlx5_3
  NIC4: mlx5_4
  NIC5: mlx5_5
  NIC6: mlx5_6
  NIC7: mlx5_7
  NIC8: mlx5_8
  NIC9: mlx5_9
  NIC10: mlx5_10
  NIC11: mlx5_11
  NIC12: mlx5_12
  NIC13: mlx5_13
  NIC14: mlx5_14
  NIC15: mlx5_15

==============================
     Environment Variables
==============================
NVIDIA_VISIBLE_DEVICES=GPU-8317f78c-f99d-83bd-c482-32dac10ef30c,GPU-8fc7a7b6-bcef-c33d-4892-d0fede2d5f0f,GPU-b37834f6-e251-1183-1917-a2e8b43b9fc4,GPU-13fa1039-be1e-010e-413e-36eec85e98f8,GPU-d878248b-2c48-d6bc-373f-f4fa503999bf,GPU-73ea9b4f-1089-1e83-fbe5-1e20e9021147,GPU-12f455bd-4fb9-9ac5-d065-962815ef9675,GPU-d34404df-593a-d600-db7e-7b4b3bbeec38
CUDA_MPS_PIPE_DIRECTORY=/tmp/nvidia-mps/job-2100478
CUDA_VISIBLE_DEVICES=0,1,2,3,4,5,6,7
CUDA_VISIBLE_DEVICES=0,1,2,3,4,5,6,7
CUDA_MPS_LOG_DIRECTORY=/tmp/nvidia-mps/job-2100478/logs
LD_LIBRARY_PATH=/home/scratch.vgimpelson_ent/cuda/cuda130/lib64:
CUDA_HOME=/home/scratch.vgimpelson_ent/cuda/cuda130
CUDA_HOME=/home/scratch.vgimpelson_ent/cuda/cuda130
PYTORCH_NVML_BASED_CUDA_CHECK=1
TORCHINDUCTOR_COMPILE_THREADS=1
TORCHINDUCTOR_CACHE_DIR=/tmp/vgimpelson/torchinductor_vgimpelson
</details>

🐛 Describe the bug

Summary

Running the standard vllm bench serve against the vllm serve of Qwen3.5-397B-A17B-NVFP4 with data parallelism + expert parallelism on 8× B200 hangs the workers a few hundred requests into the bench. The engine eventually times out on its IPC dequeue and turns into a EngineDeadError.

Bisect (vLLM-side, between adjacent first-parent commits) isolates the regression to PR vllm-project/vllm#39959 "Update flashinfer to 0.6.8", and within that PR to the flashinfer-python 0.6.7 → 0.6.8.post1 version pin in requirements/cuda.txt. Pinning flashinfer back to 0.6.7 on the first-bad vLLM commit restores 1024/1024 PASS.

Update. flashinfer v0.6.11 doesn't fix the bug.

Environment

  • vLLM (affected): every commit at or after 191e3fdaa1fd3dd09441e7b22d4f2ddef51c012c (2026-04-20 17:37 UTC, PR vllm-project/vllm#39959). This includes the v0.19.1, v0.20.0, and v0.20.1 releases and current main.
  • vLLM (last known good): b9cf629bd0e924c69f3d8bfefbfdb77df5ffc7be (2026-04-20 17:31 UTC) — the immediate predecessor on first-parent.
  • flashinfer-python==0.6.8.post1, flashinfer-cubin==0.6.8.post1 (the version pin introduced by #39959; 0.6.7 of both packages is what worked).
  • 8× NVIDIA B200 (SM100), CUDA 12.8 host driver
  • Model: nvidia/Qwen3.5-397B-A17B-NVFP4. Selects [Using 'FLASHINFER_TRTLLM' NvFp4 MoE backend].

IMPORTANT

On another server in another cluster but exactly the same 8*B200, there is no hang.

<details> <summary>The output of <code>python collect_env.py</code> from the second server</summary>
==============================
        System Info
==============================
OS                           : Ubuntu 24.04.4 LTS (x86_64)
GCC version                  : (Ubuntu 13.3.0-6ubuntu2~24.04.1) 13.3.0
Clang version                : Could not collect
CMake version                : Could not collect
Libc version                 : glibc-2.39

==============================
       PyTorch Info
==============================
PyTorch version              : 2.11.0+cu130
Is debug build               : False
CUDA used to build PyTorch   : 13.0
ROCM used to build PyTorch   : N/A
XPU used to build PyTorch    : N/A

==============================
      Python Environment
==============================
Python version               : 3.12.3 (main, Jan 22 2026, 20:57:42) [GCC 13.3.0] (64-bit runtime)
Python platform              : Linux-6.14.0-37-generic-x86_64-with-glibc2.39

==============================
       CUDA / GPU Info
==============================
Is CUDA available            : True
CUDA runtime version         : 12.8.61
CUDA_MODULE_LOADING set to   :
GPU models and configuration :
GPU 0: NVIDIA B200
GPU 1: NVIDIA B200
GPU 2: NVIDIA B200
GPU 3: NVIDIA B200
GPU 4: NVIDIA B200
GPU 5: NVIDIA B200
GPU 6: NVIDIA B200
GPU 7: NVIDIA B200

Nvidia driver version        : 580.126.09
cuDNN version                : Could not collect
HIP runtime version          : N/A
MIOpen runtime version       : N/A
Is XNNPACK available         : True

==============================
          CPU Info
==============================
Architecture:                            x86_64
CPU op-mode(s):                          32-bit, 64-bit
Address sizes:                           52 bits physical, 57 bits virtual
Byte Order:                              Little Endian
CPU(s):                                  224
On-line CPU(s) list:                     0-223
Vendor ID:                               GenuineIntel
Model name:                              INTEL(R) XEON(R) PLATINUM 8570
CPU family:                              6
Model:                                   207
Thread(s) per core:                      2
Core(s) per socket:                      56
Socket(s):                               2
Stepping:                                2
CPU(s) scaling MHz:                      49%
CPU max MHz:                             4000.0000
CPU min MHz:                             800.0000
BogoMIPS:                                4200.00
Flags:                                   fpu vme de pse tsc msr pae mce cx8 apic sep mtrr pge mca cmov pat pse36 clflush dts acpi mmx fxsr sse sse2 ss ht tm pbe syscall nx pdpe1gb rdtscp lm constant_tsc art arch_perfmon pebs bts rep_good nopl xtopology nonstop_tsc cpuid aperfmperf tsc_known_freq pni pclmulqdq dtes64 monitor ds_cpl vmx smx est tm2 ssse3 sdbg fma cx16 xtpr pdcm pcid dca sse4_1 sse4_2 x2apic movbe popcnt tsc_deadline_timer aes xsave avx f16c rdrand lahf_lm abm 3dnowprefetch cpuid_fault epb cat_l3 cat_l2 cdp_l3 intel_ppin cdp_l2 ssbd mba ibrs ibpb stibp ibrs_enhanced tpr_shadow flexpriority ept vpid ept_ad fsgsbase tsc_adjust bmi1 avx2 smep bmi2 erms invpcid cqm rdt_a avx512f avx512dq rdseed adx smap avx512ifma clflushopt clwb intel_pt avx512cd sha_ni avx512bw avx512vl xsaveopt xsavec xgetbv1 xsaves cqm_llc cqm_occup_llc cqm_mbm_total cqm_mbm_local split_lock_detect user_shstk avx_vnni avx512_bf16 wbnoinvd dtherm ida arat pln pts hwp hwp_act_window hwp_epp hwp_pkg_req vnmi avx512vbmi umip pku ospke waitpkg avx512_vbmi2 gfni vaes vpclmulqdq avx512_vnni avx512_bitalg avx512_vpopcntdq la57 rdpid bus_lock_detect cldemote movdiri movdir64b enqcmd fsrm md_clear serialize tsxldtrk pconfig arch_lbr ibt amx_bf16 avx512_fp16 amx_tile amx_int8 flush_l1d arch_capabilities
Virtualization:                          VT-x
L1d cache:                               5.3 MiB (112 instances)
L1i cache:                               3.5 MiB (112 instances)
L2 cache:                                224 MiB (112 instances)
L3 cache:                                600 MiB (2 instances)
NUMA node(s):                            2
NUMA node0 CPU(s):                       0-55,112-167
NUMA node1 CPU(s):                       56-111,168-223
Vulnerability Gather data sampling:      Not affected
Vulnerability Ghostwrite:                Not affected
Vulnerability Indirect target selection: Not affected
Vulnerability Itlb multihit:             Not affected
Vulnerability L1tf:                      Not affected
Vulnerability Mds:                       Not affected
Vulnerability Meltdown:                  Not affected
Vulnerability Mmio stale data:           Not affected
Vulnerability Reg file data sampling:    Not affected
Vulnerability Retbleed:                  Not affected
Vulnerability Spec rstack overflow:      Not affected
Vulnerability Spec store bypass:         Vulnerable
Vulnerability Spectre v1:                Vulnerable: __user pointer sanitization and usercopy barriers only; no swapgs barriers
Vulnerability Spectre v2:                Vulnerable; IBPB: disabled; STIBP: disabled; PBRSB-eIBRS: Vulnerable; BHI: Vulnerable
Vulnerability Srbds:                     Not affected
Vulnerability Tsa:                       Not affected
Vulnerability Tsx async abort:           Not affected
Vulnerability Vmscape:                   Vulnerable

==============================
Versions of relevant libraries
==============================
[pip3] flashinfer-python==0.6.8.post1
[pip3] numpy==2.2.6
[pip3] nvidia-cublas==13.1.0.3
[pip3] nvidia-cuda-cupti==13.0.85
[pip3] nvidia-cuda-nvrtc==13.0.88
[pip3] nvidia-cuda-runtime==13.0.96
[pip3] nvidia-cudnn-cu13==9.19.0.56
[pip3] nvidia-cudnn-frontend==1.18.0
[pip3] nvidia-cufft==12.0.0.61
[pip3] nvidia-cufile==1.15.1.6
[pip3] nvidia-curand==10.4.0.35
[pip3] nvidia-cusolver==12.0.4.66
[pip3] nvidia-cusparse==12.6.3.3
[pip3] nvidia-cusparselt-cu13==0.8.0
[pip3] nvidia-cutlass-dsl==4.5.0
[pip3] nvidia-cutlass-dsl-libs-base==4.5.0
[pip3] nvidia-ml-py==13.595.45
[pip3] nvidia-nccl-cu13==2.28.9
[pip3] nvidia-nvjitlink==13.0.88
[pip3] nvidia-nvshmem-cu13==3.4.5
[pip3] nvidia-nvtx==13.0.85
[pip3] pyzmq==27.1.0
[pip3] torch==2.11.0+cu130
[pip3] torch_c_dlpack_ext==0.1.5
[pip3] torchaudio==2.11.0+cu130
[pip3] torchvision==0.26.0+cu130
[pip3] transformers==5.8.0
[pip3] triton==3.6.0
[conda] Could not collect

==============================
         vLLM Info
==============================
ROCM Version                 : Could not collect
vLLM Version                 : 0.19.2rc1.dev47+g191e3fdaa (git sha: 191e3fdaa)
vLLM Build Flags:
  CUDA Archs: Not Set; ROCm: Disabled; XPU: Disabled
GPU Topology:
        GPU0    GPU1    GPU2    GPU3    GPU4    GPU5    GPU6    GPU7    NIC0    NIC1    NIC2    NIC3    NIC4    NIC5    NIC6   NIC7     NIC8    NIC9    NIC10   NIC11   NIC12   NIC13   NIC14   NIC15   CPU Affinity    NUMA Affinity   GPU NUMA ID
GPU0     X      NV18    NV18    NV18    NV18    NV18    NV18    NV18    NODE    NODE    NODE    NODE    PXB     NODE    NODE   NODE     NODE    NODE    SYS     SYS     SYS     SYS     SYS     SYS     0-55,112-167    0               N/A
GPU1    NV18     X      NV18    NV18    NV18    NV18    NV18    NV18    NODE    NODE    NODE    NODE    NODE    NODE    NODE   PXB      NODE    NODE    SYS     SYS     SYS     SYS     SYS     SYS     0-55,112-167    0               N/A
GPU2    NV18    NV18     X      NV18    NV18    NV18    NV18    NV18    NODE    NODE    NODE    NODE    NODE    NODE    NODE   NODE     PXB     NODE    SYS     SYS     SYS     SYS     SYS     SYS     0-55,112-167    0               N/A
GPU3    NV18    NV18    NV18     X      NV18    NV18    NV18    NV18    NODE    NODE    NODE    NODE    NODE    NODE    NODE   NODE     NODE    PXB     SYS     SYS     SYS     SYS     SYS     SYS     0-55,112-167    0               N/A
GPU4    NV18    NV18    NV18    NV18     X      NV18    NV18    NV18    SYS     SYS     SYS     SYS     SYS     SYS     SYS    SYS      SYS     SYS     PXB     NODE    NODE    NODE    NODE    NODE    56-111,168-223  1               N/A
GPU5    NV18    NV18    NV18    NV18    NV18     X      NV18    NV18    SYS     SYS     SYS     SYS     SYS     SYS     SYS    SYS      SYS     SYS     NODE    NODE    NODE    PXB     NODE    NODE    56-111,168-223  1               N/A
GPU6    NV18    NV18    NV18    NV18    NV18    NV18     X      NV18    SYS     SYS     SYS     SYS     SYS     SYS     SYS    SYS      SYS     SYS     NODE    NODE    NODE    NODE    PXB     NODE    56-111,168-223  1               N/A
GPU7    NV18    NV18    NV18    NV18    NV18    NV18    NV18     X      SYS     SYS     SYS     SYS     SYS     SYS     SYS    SYS      SYS     SYS     NODE    NODE    NODE    NODE    NODE    PXB     56-111,168-223  1               N/A
NIC0    NODE    NODE    NODE    NODE    SYS     SYS     SYS     SYS      X      PIX     PIX     PIX     NODE    NODE    NODE   NODE     NODE    NODE    SYS     SYS     SYS     SYS     SYS     SYS
NIC1    NODE    NODE    NODE    NODE    SYS     SYS     SYS     SYS     PIX      X      PIX     PIX     NODE    NODE    NODE   NODE     NODE    NODE    SYS     SYS     SYS     SYS     SYS     SYS
NIC2    NODE    NODE    NODE    NODE    SYS     SYS     SYS     SYS     PIX     PIX      X      PIX     NODE    NODE    NODE   NODE     NODE    NODE    SYS     SYS     SYS     SYS     SYS     SYS
NIC3    NODE    NODE    NODE    NODE    SYS     SYS     SYS     SYS     PIX     PIX     PIX      X      NODE    NODE    NODE   NODE     NODE    NODE    SYS     SYS     SYS     SYS     SYS     SYS
NIC4    PXB     NODE    NODE    NODE    SYS     SYS     SYS     SYS     NODE    NODE    NODE    NODE     X      NODE    NODE   NODE     NODE    NODE    SYS     SYS     SYS     SYS     SYS     SYS
NIC5    NODE    NODE    NODE    NODE    SYS     SYS     SYS     SYS     NODE    NODE    NODE    NODE    NODE     X      PIX    NODE     NODE    NODE    SYS     SYS     SYS     SYS     SYS     SYS
NIC6    NODE    NODE    NODE    NODE    SYS     SYS     SYS     SYS     NODE    NODE    NODE    NODE    NODE    PIX      X     NODE     NODE    NODE    SYS     SYS     SYS     SYS     SYS     SYS
NIC7    NODE    PXB     NODE    NODE    SYS     SYS     SYS     SYS     NODE    NODE    NODE    NODE    NODE    NODE    NODE    X       NODE    NODE    SYS     SYS     SYS     SYS     SYS     SYS
NIC8    NODE    NODE    PXB     NODE    SYS     SYS     SYS     SYS     NODE    NODE    NODE    NODE    NODE    NODE    NODE   NODE      X      NODE    SYS     SYS     SYS     SYS     SYS     SYS
NIC9    NODE    NODE    NODE    PXB     SYS     SYS     SYS     SYS     NODE    NODE    NODE    NODE    NODE    NODE    NODE   NODE     NODE     X      SYS     SYS     SYS     SYS     SYS     SYS
NIC10   SYS     SYS     SYS     SYS     PXB     NODE    NODE    NODE    SYS     SYS     SYS     SYS     SYS     SYS     SYS    SYS      SYS     SYS      X      NODE    NODE    NODE    NODE    NODE
NIC11   SYS     SYS     SYS     SYS     NODE    NODE    NODE    NODE    SYS     SYS     SYS     SYS     SYS     SYS     SYS    SYS      SYS     SYS     NODE     X      PIX     NODE    NODE    NODE
NIC12   SYS     SYS     SYS     SYS     NODE    NODE    NODE    NODE    SYS     SYS     SYS     SYS     SYS     SYS     SYS    SYS      SYS     SYS     NODE    PIX      X      NODE    NODE    NODE
NIC13   SYS     SYS     SYS     SYS     NODE    PXB     NODE    NODE    SYS     SYS     SYS     SYS     SYS     SYS     SYS    SYS      SYS     SYS     NODE    NODE    NODE     X      NODE    NODE
NIC14   SYS     SYS     SYS     SYS     NODE    NODE    PXB     NODE    SYS     SYS     SYS     SYS     SYS     SYS     SYS    SYS      SYS     SYS     NODE    NODE    NODE    NODE     X      NODE
NIC15   SYS     SYS     SYS     SYS     NODE    NODE    NODE    PXB     SYS     SYS     SYS     SYS     SYS     SYS     SYS    SYS      SYS     SYS     NODE    NODE    NODE    NODE    NODE     X

Legend:

  X    = Self
  SYS  = Connection traversing PCIe as well as the SMP interconnect between NUMA nodes (e.g., QPI/UPI)
  NODE = Connection traversing PCIe as well as the interconnect between PCIe Host Bridges within a NUMA node
  PHB  = Connection traversing PCIe as well as a PCIe Host Bridge (typically the CPU)
  PXB  = Connection traversing multiple PCIe bridges (without traversing the PCIe Host Bridge)
  PIX  = Connection traversing at most a single PCIe bridge
  NV#  = Connection traversing a bonded set of # NVLinks

NIC Legend:

  NIC0: mlx5_0
  NIC1: mlx5_1
  NIC2: mlx5_2
  NIC3: mlx5_3
  NIC4: mlx5_4
  NIC5: mlx5_5
  NIC6: mlx5_6
  NIC7: mlx5_7
  NIC8: mlx5_8
  NIC9: mlx5_9
  NIC10: mlx5_10
  NIC11: mlx5_11
  NIC12: mlx5_12
  NIC13: mlx5_13
  NIC14: mlx5_14
  NIC15: mlx5_15

==============================
     Environment Variables
==============================
LD_LIBRARY_PATH=/home/aperevedents/storage/cuda/cuda128/lib64:
CUDA_HOME=/home/aperevedents/storage/cuda/cuda128
CUDA_HOME=/home/aperevedents/storage/cuda/cuda128
PYTORCH_NVML_BASED_CUDA_CHECK=1
TORCHINDUCTOR_COMPILE_THREADS=1
TORCHINDUCTOR_CACHE_DIR=/tmp/torchinductor_aperevedents
</details> I don't see any important difference except driver version.

Reproducer

Server (one shell, all 8 B200s):

vllm serve nvidia/Qwen3.5-397B-A17B-NVFP4 \
    --port 8000 \
    -tp 1 -pp 1 -dp 8 \
    --enable-expert-parallel \
    --language-model-only \
    --reasoning-parser qwen3 \
    --stream-interval 100

Client (after Application startup complete):

vllm bench serve --backend vllm \
    --model nvidia/Qwen3.5-397B-A17B-NVFP4 \
    --port 8000 \
    --endpoint /v1/completions \
    --ignore-eos --temperature 0.0 \
    --dataset-name random --random-input 8192 --random-output 1 \
    --num-prompt 1024 --max-concurrency 128

Failure

The server takes traffic for N requests (observed N: 72…632 across runs — the hang is non-deterministic but triggers reliably within one 1024-prompt bench). Then all 8 engine cores log:

shm_broadcast.py:681 ... No available shared memory broadcast block found in 60 seconds.
This typically happens when some processes are hanging or doing some time-consuming
work (e.g. compilation, weight/kv cache quantization).

repeating every 60 s for ~5 minutes. Then the executor's mq.dequeue times out and the engine raises:

File "vllm/v1/executor/multiproc_executor.py", line 386, in get_response
    status, result = mq.dequeue(timeout=dequeue_timeout)
File "vllm/distributed/device_communicators/shm_broadcast.py", line 631, in timeout_ms
    raise TimeoutError
TimeoutError

The above exception was the direct cause of the following exception:

(EngineCore_DPx) ERROR ... [core.py:1138] EngineCore encountered a fatal error.
vllm.v1.engine.exceptions.EngineDeadError: EngineCore encountered an issue.

Subsequent requests then return HTTP 500 until the server is killed.

The signal is consistent with the worker process's CUDA queue stalling inside the MoE forward (workers stop responding to the executor's IPC requests), not a Python-level deadlock.

Bisect

BoundSHAflashinferVerdict
last goodb9cf629bd0e924c69f3d8bfefbfdb77df5ffc7be0.6.7PASS (1024/1024)
first bad191e3fdaa1fd3dd09441e7b22d4f2ddef51c012c (PR #39959)0.6.8.post1FAIL (≤300/1024 + 500s + EngineDeadError)

These two commits are adjacent on origin/main's first-parent line — the regression is uniquely #39959.

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vllm - 💡(How to fix) Fix [Bug][flashinfer 0.6.8]: worker hang on Qwen3.5-397B-A17B-NVFP4 EP=8 (B200 SM100) - bisected to flashinfer-python 0.6.7 → 0.6.8.post1