TRUTH SOCIAL: NVLink multicast is not supported on Blackwell "Confidential Computing" leading to 61% performance regress…

SemiAnalysis Twitter · SemiAnalysis (@SemiAnalysis_) · 2026-05-30

NVIDIA's Blackwell GPUs in "Confidential Computing" mode lack NVLink multicast support, causing a 61% inference performance regression on SGLang Qwen3.5 397B workloads, according to a Verdacloud GitHub report.

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NVIDIA GPU Ecosystem Performance Gaps: JAX Dropout, Blackwell Regression, and Kernel Utilization

Extraction

Topics: nvidia-blackwellconfidential-computingnvlinkinference-performancegpu-hardware

Claims

NVLink multicast is unsupported in NVIDIA Blackwell's Confidential Computing mode.
This limitation causes a 61% performance regression on SGLang Qwen3.5 397B inference workloads.
NVIDIA's Confidential Computing feature has significant performance and functionality gaps across both Hopper and Blackwell architectures.

Key quotes

NVLink multicast is not supported on Blackwell 'Confidential Computing' leading to 61% performance regression on SGLang Qwen3.5 397B.

NVIDIA's 'Confidential Computing' is complete slop.