NVLink Error
NVLink errors cause intra-node GPU communication failures and degraded multi-GPU performance.
NVLink errors cause intra-node GPU communication failures and degraded multi-GPU performance.
What this failure is
NVLink Error is a Hardware failure seen during ML training runs. NVLink errors cause intra-node GPU communication failures and degraded multi-GPU performance. Common tags: Nvlink, Gpu, Hardware, P2p.
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Why it happens (the mechanism)
NVLink hardware fault. Loose NVLink connector. NVLink firmware mismatch. GPU seating issue. Taken together, these mechanisms explain why the failure is reproducible, why it tends to surface on specific workloads or scales, and why generic mitigation attempts often fall short without addressing the underlying cause.
What you'll observe
- P2P communication between GPUs on same node fails
- NCCL performance is poor on multi-GPU nodes
- NVLink link is down for some GPU pairs
Common symptoms and what they mean
| Symptom | Why it happens |
|---|---|
| dmesg: nvlink: link X is down | NVLink hardware fault |
| nvidia-smi nvlink --link shows link down | Loose NVLink connector |
| NCCL warnings about P2P link issues | NVLink firmware mismatch |
| NCCL falls back to slower PCIe for intra-node communication | GPU seating issue |
Which systems are affected
- Multi-GPU nodes (8 GPUs per node)
- DGX systems with NVLink
- Nodes with GPUs across multiple NVLink islands
How to confirm this is the problem
Use this checklist to test the hypothesis against a small reproduction. No single line proves the root cause, so preserve the preceding events and compare one variable at a time.
- ✓Reproduce the failure from a clean checkpoint/seed: the symptom must appear without warm-up state from a previous run.
- ✓Verified signal present: dmesg: nvlink: link X is down
- ✓Verified signal present: nvidia-smi nvlink --link shows link down
- ✓Verified signal present: NCCL warnings about P2P link issues
- ✓Verified signal present: NCCL falls back to slower PCIe for intra-node communication
- ✓A targeted fix from the "How to fix it" section eliminates or substantially reduces the symptom within one validation pass.
The fix and the prevention pattern
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Root cause
- NVLink hardware fault
- Loose NVLink connector
- NVLink firmware mismatch
- GPU seating issue
The fix and how to prevent it
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