DCGM_FI_DEV_NVLINK_CRC_FLIT_ERROR counter incremented link degraded

DCGM observed an increase in NVLink CRC flit errors and marked the link degraded. A rising counter indicates signal or link integrity trouble, not a collective software timeout. This entry explains how to confirm the cause, apply the fix, and separate it from adjacent nvlink failures.

Symptom

DCGM_FI_DEV_NVLINK_CRC_FLIT_ERROR counter incremented link degraded

Root cause

DCGM observed an increase in NVLink CRC flit errors and marked the link degraded. A rising counter indicates signal or link integrity trouble, not a collective software timeout. The decisive evidence is the first log line that precedes "DCGM_FI_DEV_NVLINK_CRC_FLIT_ERROR counter incremented link degraded" and differs from a healthy run.

Recommended fix

identify the GPU and link ID, stop placing new multi-GPU work across that path, and record the counter before any reset.

How Denpex helps

Denpex investigates DCGM_FI_DEV_NVLINK_CRC_FLIT_ERROR counter incremented link degraded using the evidence you provide or your connected workload collects. Earlier rank, host or application evidence is needed to distinguish an initiating failure from a downstream report.

The literal signature is "DCGM_FI_DEV_NVLINK_CRC_FLIT_ERROR counter incremented link degraded". It is a hardware failure associated with NVLink, NVSwitch, DGX, and HGX systems. The line identifies the failing operation or subsystem, while the surrounding evidence decides whether it is the initiating fault or a downstream symptom.

DCGM observed an increase in NVLink CRC flit errors and marked the link degraded. A rising counter indicates signal or link integrity trouble, not a collective software timeout. The failure becomes visible at this call site because the operation first requires the missing resource, valid state, healthy peer, or correct result. Earlier log lines and a known-good control carry more causal value than the final wrapper exception.

• The workload stops or loses forward progress after emitting "DCGM_FI_DEV_NVLINK_CRC_FLIT_ERROR counter incremented link degraded".
• A retry on the same configuration reproduces the failure because the causal state has not changed.
• The outer framework exception can hide the rank, node, allocation, or dependency that failed first.
• Increasing timeouts or reducing workload size can suppress the symptom without correcting the cause.

• NVLink, NVSwitch, DGX, and HGX systems
• production-shaped multi-accelerator workloads
• containerized and bare-metal deployments of the same stack

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.

• ✓Find the first occurrence of "DCGM_FI_DEV_NVLINK_CRC_FLIT_ERROR counter incremented link degraded" and preserve at least 100 lines before it.
• ✓Identify which rank, node, device, or process emitted the first related warning.
• ✓compare counters on both endpoints, inspect link state and recovery events, and run a topology-aware DCGM or NVLink bandwidth control.
• ✓Repeat the same input after the targeted change and require the signature to disappear.
• ✓Resume from latest checkpoint on a topology that excludes the degraded link only after the control passes.

• DCGM observed an increase in NVLink CRC flit errors and marked the link degraded. A rising counter indicates signal or link integrity trouble, not a collective software timeout.
• The decisive evidence is the first log line that precedes "DCGM_FI_DEV_NVLINK_CRC_FLIT_ERROR counter incremented link degraded" and differs from a healthy run.
• A nearby failure remains a competing hypothesis until a control separates configuration, capacity, transport, and hardware causes.

DCGM_FI_DEV_NVLINK_CRC_FLIT_ERROR counter incremented link degraded

Use this text as a lookup key in logs and upstream issue trackers. It is not presented as a captured customer log. Confirm the cause from your own preceding events, versions, configuration and the cited references.

identify the GPU and link ID, stop placing new multi-GPU work across that path, and record the counter before any reset. This changes the condition in the causal diagnosis instead of hiding the outer exception. The repeated control proves ownership before recovery from latest checkpoint on a topology that excludes the degraded link.

# Preserve evidence before restarting
dmesg -T | grep -iE 'NVRM|Xid|AER|NVLink|ECC'
nvidia-smi -q
dcgmi diag -r 3

# Find the exact signature in the complete log
rg -n -F -- "DCGM_FI_DEV_NVLINK_CRC_FLIT_ERROR counter incremented link degraded" <log-file>

Adapt the snippet to your framework. The same pattern holds for PyTorch Lightning, Hugging Face Trainer, DeepSpeed, Megatron-LM, and vLLM training wrappers. Where the wrapper exposes a config flag (for examplelr_scheduler_type in Trainer), prefer the flag over the imperative API to keep the schedule declarative and reproducible.

Select the traceback or open the failed terminal, then run Denpex locally to see the initiating rank, collateral failures, exact fix, and verification command without uploading the log.