This document is relevant for: Inf2, Trn1, Trn2, Trn3

NCC_EVRF066#

Error message: NKI kernel ‘<kernel-name>’ is configured with LNC=<kernel-lnc>, but neuronx-cc is using LNC=<compiler-lnc>.

This error occurs when a NKI kernel and neuronx-cc use different Logical Neuron Core (LNC) configuration values (degrees). LNC degree is a global compilation property of a model compute-graph, so all NKI kernels embedded in a model must use the same LNC degree as neuronx-cc.

For more information on how to configure the LNC degree of NKI kernels, see: LNC Overview.

Common causes#

Not explicitly setting the LNC degree for NKI kernels.

kernel(...)  # Kernel implicitly defaults to LNC=1; neuronx-cc defaults to LNC=2 on Trn2 and later.

Using the launch-grid bracket syntax, such as kernel[1](...), to set an LNC degree that differs from the LNC degree used by neuronx-cc. This syntax is being deprecated.
```
kernel[1](...)  # Kernel explicitly uses LNC=1; neuronx-cc defaults to LNC=2 on Trn2 and later.
```

Overriding the --lnc option passed to neuronx-cc, for example through NEURON_CC_FLAGS, with an LNC degree that differs from the NKI kernel LNC degree.

export NEURON_LOGICAL_NC_CONFIG=2  # Set kernel LNC=2.
export NEURON_CC_FLAGS="--lnc=1"

kernel(...)  # Kernel explicitly uses LNC=2; neuronx-cc is overridden to LNC=1.

Resolution#

Explicitly set the NEURON_LOGICAL_NC_CONFIG environment variable to the desired LNC degree so that neuronx-cc and all NKI kernels use the same LNC degree. ML frameworks generally pass the value of this environment variable to neuronx-cc through its --lnc flag.
Remove any launch-grid bracket syntax from the NKI kernel call site, such as kernel[1](...).
Remove any conflicting --lnc overrides, such as one set through NEURON_CC_FLAGS.

LNC=1 example#

Before:

kernel(...)  # Kernel implicitly uses LNC=1; neuronx-cc defaults to LNC=2 on Trn2 and later.

After:

export NEURON_LOGICAL_NC_CONFIG=1
kernel(...)  # Kernel and neuronx-cc both use LNC=1.

LNC=2 example#