[c-nsp] troubleshooting SVI input drops on MSFC3

[barney gumbo]

I am seeing high input interface drops on an SVI interface on an MSFC3.  The
MSFC3 is installed in a 6503 chassis with Sup720.  The switch is running
hybird mode.

The traffic load has increased, and CPU is running high when the traffic
load increases.  I don't know why the SVI is showing increased traffic load
because normally I don't see traffic through the SVI, it all get's MLS
switched.  Something in the last week has caused traffic to be switched
through the SVI showing the high input drops.  The overal load of traffic
which should be routed (MLS switched) via the interface has not increased or
decreased; all of a sudden in the last week traffic is being (seemingly)
process switched through this SVI.

Where do I begin troubleshooting high interface drops on an SVI?