Catalyst 3850: output drops, and SVI vs. routed port performance

My NMS just lit up with 7M output drops on a 1Gbps L2 physical interface, on a WS-C3850-24XS running Denali 16.3.6.

Netflow shows a spike on egress traffic for sure. But it's a very brief spike to/from a single source/dest. Netflow also shows minimal traffic egressing that physical interface, aside from this one conversation.

7M drops seems ridiculous when there's nearly all of 1Gbps ASIC-driven L2 bandwidth, end-to-end, between these two endpoints.

Then I realized the endpoints are on different vlans. They are routing through an SVI on the 3850, even though the SVI reports no issues.

The datasheet shows 454Mpps forwarding capacity for the WS-C3850-24XS and NMS confirms we are several orders of magnitude lower than that across the data plane. Sure, it is passing a bunch of traffic, but best I can tell it's well within spec.

Got me wondering if SVIs are routed in software vs. ASIC?

Couldn't find anything definitive online, at least for Catalyst. Found this for ISR, but not sure if that applies here.