With an on-premises data gateway, what report processing occurs where?

Hi

I'm curious as to what infrastructure is used for processing what parts of a report data refresh when an on-premises data gateway is used for part of the data source collection in both a Power BI Pro and Premium licenced workspace setting?

For example if I have a report that pulls data from an on-premises database server, what happens where?

When I monitor my gateway resources, network seems to correlate pretty closely to the actual pulling of data which might take less than 5 minutes but even after that drops close to zero, CPU will continue with high utilisation for quite some time (sometimes over an hour) so I tend to think my gateway is doing more than just pulling data, compressing it and sending it to the shared Power BI Pro infrastructure. Even after my gateway goes quiet I see in my PBI service that the dataset is still refreshing for quite some time afterwards so I'm unsure what is actually going on.

Also when I am viewing a report in my PBI Service, if I click on a filter that has a measure with a heavy DAX component the refresh circle can spin for a while - is that my browser or the PBI shared infrastructre doing the data churning at that point?

Many Thanks