This, yes. Also, if you're processing discrete items in any measurable way (downloading kilobytes, ingesting database rows, querying servers...) that takes longer than one second flat, display that to users. "Processing record 1/1,000,000... Processing record 2/1,000,000..." gives a positive sense of progress. Even if you don't actually know the final total in advance, you should still display whatever you've got.

As a bonus, this can occasionally be useful for bug squashing. "I've been waiting for hours and it's only up to row 5681" when you know for a fact that there's <2000 rows is a lot more informative than "My report won't finish."