Created attachment 148903 [details]
Callgrind output from master
1. Open attachment 136239 [details]
2. Tools - Options - Writer - View: tick Smooth scroll
3. Scroll down the document by pressing Page Down on your keyboard
Only seen with gtk3, kde5 and win.
Arch Linux 64-bit
Build ID: 5408f0731b9cd8be0e1b7aa5145b825337baad84
CPU threads: 8; OS: Linux 4.20; UI render: default; VCL: gtk3;
Locale: fi-FI (fi_FI.UTF-8); UI-Language: en-US
Built on 5 February 2019
Version: 220.127.116.11.alpha0+ (x64)
Build ID: 573a473275ad7c76d0cada9b7e73d4923e7a79d5
CPU threads: 4; OS: Windows 10.0; UI render: default; VCL: win;
TinderBox: Win-x86_64@42, Branch:master, Time: 2019-02-03_01:22:10
Locale: fi-FI (fi_FI); UI-Language: en-US
Wait, does smooth scroll even respond to PgDn/PgUp or CursorDn/CursorUp? All of which relocate the edit cursor. Yes--but the edit cursor redraw seems to come after some amount of view scroll. That redraw/reposition seems to cause a pause in smooth scroll.
Conversely smooth scroll responds cleanly to the ScrollBar control which does not relocate the edit cursor, just the views of the canvas.