Cinnamon notifications rendering performance issues

[alexkuz]

Distribution

Mint 21.3

Package version

6.0.4

Graphics hardware in use

No response

Frequency

Always

Bug description

This is the same issue as discussed in https://forums.linuxmint.com/viewtopic.php?t=403441, just wanted to share some findings regarding that.

The issue is that sometimes notifications list leads to a very laggy behaviour of the whole system, which is probably caused by some rendering loop.
I've noticed that it is happening when the notification list popup takes whole window height, causing each notification item to shrink in height.
Note that if more notifications added and there's not enough place even for shrinked items (so that there is overflow in scrollview), the issue is gone. It only happens in the edge case when gui still can fit all the items without scrolling.

I'm not sure on what level this is happening, certainly somewhere deeper than notification applet itself.

The performance hit may vary - for example, on 100% display scale I have much less (but still noticeable) impact, comparing to my default 150% scale. My guess that a specific display scale is not important though, the essential part is how easy it is to fit the list in current height.

Steps to reproduce

you can reproduce that by adding a bunch of notifications (the exact number depends on display resolution I guess)

for i in {0..8}; do notify-send -a "testapp" "test$i" "test$i"; done

Expected behavior

Notification list should be rendered fast enough with any popup size

Additional information

No response