CPU Usage going high during user operation

[kumararajas]

Adding to my experiments,
I have created a blank application, dragged up tablewidget and prepopulated about 30 rows. Built the app and ran it on my target.
It showed up the scroll bar. I dragged the scroll bar handle up and down continuously.
And I saw the CPU shooted up to 61%.

Is it the expected behaviour?

[kumararajas]

Any further thoughts?

Thanks,
Kumara

[SGaist]

The interest mailing list is followed by the Qt developers/maintainers.

You should also benchmark with QTableView and a custom model.

[kumararajas]

Yes I did!

That's where I have started up. I had QTableView with my own model, that was shooting up the CPU usage, at times, to 99% as well.
Then I started to dig in and found that simple application with scrollbar, sample Qt applications also take high CPU.

For example, slider example in Qt directory, cross compiled and ran it on the target. When I operate the scroll bar, CPU usage reaches 67% easily.

I am thinking if its a bug in scrollbar code?

[SGaist]

There might be something sub-optimal going on.

[kumararajas]

This is still an open point. Any thoughts on this?

Is it a bug in Qt that on scrolling, it consumes high cpu?

I also see a Qt bug report - https://bugreports.qt.io/browse/QTBUG-57550

[SGaist]

With 5.9 / 5.10 ?

[kumararajas]

@SGaist Sam! Neither of that. I am still on ancient age 4.8.7 :)

[SGaist]

Do you know at which points is start to slow down ?

[kumararajas]

@SGaist Just have a decently big project tree, about 50 branches, with 50 children each.
Just press and hold the down arrow in the scroll bar, we can observe that CPU % usage will constantly increment.

In Ubuntu, we can see that it is a gradual increment.

In case of AM335x, we can see that it shoots up to 60%.
One other operation - Just drag the scrollbar handle up and down continuously, Ubuntu can go up to 30%, AM335x can go to 80%.