CPU Usage going high during user operation

[kumararajas]

Adding to this,

I wrote a simple application, that has a tableview, and it contains 25 rows, prefilled with some data.

I ran this application on the embedded board.

On idle state, CPU usage was 0%, occasionally 1%.

When I scroll down the list slowly, I see that CPU was about 5%, which is a decent score.

When I scroll up and down the list, rigorously, I see that CPU usage is shooting to 50% or even more.

What is puzzling me is, this is a simple app, and is that Qt failed to optimize the implementation?

I am sure, I can do some tricks like, when move the slider, not to update the tableview and update only when slider is released. All those would definitely improve a bit.

But, these are all part of optimizations.

A simple tableview code, may be of 20 lines maximum, will end up having 100 lines of code for improving the performance. But, question is, why every Qt user has to implement this 100 lines of code to have efficient implementation? Why not Qt do such implementation by default?

I know I have poured off plenty of thoughts. (May be feeling pressure here? :P)

Please let me know your thoughts.

Thanks!

Kumara

[raven-worx]

@kumararajas
seems like this is something for the devs, so you should post it on the Qt dev mailing list
If you do so, please keep this post updated for others looking for the same issue.

[kumararajas]

Thanks for the response!

Can you please also share me the details about Qt dev mailing list?

Thanks!

[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%.