Regarding the CPU Usage in arm board for an example of QTableView while scrolling

[Pradeep Kumar]

Hi,

I have a QTableview , i have used QStandardItemModel as a model , and added to QTableView, while scrolling . i have observed the CPU % gradually increases to 100%. same does not hold good in Desktop.

May i know what id the reason?.
Guidance will help me.
Thanks.

[VRonin]

this is due to paint being called frequently an in turn it having to query the model for data. fast scrolling brings my CPU usage to 10% (intel i7 3.6GHz). Do you use custom delegates or just pure Qt classes?

[Pradeep Kumar]

I am using Qt Classes , i am not using any custom delegates. Is their any difference in working in Desktop and Arm Board with the the same program?.

[SGaist]

Hi,

Depends on your Arm board, but it's likely less powerful than your desktop machine CPU/GPU wise. What board are you running your application on ?

[Pradeep Kumar]

I am using ARM 11. The application is running on ARM 11.

[SGaist]

That's an architecture. There are lots of ARM11 based processors/boards. What are you using exactly ?

[Pradeep Kumar]

Visiontek Pos device

[SGaist]

Can you give a link to the device description ?

[Pradeep Kumar]

The link is here , here is the link for the specifications of the device

[SGaist]

Ok, so you have have a single core 1GHz processor with 512MB of RAM.

What size is your model ?

[Pradeep Kumar]

@SGaist

The size is 320 , 240.

[SGaist]

I meant the data model

[Pradeep Kumar]

@SGaist

can u brief me up regarding the data model. what is it.?.

[jsulm]

@Pradeep-Kumar From your first post: "i have used QStandardItemModel as a model" - so I guess the question is how big is this model (how many elements does it contain)?

[Pradeep Kumar]

The standard item model data was having 3 columns and the rows values depends on DB values. it will increase as per the db values.

[SGaist]

Then what is the usual size of your database ?

[Pradeep Kumar]

Without Db also i tried the same, again i have observed the CPU % gradually increases to 100%. i didnt understand the behaviour. please guide me.

[SGaist]

Without any test case to run, it's pretty much impossible to help you get further. There's also no information about what else is running on your target or what your application does that might or might not be influenced by what happens in your GUI.

[Pradeep Kumar]

Their was some daemon process running, when i checked the application.

[SGaist]

Use top to see which is the processor hog: Likely your application but you have to verify to be sure.

After that confirmation, it would also be useful if you could describe precisely how you trigger that CPU load.

On a side note: which version of Qt are you using ? With which plugin ?

[Pradeep Kumar]

I will check the process bu using command top.
I am using Qt version 5.7.

  <After that confirmation, it would also be useful if you could describe precisely how you trigger that CPU load.>

I didnt get the above statement.

[SGaist]

After you confirmed that the CPU hog is indeed your application. It would be useful that you describe precisely what you do that makes the CPU go wild.

You didn't wrote which plugin you were using for your application. xcb ? wayland ? eglfs ?

[Pradeep Kumar]

Sorry about that missed to inform the plugin, I am using .xcb plugin.

[Pradeep Kumar]

Here is link of the screenshot of the cpu usage of the application
Application name is TableViewExample

https://postimg.org/image/awmpgc3wt/

[SGaist]

Which one of the QTableView example ? This one ?

[Pradeep Kumar]

Yes I have used QTableView , the example , and for the model i have used QStandardItemModel.
I will post the code.

m_pushButton = new QPushButton("Click To Get Data");

m_standardModel = new QStandardItemModel;
m_standardModel->setColumnCount(2);
m_standardModel->setRowCount(2000);
m_standardModel->setHorizontalHeaderItem(0,new QStandardItem("First Column"));
m_standardModel->setHorizontalHeaderItem(1,new QStandardItem("Second Column"));

m_tableview = new QTableView;
m_tableview->setVisible(false);

connect(m_pushButton,SIGNAL(clicked()),this,SLOT(getData()));

I have created Object in constructor Above lines of code.
And when i click the PushButton, i will be calling getData();

void getData()
{
int column_Count = 0;
int row_Count = 0;

QStandardItem *item,*item2;

for(row_Count=0;row_Count<=2000;row_Count++)
{
    item = new QStandardItem("Qt");
    m_standardModel->setItem(row_Count,column_Count,item);

    item2 = new QStandardItem("Company");
    m_standardModel->setItem(row_Count,column_Count+1,item2);
}

m_tableview->setModel(m_standardModel);
m_tableview->setVisible(true);

}

[SGaist]

Did you check at which number of rows the CPU starts to go under heavy load ?

[tham]

It is hard to tell the bottleneck without test, but I would like to share some experiences of QStandardItemModel vs custom model.

I have used QStandardItemModel and QTableView to create a rename tool before, the performance is quite horrible, even there are only several thousands of items(two column, original name vs name after changed), the speed could be very slow.

To alleviate the problem, I use QAbstractTableModel to replace QStandardItemModel, after that, I can handle one million data without lag for most of the rename operations(most of them can show the results after rename on the second column instantly).

In my custom model, I prefer QStringList(maybe std::vector<QString> would be faster) to store the data. I do not know the data structure underhood QStandardItemModel, but I guess it is some sort of tree like structure since QStandardItemModel need to be a universal model suit for every view, I suspect cache miss is the main reason why QStandardItemModel is so slow.

Because of this experiences, I only prefer QStandardItemModel if

1 : I know the size of the data are very small(less than two thousand rows)
2 : Running out of development fee(Customer do not want to pay for performance)