Slow performance and large memory usage with QTableView in Qt 5.15

KaoN

@JonB Thank you for your suggest, but after several tries, I thought I might find a bug with Qt 5.15 at least.
Same code works fine with 5.9.9, fast and smooth, but fail to perform the same when I using the latest release, with memory usage nor CPU consumption.

Should I open a bug for that ?

Christian Ehrlicher

Your testapp opens instantly here on linux with 5.15.0 / 64 bit

KaoN

@Christian-Ehrlicher thx for testing it for me
, then it might be a bug related to windows only？

Christian Ehrlicher

I also don't have problems with your example with Qt5.15.0 / MinGW64 on Windows 7. Please make sure that you have a clean build dir, maybe even create a new clean project to test it.

KaoN

@Christian-Ehrlicher hmm..that's wierd, I did a clean project and using both MSVC and MinGW64 , same bad performance on Windows 10 1909, fine with 5.9.9

KaoN

After rebooting my pc.. everything works fine....
still cant get why...

Christian Ehrlicher

@KaoN Then please mark this topic as solved

KaoN

@Christian-Ehrlicher done, but can't figure out what made that 'bug' happen

JonB

@KaoN Windows

KaoN

After hibernating my desktop for a night, it slows again.. and...reboot does not work anymore..TT

KaoN

I deploy two version of the testapp to another laptop, win10 20H2, 5.9 perform good and 5.15 with no luck

JKSH

@KaoN said in Slow performance and large memory usage with QTableView in Qt 5.15:

After hibernating my desktop for a night, it slows again.. and...reboot does not work anymore..TT

Are you running out of RAM? I'm guessing that the slowdown happens when your PC is busy transferring data between your physical RAM and your Pagefile. That is a very slow process.

Run Resource Monitor (https://www.thewindowsclub.com/use-resource-monitor-windows-10 ) and see what is using up all your memory and your disk I/O.

KaoN

@JKSH Thank you for your reply, but my desktop has 64GB memory, I don't think it cause the problem.
The question is with 5.9.9, it works fine, with only 10MB memory consumption.

JKSH

@KaoN said in Slow performance and large memory usage with QTableView in Qt 5.15:

The question is with 5.9.9, it works fine, with only 10MB memory consumption.

It's possible that the implementation of QTableView changed between Qt 5.9 and Qt 5.15 which provides better performance in some use-cases but worse performance in other use-cases.

Do you have Qt 5.12 LTS installed? How does it perform with that version?

You can post your minimal test code and provide instructions on how to cause the slowdown to https://bugreports.qt.io/. However, it is still not clear to me whether it is a bug/regression or not.

KaoN

@JKSH Yes, I tried 5.12.7, slow too.
Bug is reported with minimal code: https://bugreports.qt.io/browse/QTBUG-86069?filter=16824

KaoN

@JKSH The weird thing is that I did get good performance after I reboot my desktop, but it did not always working..actually, it only works once.

Christian Ehrlicher

I'm pretty sure your Qt example has nothing to do with this.

J.Hilk

@KaoN have you done a full hard shutdown or only the soft one that comes when opening the start menu ?

hit win + r

then type:
shutdown /s /f /t 0

KaoN

@J-Hilk It did help to get everything work well again...but could you plz explain a bit, is it a system bug?

J.Hilk

@KaoN Microsoft made this change a while ago when the UWP, Windows for mobile/tablet was a thing and windows required faster reboots/boots/wakeups

As a result all modern Windows system have a "soft reboot /shutdown" these days

Usually you don't notice this, until some day, fundamental stuff starts behaving strangely.

I for once managed it (with Qt no less) to get my bluetooth driver in an undefined state, so nothing, bluetooth worked anymore, and a reboot did not fix it, because the normal reboot does not reinitialize and clear everything. That's how I learned about it.

Your case, smells like a bug hard to tell if Qt is at fault or not.
Have you tried updating your windows ? My Bluetooth story fixed itself with a windows update.

And have you tried it on a 2nd, different windows pc ?

If yes, and behavior is the same (in both cases) than it may be a Qt issue