[Interest] Slow graphics effect (due to _dl_resolve_runtime_avx)

[Ch'Gans]

Hi there,

On my Linux computer (KUbuntu 16.10, AMD CPU), I'm having a big
performance problem with a very simple scene containing a single
ellipse with a drop shadow effect. When zooming in, the CPU usage goes
to 100% and the view takes ages to draw.
This is very simple to reproduce, no need for a complex scene:
m_scene = new QGraphicsScene(this);
auto item = m_graphicsScene->addEllipse(-10, -10, 20, 20);
item->setGraphicsEffect(new QGraphicsDropShadowEffect());
m_view->setScene(m_scene);

If i remove the drop shadow effect, everything runs fine.

I have tried this at work on a Windows computer with Intel CPU and i
don't have this problem.

I have run valgrind function profiler here, and it seems that my app
spend most of it's time in:
- QApplication::exec()/QGuiApplication::exec()
- _dl_runtime_resolv_avx/_dl_runtime_resolve_avx'2

Tested on KUbuntu with Qt 5.6.1 (as shipped by the distro), Qt 5.7
(online installer), i have the same problem. Uing QtCreator i have
tried to rebuild the app with a clean build environment and ran it
with a clean run environment, it didn't make any difference.

Tested on Windows with Qt 5.7 (online installer), i don't have any problem.

Has anyone seen this sort of behaviour, any clue on how to investigate
further and fix this?

Thanks,
Chris