Start up time and FPS problem using QT5 with different version of kernel

[qiangyu]

Hello,

I'm using IMX6Q Sabre Lite to run a QT5 demo, but there are two problems:

1. the start up time of the demo on 3.0.35 kernel is 3s slower than on 3.10.17 kernel
2. the FPS periodically drops using a 3.10.17 graphic stack while it remains 60 using a 3.5.7 graphic stack

The start up time diffs only on the call of

QGuiApplication app(argc, argv);

Some info about my platform:

IMX6Q Sabre Lite

QT5.2.1 & QT5.3.0

Buildroot

LVDS 1280x480

I've test many combination of kernel version and graphic stack, here is my conclusion:

1. the start up time only depends on the kernel version, not the graphic stack. Because the same graphic stack (including kernel part) with different kernel version will cause the problem; the same kernel (not the GPU driver part) with different graphic stack (including kernel part) won't cause the problem.
2. the FPS mainly depends on the graphic stack, kernel version only affects the drop amount. The 3.10.17 graphic stack drop more on 3.10.17 kernel while drop less on 3.0.35 kernel.

Does any one have the same problem?

Regards,

Qiang

[qiangyu]

Some progress:

the slow start up time of QT on 3.0.35 kernel is because the slow close time of /dev/input/event* device files.

It takes 0.3s for each of them in 3.0.35 kernel.