[Development] why Qt app performance low on qpa eglfs or wayland

[Sean Harmer]

On 5 Sep 2014, at 09:39, Nancy Zou <Nancy.Zou at csr.com> wrote:

> Hi Millan
>> You should answer this question yourself and present the results to us. Only you have your specific software/hardware combination setup properly.
> 
> I suspect Qt wati for vsyc somewhere because the normal opengl example only cost 14ms (1 vsync) and Qt example openglwindow need 28 ms( just 2 vysnc) 
> I think it's strange a simple opengl example run such low fps. 
> My fb driver already wait for vsync once in eglSwapBuffers. So Qt don't need wait it. So I want to find out where qt hung. Whether Qt wait for some events somewhere?

Qt QPA plugins do the waiting precisely by calling eglSwapBuffers. You can control the swap interval by means of QSurfaceFormat::setSwapInterval(). Pass in a value of 0 to disable any sync, -1 to use adaptive sync (if your driver supports it), any other positive integer for that number of syncs.

Also make sure the QPA has the correct refresh rate for your screen.

Cheers,

Sean

> 
>> Try Linux' `perf top` e.g. or run your application via `perf record --call-graph=dwarf yourapp`. Then do a `perf report` and take a look at the results. Remember to compile your application and all  important dependencies (esp. Qt) in release mode with debug symbols, i.e. at least use the compile flags `-O2 -g`.
> 
> I have done this in qmake.
> 
> 
> Thank you
> 
> Best Regards
> Nancy 
> 
> 
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