[Buildroot] Raspberry Pi OpenGL/Qt5 10x slower than Raspbian

Frank Hunleth fhunleth at troodon-software.com
Thu Aug 4 17:09:52 UTC 2016


Hi Thomas,

On Thu, Aug 4, 2016 at 12:28 PM, Thomas Petazzoni
<thomas.petazzoni at free-electrons.com> wrote:
> Hello,
>
> On Thu, 4 Aug 2016 08:35:24 -0400, Frank Hunleth wrote:
>
>> > Change -Os by -O2 in the Buildroot configuration, by using
>> > BR2_OPTIMIZE_2. I even believe we should stop using BR2_OPTIMIZE_S by
>> > default, and switch to BR2_OPTIMIZE_2 instead.
>>
>> Done, but no luck for this particular issue. I have another piece of
>> code that differs in performance from Debian by 5% and is more CPU
>> bound. I'll try it on that too.
>
> Gaah.
>
>> > Also, are you sure it's really using OpenGL with the Buildroot build?
>>
>> On the Buildroot build, I've tried running the Qt application with
>> "-platform eglfs", but that seemed to be the default already. I'm not
>> sure how to check deeper than that.
>
> I guess if eglfs support has been built and you're able to use, it
> means that it's using the GPU.
>
>> > Under Raspbian, are you also running the eglfs build of Qt, or is it
>> > with X.org? I'm not sure Debian has an eglfs capable build of Qt5.
>>
>> You're right. On Raspbian, I'm running with X.org. I am naively
>> assuming that Qt5 w/ eglfs isn't 10x slower than Qt5 w/ X.org. I
>> really hope that's not the case.
>
> I also hope, but using X.org on one side and doing eglfs on the other
> side is really a very different configuration. I would also assume that
> there should not be a 10x difference between Qt5/X.org vs Qt5/eglfs,
> but I have never tested, so I don't know.

I started a Qt5/eglfs-only build on a Raspberry Pi early this morning.
I have no clue how long it will take to build, but I'll report back
when it's done.

> Which toolchain are you using ? Are you building everything optimized
> for ARMv6 (assuming you're using Rpi1) ?

When I first noticed the issue, I was using an ARMv6-optimized
toolchain built by crosstool-ng. Now I'm using the default one built
by Buildroot when using the raspberrypi_defconfig.

> But a 10x difference really feels like acceleration is not used at all.

I agree.

> You can also check the CPU consumption while running your Qt app to see
> what it looks like.

Will do. I think that the native Raspbian Qt5/eglfs-only build will be
telling. With any luck the build will complete successfully this
evening.

Thanks,
Frank


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