[Mesa-dev] Performance regression on Tegra/GK20A since commit 363b53f00069

[Alexandre Courbot]

Hi Pekka,

On 11/19/2014 04:34 PM, Pekka Paalanen wrote:
> On Wed, 19 Nov 2014 15:32:38 +0900
> Alexandre Courbot <acourbot at nvidia.com> wrote:
>
>> Some more information: CPU usage of the EGL app (glmark2 here) is much
>> higher when this patch is applied, which I presume is what triggers the
>> frame skips.
>>
>> On 11/19/2014 03:05 PM, Alexandre Courbot wrote:
>>> Hi guys,
>>>
>>> I am seeing a severe performance regression (lots frame drops when
>>> running EGL apps in Weston) on Tegra/GK20A since the following commit:
>>>
>>> commit 363b53f00069af718f64cf047f19ad5681a8bf6d
>>> Author: Marek Olšák <marek.olsak at amd.com>
>>> Date:   Sat Nov 1 14:31:09 2014 +0100
>>>
>>>       egl: remove egl_gallium from the loader
>>>
>>> Reverting said commit on top of master brings the expected performance
>>> back. I am not knowledgeable enough about Mesa to speculate about the
>>> reason, but could we try to investigate why this happens and how we
>>> could fix this?
>
> Hi,
>
> that sounds like you used to get egl_gallium as the EGL driver, and
> after that patch you get egl_dri2. These two have separate Wayland
> platform implementations (and probably all other platforms as well?). I
> think that might be a lead for investigation. EGL debug environment
> variable (EGL_LOG_LEVEL=debug) should confirm which EGL driver gets
> loaded. You can force the EGL driver with e.g. EGL_DRIVER=egl_dri2.

You are spot on, EGL_LOG_LEVEL revealed that I was using the egl_gallium 
driver while this patch makes Wayland applications use egl_dri2. If I 
set EGL_DRIVER=egl_gallium things go back to the expected behavior.

>
> Note, that there are two different EGL platforms in play: DRM/GBM for
> Weston, and Wayland for the app. Have you confirmed the problem is in
> the app side? That is, does Weston itself run smoothly?

Weston seems to be fine, and since setting EGL_DRIVER=egl_gallium after 
starting it brings things back to the previous behavior I believe we can 
consider it is not part of this problem.

>
> FYI, I've been slowly working on https://github.com/ppaalanen/wesgr but
> the Weston patches are not upstream yet, and I'm in the process of
> updating them currently. I hope this tool might give some indication
> whether the skips/stalls happen in Weston or not.
>
> You say "frame drops", how do you see that? Only on screen, or also in
> the app performance profile? How's the average framerate for the app?

Looking at it again this is actually quite interesting. The misbehaving 
app is glmark2, and what happens is that despite working nicely 
otherwise, a given frame sometimes remain displayed for up to half a 
second. Now looking at the framerates reported by glmark2, I noticed 
that while they are capped at 60fps when using the gallium driver, the 
numbers are much higher when using dri2 (which is nice!). Excepted when 
these "stuck frames" happen, then the reported framerate drops 
dramatically, indicating that the app itself is also blocked by this.

Interestingly, if I run weston-simple-egl with dri2, the framerate is 
again capped at 60fps, so this may be something specific to glmark2.

Also, and I cannot explain why, but if there is other activity happening 
in Weston (e.g. another egl application, even another instance of 
glmark2 itself), the issue seems to not manifest itself.

Just for my education, is the egl_gallium driver going to be removed? 
What are egl_gallium and egl_dri2 doing differently?

Thanks,
Alex.