[Mesa-dev] very strange intermittent frame-dropping

[Eero Tamminen]

Hi,

On 04.04.2017 09:23, Luke Kenneth Casson Leighton wrote:
> https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=848895
>
> there's a really strange and comprehensively cross-application
> intermittent bug that's only occurring on opengl-based applications,
> that's been introduced some time in the past year.  to be absolutely
> honest nobody's even sure it's actually opengl-related or whether it's
> x11 related, but it's so weird that it's really hard to pin down.
>
> the above bugreport on debian with chromium-browser is *just one* of
> the occurrences, but it occurs with glxgears, openscad and a whole
> stack of other applications.
>
> the simplest 100% guaranteed way discovered so far to reproduce the issue is:
>
> * install debian / testing
> * install fvwm2
> * set up fvwm2 to use "wireframe" for "resize window"
> * run glxgears
> * go ahead and resize the glxgears window with a mouse
>
> that is *guaranteed* to result in glxgears "freezing".  the only known
> guaranteed way to "recover" it is to switch to text console
> (ctrl-alt-f1) followed by switching back to X11 (ctrl-alt-f7).

That's pretty good clue.


> there are various teams trying to "fix" this bug, believing it to be
> the fault of their application.  this includes the chromium-browser
> team.  what they've managed to do so far is to simply... avoid *most*
> circumstances under which the lock-up occurs... but all that happens
> is that the processor running the application goes into multi-tasking
> meltdown... *and then still* gets a lock-up.
>
> it doesn't matter what underlying hardware is used: intel graphics,
> nvidia, ATI.  it doesn't even matter if you use optirun: that *still*
> results in a lockup although there you get a rather useful error
> message indicating that the GPU is trying to do its job, but reports
> constantly that the frame had to be dropped.
>
> anyway, apologies: nobody whose applications are affected by this
> really has a clue where the *actual* bug is so i am escalating it down
> the chain of library dependencies, making people aware.  it could be
> X11, it could be mesa, we just don't know.

Does it happen only with the old, non-compositing window managers like 
FVWM2, or also with something newer?

Does DRI2 vs. DRI3 have any effect on it?


	- Eero