[Bug 99418] DRI3 Stuttering while scrolling in Chromium/Chrome with VBLANK off

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=99418

--- Comment #18 from lei.pero at gmail.com ---
(In reply to Michel Dänzer from comment #17)
> (In reply to lei.pero from comment #14)
> > It does happen on modesetting driver regardless of DRI version, strange.
> 
> The modesetting driver doesn't allow disabling DRI3 on the server side. You
> can always disable it on the client side though with the environment
> variable LIBGL_DRI3_DISABLE=1 .
> 
> The fps graph shows the same framerate in both videos, so the problem seems
> rather about animation timing. It might be related to the fact that DRI3
> allows triple buffering, and might be at least partially an application
> issue. It would be interesting though if it also happens with a non-AMD GPU.
> 
> BTW, is there any particular reason why you're disabling sync-to-vblank? It
> is the intended mechanism for smooth animation...

I didn't know that about modesetting driver, anyway, even with
LIBGL_DRI3_DISABLE=1 same thing happens.

I don't how to disable tripple buffering to test it and if it's possible, man
pages do not show anything about it. I've also tested on nouveau, same thing
happens, architecture is completely different with Intel C2D CPU @3.0GHz and
GT-210 (on this PC it's AMD FX-4100 CPU stock), both modesetting driver and
nouveau with DRI3 act the same, while nouveau with DRI2 works well same as
radeon with DRI2. If you have any idea where to look for further testing, I can
do it.

Yes, there are reasons, on some webpages (it is probably fault of page coding
or PC CPU power) CHromium/Firefox can't keep up with 85FPS, while drop happens,
when VBLANK is enabled, I'm getting less responsive mouse wheel (lag), while
with VBLANK disabled FPS drop is less severe, and there are is no input lag on
wheel or anything. That is main reason, among others that can be solved with
scripts (too alzy to type command when starting application without it = game
or something), also, videos do seem smoother (VLC, youtube etc.) with VBLANK
disables, so there are multiple reasons why I do it.

So, any way to disable tripple buffer? Or if you have idea what might be the
cause of the problem?

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