[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 #33 from lei.pero at gmail.com ---
(In reply to Michel Dänzer from comment #32)
> (In reply to lei.pero from comment #31)
> > It's still odd behaviour, in both cases Chrome caps FPS to refresh rate (this
> > case 85FPS),
> 
> Sounds like Chrome just has its own framerate throttling which works
> independently from sync-to-vblank.
> 
> 
> > but using DRI3 using mutter/clutter, for some reason it creates
> > continuous stutters, even tho FPS is the same and all other parameters are
> > equal. It really looks (when viewed live) as if FPS is not equal to refresh
> > rate.
> 
> It's possible that the mutter framerate doesn't match the refresh rate (you
> can check by setting GALLIUM_HUD=fps for the mutter process), but it's also
> possible it's simply due to unfortunate interaction between the Chrome and
> mutter frame timings.
> 
> 
> > [...] it is still probably mutter/clutter configuration problem in the code
> > (since it happens only there), it doesn't follow configuration in .drirc as
> > other WM's.
> 
> Not really. By setting vblank_mode=0, you're forcing mutter to run in a way
> it doesn't intend. If doing so breaks something, that can hardly be
> considered a mutter bug, and you get to keep all the pieces. :)

You might be very right about unfortunate interaction between Chrome (and
Chromium) and mutter frame timings, since I did tried "CLUTTER_DEFAULT_FPS=85"
(and 84) env. value and it made 0 difference.

Yeah, but by setting 1 and using any other WM results in Chromium/Chrome being
VSYNC-ed, or at least it looks like it is, there's no tear line and picture is
smooth as it can be (while on mutter/clutter there's tear line), so for the
sake of standardisation i would call it mutter/clutter configuration bug that
will probably stay unresolved, plus it doesn't explain DRI2 behavior that
follows same standard :).

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