[Bug 85064] modesetting driver plus DRI3 causes extremely slow scrolling with WebKitGTK+ in accelerated compositing mode

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=85064

--- Comment #37 from Dave Airlie <airlied at freedesktop.org> ---
00:46 < airlied> keithp: dri3/present question
00:46 -!- ofourdan [~ofourdan at 107-2.ar.fundp.ac.be] has quit [Ping timeout: 260
seconds]
00:46 < airlied> keithp: epiphany/webkit appears to be drawing offscreen
00:46 < keithp> a fine plan
00:46 < airlied> and currently -modeseting returned no crtc for that
00:46 -!- ofourdan [~ofourdan at 107-2.ar.fundp.ac.be] has joined #xorg-devel
00:46 < airlied> so we ended up throttling to the 1s fake crtc
00:47 < keithp> oh, 'offscreen' and not to a pixmap?
00:47 < airlied> yup offscreen not a pixmap
00:47 < keithp> wtf?
00:47 < airlied> I can say bong :)
00:47 < keithp> well, sucks to do something stupid?
00:47 < airlied> yes appears to be a window at +2000 or something
00:47 < keithp> and so what would they like us to do?
00:48 < airlied> "x = 2881, 
00:48 < airlied>     y = 0, width = 2910, height = 1783"
00:48 < airlied> well -amdgpu didn't hit the problem I think by accident, as it
alwasys picked the primary crtc no matter what
00:48 < airlied> if nothing else fit
00:48 < keithp> are they doing they're own compositing or something?
00:49 < airlied> it's one of those multi-process rendering things
00:49 < airlied> web browser and per-process web renderer
00:49 < keithp> sure, which is obviously a fine plan
00:49 < keithp> how are they capturing those pixels then?
00:49 < airlied> not sure, how they get them into the final image
00:49 < airlied> must be compositing them somehow I suppose
00:50 < keithp> I assume it's a deeply nested child window and they're doing
their own compositing
00:50 < keithp> So, they can't use a pixmap because GL sucks, I assume
00:50 < airlied> yeah most likely a GL suckage
00:50 < airlied> as they are defintely swapbuffersing
00:52 < airlied> but yeah I'd just think we need to standardise the response to
this behaviour :)
00:52 < keithp> I already did
00:52 < airlied> rather than luck of the driver maintainer draw
00:52 < keithp> anyone using DRI3 will get one frame per second
00:53 < airlied> so that's likely a big change from DRI2 behaviour
00:53 < keithp> DRI2 behaviour used to be unthrottled entirely
00:53 < keithp> you'd get infinite FPS
00:54 < keithp> which kinda sucked when the screen saver fired and your CPU/GPU
utilization went to 100%
00:54 < airlied> I suppose GLX specifies nothing useful either

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