Nouveau - Nov 2018 - [Bug 108651] New: Screen flickering when using compositor with OpenGL backend

https://bugs.freedesktop.org/show_bug.cgi?id=108651

            Bug ID: 108651
           Summary: Screen flickering when using compositor with OpenGL
                    backend
           Product: Mesa
           Version: unspecified
          Hardware: All
                OS: Linux (All)
            Status: NEW
          Severity: normal
          Priority: medium
         Component: Drivers/DRI/nouveau
          Assignee: nouveau at lists.freedesktop.org
          Reporter: yshuiv7 at gmail.com
        QA Contact: nouveau at lists.freedesktop.org

Some users of both compton and nouveau have experienced screen flickering when
using the upgraded compton with GLX backend.

Nothing really changed in how compton uses OpenGL, so I suspect this could be a
driver bug.

For details, please go to: https://github.com/yshui/compton/issues/33

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--- Comment #1 from Ilia Mirkin <imirkin at alum.mit.edu> ---
How reproducible is this?

Is there an easy way for me, a non-compton user, to see these issues without
massive software installation? (Could I just run compton with windowmaker, for
example?)

What version of mesa did this work with? Or what was the change that
precipitates these issues?

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--- Comment #2 from Yuxuan Shui <yshuiv7 at gmail.com> ---
compton itself does not have lots of dependencies. Right now all the users
experienced this problem seems to be using the i3 window manager, I don't
know
if this is reproducible with windowmaker.

I don't know the mesa version they use, I will ask. But judging that they
are
all archlinux users, they are probably using mesa 18.2.4.

They started experiencing this issue when they upgraded their compton. One of
the reporters did a bisect (though he cannot reliably reproduce this problem)
and find out the bad commit seems to be
https://github.com/yshui/compton/commit/7af815a0aaaffc02e114e1d0adccb5f87dcc3548,
which touches nothing OpenGL related.

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On Mon, Nov 5, 2018 at 1:06 PM <bugzilla-daemon at freedesktop.org>
wrote:
>
> Comment # 2 on bug 108651 from Yuxuan Shui
>
> compton itself does not have lots of dependencies. Right now all the users
> experienced this problem seems to be using the i3 window manager, I
don't know
> if this is reproducible with windowmaker.
>
> I don't know the mesa version they use, I will ask. But judging that
they are
> all archlinux users, they are probably using mesa 18.2.4.
>
> They started experiencing this issue when they upgraded their compton. One
of
> the reporters did a bisect (though he cannot reliably reproduce this
problem)
> and find out the bad commit seems to be
>
https://github.com/yshui/compton/commit/7af815a0aaaffc02e114e1d0adccb5f87dcc3548,
> which touches nothing OpenGL related.
>
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https://bugs.freedesktop.org/show_bug.cgi?id=108651

--- Comment #3 from cj.wijtmans at gmail.com ---
unsubscribe
On Mon, Nov 5, 2018 at 1:06 PM <bugzilla-daemon at freedesktop.org>
wrote:
>
> Comment # 2 on bug 108651 from Yuxuan Shui
>
> compton itself does not have lots of dependencies. Right now all the users
> experienced this problem seems to be using the i3 window manager, I
don't know
> if this is reproducible with windowmaker.
>
> I don't know the mesa version they use, I will ask. But judging that
they are
> all archlinux users, they are probably using mesa 18.2.4.
>
> They started experiencing this issue when they upgraded their compton. One
of
> the reporters did a bisect (though he cannot reliably reproduce this
problem)
> and find out the bad commit seems to be
>
https://github.com/yshui/compton/commit/7af815a0aaaffc02e114e1d0adccb5f87dcc3548,
> which touches nothing OpenGL related.
>
> ________________________________
> You are receiving this mail because:
>
> You are the QA Contact for the bug.
> You are the assignee for the bug.
>
> _______________________________________________
> Nouveau mailing list
> Nouveau at lists.freedesktop.org
> https://lists.freedesktop.org/mailman/listinfo/nouveau
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--- Comment #4 from Yuxuan Shui <yshuiv7 at gmail.com> ---
They confirmed they are using mesa 18.2.4

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--- Comment #5 from John Lindgren <john at jlindgren.net> ---
This probably isn't specific to nouveau.  I am using Intel graphics
(modesetting driver) and I was also bitten by screen flickering in compton
after the switch to XCB (commits 43f3744fea07 and 7af815a0aaaf).

It is specific to DRI2.  With DRI3 or software rendering
(LIBGL_ALWAYS_SOFTWARE=1), the flickering goes away.

Looking at mesa source (src/glx/dri2.c), DRI2 seems to be incompatible with xcb
event processing due to usage of XESetWireToEvent()/XESetEventToWire(), which
hook into the traditional Xlib event processing.  Without Xlib in the loop,
DRI2 misses its Invalidate events and the result is that glXSwapBuffers()
doesn't work as expected.  (Take a look at src/glx/dri2_glx.c -
dri2XcbSwapBuffers() contains an explicit XSync() call to wait for Invalidate
events, which it never gets.)

One workaround I found is to change the following line in src/glx/dri2_glx.c:

   pdp->invalidateAvailable = (pdp->driMinor >= 3);

To this:

   pdp->invalidateAvailable = 0;

This causes mesa to think it's using an older X Server that doesn't send
Invalidate events and use some kind of internal fallback.  It's enough to
make
the flickering go away, but I don't know what other side effects it has.

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--- Comment #6 from Ilia Mirkin <imirkin at alum.mit.edu> ---
Note that by default, xf86-video-nouveau does not expose DRI3. There's a bit
of
incompatibility between EXA and DRI3, which I'm told is unfixable (without
major changes to EXA).

This can be forced by adding

Option "DRI" "3"

in the Driver section.

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--- Comment #7 from Yuxuan Shui <yshuiv7 at gmail.com> ---
So the problem is actually a incompatibility between using xcb event loop and
mesa DRI2.

It is hacked around in compton.

More details in bug 108705

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Yuxuan Shui <yshuiv7 at gmail.com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
         Depends on|                            |108705


Referenced Bugs:

https://bugs.freedesktop.org/show_bug.cgi?id=108705
[Bug 108705] GLX with DRI2 doesn't work properly when xcb is owning the
event
queue
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Yuxuan Shui <yshuiv7 at gmail.com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
         Depends on|                            |105132


Referenced Bugs:

https://bugs.freedesktop.org/show_bug.cgi?id=105132
[Bug 105132] glxSwapBuffers has no effect
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Bug 108651 depends on bug 105132, which changed state.

Bug 105132 Summary: glxSwapBuffers has no effect
https://bugs.freedesktop.org/show_bug.cgi?id=105132

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|NEW                         |RESOLVED
         Resolution|---                         |MOVED

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Bug 108651 depends on bug 108705, which changed state.

Bug 108705 Summary: GLX with DRI2 doesn't work properly when xcb is owning
the event queue
https://bugs.freedesktop.org/show_bug.cgi?id=108705

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|NEW                         |RESOLVED
         Resolution|---                         |MOVED

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GitLab Migration User <gitlab-migration at fdo.invalid> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|NEW                         |RESOLVED
         Resolution|---                         |MOVED

--- Comment #8 from GitLab Migration User <gitlab-migration at
fdo.invalid> ---
-- GitLab Migration Automatic Message --

This bug has been migrated to freedesktop.org's GitLab instance and has been
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You can subscribe and participate further through the new bug through this link
to our GitLab instance: https://gitlab.freedesktop.org/mesa/mesa/issues/1164.

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