[Bug 73528] Deferred lighting in Second Life causes system hiccups and screen flickering

[bugzilla-daemon@freedesktop.org]

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https://bugs.freedesktop.org/show_bug.cgi?id=73528

MirceaKitsune <sonichedgehog_hyperblast00@yahoo.com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Priority|medium                      |high
            Version|git                         |10.3

--- Comment #16 from MirceaKitsune <sonichedgehog_hyperblast00@yahoo.com> ---
Okay, I just found an important clue: The issue is not limited to Second Life
alone! I just tried to enable shaders in the open-source racing game Stuntrally
(Vdrift Ogre) and got the exact same problem. The machine would freeze, the
screen would flicker (monitor going in standby), but in this case it would
unfreeze after a few seconds so I managed to turn shaders off.

Additionally, I did more tests in Second Life several days ago, and found
something interesting: If I look at the ground so barely anything is rendered,
the shaders work perfectly well. But if the sky or too much detail come into
view, it only takes a few seconds until the GPU suddenly hiccups and I can
barely re-stabilize the system.

I'm unclear whether this is a coincidence. But when the problem takes place,
the fan on my video card is running at maximum speed, indicating the Radeon DPM
module is stressing the card out. Note that the freezes existed before DPM was
supported by the free driver, and came after a MESA update alone.

My humble impression is that some shaders either create an infinite loop on the
GPU due to a compilation bug, either they're so unoptimized that they flood the
GPU with data it can't handle. It does seem to be triggered by specific objects
coming into view... but I can't tell if that's because of the model complexity
(high polygon count) or because they contain a "sick" shader which the video
card attempts to render.

Since this has been around for an year, and I gathered a few clues already,
please allow me to set it to "high" priority to bring more awareness. I'm
around and watching this, so I can do more tests... as long as it's nothing
that would risk breaking my system (like changing system drivers).

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