[Bug 103544] Graphical glitches r600 in game this war of mine linux native

[Bug 103544] Graphical glitches r600 in game this war of mine linux native

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https://bugs.freedesktop.org/show_bug.cgi?id=103544

            Bug ID: 103544
           Summary: Graphical glitches r600 in game this war of mine linux
                    native
           Product: Mesa
           Version: 17.3
          Hardware: x86-64 (AMD64)
                OS: Linux (All)
            Status: NEW
          Severity: normal
          Priority: medium
         Component: Drivers/Gallium/r600
          Assignee: dri-devel@lists.freedesktop.org
          Reporter: shpalikvitalik@gmail.com
        QA Contact: dri-devel@lists.freedesktop.org

Created attachment 135209
  --> https://bugs.freedesktop.org/attachment.cgi?id=135209&action=edit
black artifacts

the problem with artifacts is observed in mesa 17.2 mesa 17.3. When the version
is rolled back to 17.0.5 the problem disappears and the game works without
artifacts.
I enclose the screenshots:

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[Bug 103544] Graphical glitches r600 in game this war of mine linux native

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https://bugs.freedesktop.org/show_bug.cgi?id=103544

--- Comment #1 from Emil Velikov <emil.l.velikov@gmail.com> ---
Vitalii can you bisect Mesa to the commit that broke the game? There aren't
many developer working on r600 - so this would be greatly beneficial.

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[Bug 103544] Graphical glitches r600 in game this war of mine linux native

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https://bugs.freedesktop.org/show_bug.cgi?id=103544

--- Comment #2 from Vitalii <shpalikvitalik@gmail.com> ---
tell me how and what to do and I'll try

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[Bug 103544] Graphical glitches r600 in game this war of mine linux native

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https://bugs.freedesktop.org/show_bug.cgi?id=103544

--- Comment #3 from Vitalii <shpalikvitalik@gmail.com> ---
(In reply to Emil Velikov from comment #1)
> Vitalii can you bisect Mesa to the commit that broke the game? There aren't
> many developer working on r600 - so this would be greatly beneficial.

tell me how and what to do and I'll try

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[Bug 103544] Graphical glitches r600 in game this war of mine linux native

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https://bugs.freedesktop.org/show_bug.cgi?id=103544

--- Comment #4 from Roland Scheidegger <sroland@vmware.com> ---
(In reply to Vitalii from comment #3)
> (In reply to Emil Velikov from comment #1)
> > Vitalii can you bisect Mesa to the commit that broke the game? There aren't
> > many developer working on r600 - so this would be greatly beneficial.
> 
> tell me how and what to do and I'll try

git bisect is easy, albeit building 32bit mesa on a 64bit distro might be
somewhere from challenging to near impossible depending on the distro...
You just do
git bisect start (probably on mesa master branch, but 17.2 branch should work
too)
git bisect good <sha id of a commit where things are working)
git bisect bad <sha id of a commit where things are broken)
build mesa, test (make sure testing really uses the newly compiled driver...)
git bisect good (or bad), build, test, rinse and repeat...

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[Bug 103544] Graphical glitches r600 in game this war of mine linux native

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https://bugs.freedesktop.org/show_bug.cgi?id=103544

--- Comment #5 from Roland Scheidegger <sroland@vmware.com> ---
I've actually got that game myself here.
So I did the bisect and the winner is:
ce7a045feeef8cad155f1c9aa07f166e146e3d00 is the first bad commit
commit ce7a045feeef8cad155f1c9aa07f166e146e3d00
Author: Ilia Mirkin <imirkin@alum.mit.edu>
Date:   Mon Jan 23 20:53:50 2017 -0500

    r600g: use ieee variants of multiplication instructions

    This matches the behavior of most other drivers, including nouveau,
    radeonsi, and i965.

    Signed-off-by: Ilia Mirkin <imirkin@alum.mit.edu>
    Reviewed-by: Nicolai Hähnle <nicolai.haehnle@amd.com>

Looks like some numerical issue then, albeit I don't know if the game is at
fault here.

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[Bug 103544] Graphical glitches r600 in game this war of mine linux native

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https://bugs.freedesktop.org/show_bug.cgi?id=103544

--- Comment #6 from Ilia Mirkin <imirkin@alum.mit.edu> ---
(In reply to Roland Scheidegger from comment #5)
> I've actually got that game myself here.
> So I did the bisect and the winner is:
> ce7a045feeef8cad155f1c9aa07f166e146e3d00 is the first bad commit
> commit ce7a045feeef8cad155f1c9aa07f166e146e3d00
> Author: Ilia Mirkin <imirkin@alum.mit.edu>
> Date:   Mon Jan 23 20:53:50 2017 -0500
> 
>     r600g: use ieee variants of multiplication instructions
>     
>     This matches the behavior of most other drivers, including nouveau,
>     radeonsi, and i965.
>     
>     Signed-off-by: Ilia Mirkin <imirkin@alum.mit.edu>
>     Reviewed-by: Nicolai Hähnle <nicolai.haehnle@amd.com>
> 
> Looks like some numerical issue then, albeit I don't know if the game is at
> fault here.

Apologies for the trouble.

The main difference between IEEE and non-IEEE is whether 0 * infinity = 0 or
NaN. IEEE makes it mean NaN. DX9 behavior is 0. I added a flag to be used by
st/nine to enable the DX9 behavior optionally, but leave the IEEE behavior for
GLSL. (There was some additional desire to expose that in a GL ext for WINE to
use, but it got shot down pretty quickly.)

Perhaps there are other changes from using the IEEE instruction variants, e.g.
denorms, which would be undesirable. I was never too familiar with the R600
ISA.

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[Bug 103544] Graphical glitches r600 in game this war of mine linux native

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https://bugs.freedesktop.org/show_bug.cgi?id=103544

--- Comment #7 from Roland Scheidegger <sroland@vmware.com> ---
(In reply to Ilia Mirkin from comment #6)
> The main difference between IEEE and non-IEEE is whether 0 * infinity = 0 or
> NaN. IEEE makes it mean NaN. DX9 behavior is 0. I added a flag to be used by
> st/nine to enable the DX9 behavior optionally, but leave the IEEE behavior
> for GLSL. (There was some additional desire to expose that in a GL ext for
> WINE to use, but it got shot down pretty quickly.)
> 
> Perhaps there are other changes from using the IEEE instruction variants,
> e.g. denorms, which would be undesirable. I was never too familiar with the
> R600 ISA.

I don't think these chips can do denorms at all.
I quickly looked at some trace, and indeed it looks like NaNs popping up in
some RT (which has a rgba16f format), and in that case it will then show as
black in the final output later.
I could not figure out what fragment shader is responsible for it, the NaNs are
always surrounded by pixels which are all black (hence making them
indistinguishable in qapitrace visually), plus that texture which gets the NaNs
is also blitted to from other textures via glBlitFramebuffer, which also
already has NaNs and so on, and I didn't invest all that much time...
I guess though the question is why other mesa drivers render it correctly and
how they avoid the NaNs if they also use ieee conformant behavior (if they
actually render it correctly...).

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[Bug 103544] Graphical glitches r600 in game this war of mine linux native

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https://bugs.freedesktop.org/show_bug.cgi?id=103544

--- Comment #8 from Ilia Mirkin <imirkin@alum.mit.edu> ---
(In reply to Roland Scheidegger from comment #7)
> I guess though the question is why other mesa drivers render it correctly
> and how they avoid the NaNs if they also use ieee conformant behavior (if
> they actually render it correctly...).

If you can get me a trace, I can have a look to see what happens with nouveau.

There's additional implications from having NaN's in RT outputs, i.e. what
happens in blending functions. I believe that nouveau configures the GPU for
the "zero wins" style of multiplication in the blending unit. And separately,
same thing for color clamps (I believe NVIDIA hw maps NaN -> 0 unconditionally
for that case).

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[Bug 103544] Graphical glitches r600 in game this war of mine linux native

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https://bugs.freedesktop.org/show_bug.cgi?id=103544

--- Comment #9 from Ilia Mirkin <imirkin@alum.mit.edu> ---
Created attachment 135237
  --> https://bugs.freedesktop.org/attachment.cgi?id=135237&action=edit
enable simple_float logic for blending

Entirely untested (not even compiled) patch to force blending to be 0*NaN=0.
Looks like radeonsi sets this bit, so it's not completely crazy.

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[Bug 103544] Graphical glitches r600 in game this war of mine linux native

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https://bugs.freedesktop.org/show_bug.cgi?id=103544

--- Comment #10 from Ilia Mirkin <imirkin@alum.mit.edu> ---
(In reply to Ilia Mirkin from comment #9)
> Created attachment 135237 [details] [review]
> enable simple_float logic for blending
> 
> Entirely untested (not even compiled) patch to force blending to be 0*NaN=0.
> Looks like radeonsi sets this bit, so it's not completely crazy.

Note that it looks like SIMPLE_FLOAT merely makes an optimization which allows
a GL_ZERO factor to cause a 0 to result... sometimes. But it could be enough
here. If an infinity or NaN makes it into a dest buffer, without this it will
ruin any future blending done, even if there's an attempt to override the
destination value.

Patch is available at https://patchwork.freedesktop.org/patch/186599/ (although
I'll have to rework the description)

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[Bug 103544] Graphical glitches r600 in game this war of mine linux native

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https://bugs.freedesktop.org/show_bug.cgi?id=103544

--- Comment #11 from Roland Scheidegger <sroland@vmware.com> ---
(In reply to Ilia Mirkin from comment #10)
> Patch is available at https://patchwork.freedesktop.org/patch/186599/
> (although I'll have to rework the description)

Doesn't help, everything looks the same.
FWIW I (accidentally...) also tested without float rt support (got really
confused first with the results...), and there's still corruption when the game
uses ordinary (gl_rgba) rt. I'm not sure the rendering is otherwise identical,
but at least SOME corruption disappears (in particular, the black boxes),
whereas other corruption remains exactly the same (some vertical stripes
sometimes, and the fires still are black in the interior).

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[Bug 103544] Graphical glitches r600 in game this war of mine linux native

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https://bugs.freedesktop.org/show_bug.cgi?id=103544

--- Comment #12 from Roland Scheidegger <sroland@vmware.com> ---
Here's a apitrace for this (1GB, of course the corruption is only seen towards
the end...), should be available a week (?):
https://we.tl/EanuxRG7Yf

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[Bug 103544] Graphical glitches r600 in game this war of mine linux native

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https://bugs.freedesktop.org/show_bug.cgi?id=103544

--- Comment #13 from Ilia Mirkin <imirkin@alum.mit.edu> ---
(In reply to Roland Scheidegger from comment #12)
> Here's a apitrace for this (1GB, of course the corruption is only seen
> towards the end...), should be available a week (?):
> https://we.tl/EanuxRG7Yf

Well, this all replays fine with nouveau, even if I remove the blending config
which makes 0*nan=0. At least I couldn't see any artifacts.

So this all points to ... sadness. Can you check if you still see artifacts
with nosb?

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[Bug 103544] Graphical glitches r600 in game this war of mine linux native

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https://bugs.freedesktop.org/show_bug.cgi?id=103544

--- Comment #14 from Roland Scheidegger <sroland@vmware.com> ---
(In reply to Ilia Mirkin from comment #13)
> (In reply to Roland Scheidegger from comment #12)
> > Here's a apitrace for this (1GB, of course the corruption is only seen
> > towards the end...), should be available a week (?):
> > https://we.tl/EanuxRG7Yf
> 
> Well, this all replays fine with nouveau, even if I remove the blending
> config which makes 0*nan=0. At least I couldn't see any artifacts.
> 
> So this all points to ... sadness. Can you check if you still see artifacts
> with nosb?

Tried that, doesn't help.

I noticed some things looking questionable in the driver:
- the driver doesn't use the ieee variants consistently (e.g. muls from lerps).
There's also some inconsistencies - for r600, the comments say for non-gl usage
the ieee variant should be used for rcp, however eg/cayman will use that
anyway, and I don't think handling it differently between these drivers is done
on purpose.
- the driver uses min/max instead of min_dx10/max_dx10 (though at least the EG
ISA docs are wrong/inaccurate what they exactly do). These would kill off NaNs
(albeit I am not entirely sure if the non-dx10 version doesn't kill off NaNs
neither, given the docs aren't accurate in the first place...). I think this
probably should be changed (as far as I can tell, radeonsi also uses
effectively the dx10 versions, since llvm.min/maxnum is specified as selecting
non-nan operands, though I don't know if the backend honors it really). This
actually does help things, it removes the black holes in the fires, and the
"vertical blue stripes" (albeit the latter wasn't really in that trace). But
otherwise there's still lots of black boxes around.

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https://bugs.freedesktop.org/show_bug.cgi?id=103544

--- Comment #15 from Roland Scheidegger <sroland@vmware.com> ---
(In reply to Roland Scheidegger from comment #14)
> - the driver doesn't use the ieee variants consistently (e.g. muls from
> lerps).
> There's also some inconsistencies - for r600, the comments say for non-gl
> usage the ieee variant should be used for rcp, however eg/cayman will use
> that anyway, and I don't think handling it differently between these drivers
> is done on purpose.

Actually that seems to be the problem - on r600, rcp/rsq_clamped are used (btw
does someone know why rsq has its own code expansion on r600, but not
eg/cayman)?
But eg/cayman use rcp/rsq_ieee. It looks like if I use rcp_clamped instead that
is enough to fix everything (regardless what rsq/min/max are using).

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https://bugs.freedesktop.org/show_bug.cgi?id=103544

Roland Scheidegger <sroland@vmware.com> changed:

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

--- Comment #16 from Roland Scheidegger <sroland@vmware.com> ---
This should now be fixed by 3835009796166968750ff46cf209f6d4208cda86 (and the
preceding commit).

(Albeit I'm wondering now if I should have used stable tag for these two...).

Closing this, albeit I suppose the simple float blending could still be done.

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