[Bug 93216] Artifacts with DCC when render target also texture

[Bug 93216] Artifacts with DCC when render target also texture

[bugzilla-daemon]

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https://bugs.freedesktop.org/show_bug.cgi?id=93216

            Bug ID: 93216
           Summary: Artifacts with DCC when render target also texture
           Product: Mesa
           Version: git
          Hardware: Other
                OS: All
            Status: NEW
          Severity: normal
          Priority: medium
         Component: Drivers/Gallium/radeonsi
          Assignee: dri-devel@lists.freedesktop.org
          Reporter: axel.davy@ens.fr
        QA Contact: dri-devel@lists.freedesktop.org

Created attachment 120280
  --> https://bugs.freedesktop.org/attachment.cgi?id=120280&action=edit
Before a buggy draw call

I noticed a few games had some strange artifacts on my tonga that I had not on
verde. Those artifacts are usually along lines.

These artifacts disappear with R600_DEBUG=nodcc.

I managed to determine the bug appears when the render target is also used as
input texture.

Attached is the render target content before and after such draw call. The draw
call draws two triangles. We can see the artifacts are along the border region
of the top right triangle with the bottom left triangle.

My guess is that it is some flush issue. That the bottom left triangle is drawn
first, the cache content of the texture cache updated, and the artifacts are at
locations where the dcc data was updated.

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[Bug 93216] Artifacts with DCC when render target also texture

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https://bugs.freedesktop.org/show_bug.cgi?id=93216

--- Comment #1 from Axel Davy <axel.davy@ens.fr> ---
Created attachment 120281
  --> https://bugs.freedesktop.org/attachment.cgi?id=120281&action=edit
After a buggy draw call

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[Bug 93216] Artifacts with DCC when render target also texture

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https://bugs.freedesktop.org/show_bug.cgi?id=93216

Axel Davy <axel.davy@ens.fr> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
 Attachment #120280|0                           |1
        is obsolete|                            |

--- Comment #2 from Axel Davy <axel.davy@ens.fr> ---
Created attachment 120282
  --> https://bugs.freedesktop.org/attachment.cgi?id=120282&action=edit
Before a buggy draw call

Repost of the first image, reported as PNG instead of text.

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[Bug 93216] Artifacts with DCC when render target also texture

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https://bugs.freedesktop.org/show_bug.cgi?id=93216

--- Comment #3 from Marek Olšák <maraeo@gmail.com> ---
What happens if you set these flush flags after every draw call?

SI_CONTEXT_FLUSH_AND_INV_FRAMEBUFFER
SI_CONTEXT_INV_GLOBAL_L2
SI_CONTEXT_INV_VMEM_L1
SI_CONTEXT_PS_PARTIAL_FLUSH

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[Bug 93216] Artifacts with DCC when render target also texture

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https://bugs.freedesktop.org/show_bug.cgi?id=93216

--- Comment #4 from Axel Davy <axel.davy@ens.fr> ---
I added these at the end of si_emit_draw_packets.

It doesn't solve the problem.

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[Bug 93216] Artifacts with DCC when render target also texture

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https://bugs.freedesktop.org/show_bug.cgi?id=93216

--- Comment #5 from Bas Nieuwenhuizen <bas@basnieuwenhuizen.nl> ---
I think we have cache coherency issues within a single draw call. One of the
situations in which a feedback loop is allowed is if we read and write every
texel at most once and we read the texel from the fragment shader invocation
that writes that texel.

My guess is that this is the case here, with two triangles. The problem is that
while every pixel is written at most once, every block of pixels can be
modified multiple times on the edges of a triangle.

This results in garbage if a later invocation for a tile sees modified pixel
data but stale DCC compression data, or stale pixel data and modified DCC
compression data.


This can be fixed by decompressing the framebuffer and disabling DCC
decompression for the framebuffer. I would like to avoid decompressing, but I
do not know how.

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[Bug 93216] Artifacts with DCC when render target also texture

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https://bugs.freedesktop.org/show_bug.cgi?id=93216

--- Comment #6 from Bas Nieuwenhuizen <bas@basnieuwenhuizen.nl> ---
Does the series available at

https://patchwork.freedesktop.org/series/8048/

fix this issue?

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[Bug 93216] Artifacts with DCC when render target also texture

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https://bugs.freedesktop.org/show_bug.cgi?id=93216

Timothy Arceri <t_arceri@yahoo.com.au> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|NEW                         |NEEDINFO

--- Comment #7 from Timothy Arceri <t_arceri@yahoo.com.au> ---
(In reply to Bas Nieuwenhuizen from comment #6)
> Does the series available at
> 
> https://patchwork.freedesktop.org/series/8048/
> 
> fix this issue?

Hi Axel, those patches landed a long time ago. Is this issue still happening or
can we close this bug?

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[Bug 93216] Artifacts with DCC when render target also texture

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https://bugs.freedesktop.org/show_bug.cgi?id=93216

Axel Davy <davyaxel0@gmail.com> changed:

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

--- Comment #8 from Axel Davy <davyaxel0@gmail.com> ---
The bug seems indeed to have been corrected since.

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