[Bug 110228] [cfl] GPU hang when running UE4Editor

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=110228

--- Comment #30 from Jason Ekstrand <jason at jlekstrand.net> ---
Put a bit more time into it.  Here's what I have so far:

 1. Inserting a barrier() does nothing

 2. Setting MOCS = 0 on the buffer used for the atomic makes than hang go away.

 3. If I hack up the driver to use an untyped atomic instead of a typed atomic,
no change.  It still hangs so typed vs. untyped doesn't seem to matter.

 4. If I hack the driver up to use SUFTYPE_1D instead of SURFTYPE_BUFFER for
the uniform texel buffer, the hang goes away.

 5. If I use SURFTYPE_1D for the VkBufferView with the atomic and
SURFTYPE_BUFFER for the uniform texel buffer, it hangs.

It's very much starting to look like it's just a weird interaction between
atomics, the L3$, and the sampler with SURFTYPE_BUFFER.  Unfortunately, that
means our options for mitigating it are somewhat limited.  We can't just use
SURFTYPE_1D for all buffer textures because that has a limited width of 16K and
I really don't want to start disabling L3 caching on all atomics.

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