[Libre-soc-bugs] [Bug 251] Initial 3D MESA non-accelerated software-only driver is needed

[bugzilla-daemon at libre-soc.org]

https://bugs.libre-soc.org/show_bug.cgi?id=251

--- Comment #33 from Jacob Lifshay <programmerjake at gmail.com> ---
(In reply to Luke Kenneth Casson Leighton from comment #32)
> (In reply to vivekvpandya from comment #31)
> > After that we have few options:
> > 
> > LLVMPipe (note official document claims to be multi-threaded and fastest,
> > also that it can generate code for ppc):
> 
> > x86-64, or ppc64le machine code. Also, the driver is multi-threaded to take
> > advantage of multiple CPU cores (up to 8 at this time). 
> 
> hmmm so jacob, where is the limitation that you noted in llvmpipe?

So, for any OpenGL/Vulkan implementation, there are 2 parts (oversimplifying
somewhat) where lots of shader processing happens: the per-vertex/per-triangle
processing and the per-pixel/per-fragment processing. Last I checked, llvmpipe
does parallelize the per-pixel/per-fragment processing but doesn't parallelize
the per-vertex/per-triangle processing. Both are important for performance,
though per-pixel/per-fragment processing is about an order-of-magnitude more
important if just counting the number of times shaders are run, though that can
vary greatly.

A good implementation (such as AMD GPUs, and what is planned for Kazan) will
parallelize both processing stages using both SIMD (or equivalent) and multiple
processors.

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