[Mesa-dev] [Bug 93686] Performance improvement ?=:=?UTF-8?Q? Please consider hardware ɢᴘᴜ rendering in llvmpipe

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=93686

--- Comment #3 from ytrezq at sdf-eu.org ---
(In reply to Roland Scheidegger from comment #2)
> I'm not sure if this exact same proposal really came up already. We have
> seen some though asking if we couldn't combine llvmpipe with less capable
> gpus to make a driver offering more features, that is executing the stuff
> the gpu can't do with llvmpipe (but no, we really can't in any meaningful
> way).
> This proposal sounds even more ambitious in some ways, I certainly agree we
> can't make it happen. With Vulkan, it may be the developers choice if
> multiple gpus are available which one to use for what, so theoretically
> there might be some way there to make something like that happen, but I've
> no idea there really (plus, unless you're looking at something like at least
> 5 year old low-end gpu vs. 8-core current high-end cpu, there'd still be no
> benefits even if that could be made to work). There is one thing llvmpipe is
> "reasonably good" at compared to gpus, which is shader arithmetic (at least
> for pixel shaders, not running in parallel for vertex ones, with tons of
> gotchas as we don't currently even optimize empty branches away), but
> there's just no way to separate that.

I don’t think it’s necessary to combine 5 years old low end 90nm gpu with a
14nm high end cpu. For example (comparing the hd 2500 integrated graphic of my
ivy bridge cpu and the cpu itself), glxgears (both case in full screen) run at
301 frame per second with the  gpu and 221 frames per second with llvmpipe.
In a gpu intensive OpenGl 3D game (the game itself use 3% cpu), I got 11 frames
per seconds with the gpu and 6 frames with llvmpipe.


I’m also not that sure about high level api : Nvidia is able to perform
complete automatic load balancing with their proprietary drivers (at driver
level) with both OpenGl and Direct3D. It works with all their gpu.

There’s also a well known example of perfect load balancing between several gpu
and several cpu : OpenCl. Though I agree re writing some parts of llvmpipe in
OpenCl might add more overhead than it removes. Plus if it would be possible,
it might remove some of the required manpower to maintain low level hardware
instructions.

Of course in the last two cases, I may be wrong because I might ignore what I’m
really talking about.

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