[Mesa-dev] [PATCH 00/11] i965: UBO pushing for fun and profit?

[Matt Turner]

On Thu, Jul 6, 2017 at 5:22 PM, Kenneth Graunke <kenneth at whitecape.org> wrote:
> Hello,
>
> This series begins pushing UBOs (rather than resorting to pull loads)
> for scalar shaders on Gen7.5+, for the OpenGL driver.  Future work is
> to hook it up for Vulkan (haven't started), for the vec4 shader stages
> (I have about 75% of the code written), and for Gen7 (I have a plan).
>
> Note that compute shaders unfortunately still resort to pull messages,
> because I haven't found a way to make the constant commands absolute
> addresses instead of being relative to dynamic state base address.
>
> This has long been a gap in our UBO support - we pushed regular
> uniform data, but always resorted to pulls for UBOs, making them
> slower than regular uniforms.
>
> I started this project a year and a half ago, and it initially looked
> very promising - up to 30% faster in Tomb Raider, for example.  However,
> Curro improved the performance of pull messages significantly since then.
> Now, it doesn't seem to have as large of an impact.  Jason thinks this
> would help close the GL/Vulkan gap in Talos Principle, when we finally
> hook it up in Vulkan.  One place where it does help is GLBenchmark 3.1
> Manhattan, which improves 3-4% on most platforms, and 6-7% on SKL GT4.
> This is primarily because it avoids doing a pull load in a loop, though,
> which could be solved by using the global code motion pass...
>
> I figured I'd at least send it out for an initial review, and we can
> continue collecting benchmark data...

The series looks good to me. I'm not the ideal person to review state
upload changes, so take that review for what its worth.

Reviewed-by: Matt Turner <mattst88 at gmail.com>

I guess we just need benchmarking data. Also, a set of todos I noticed

- give higher weight to UBO accesses in loops (and less if in an if?)
- consider combining ranges, but ugh, heuristics

I'm definitely okay with leaving those until a time when we find they're useful.