ANV Enables UBO Pushing For Another Extra Bit Of Performance

[phoronix]

Phoronix: ANV Enables UBO Pushing For Another Extra Bit Of Performance

With just seven lines of new code, Intel's ANV Vulkan driver is a few percent faster in some Linux games...

http://www.phoronix.com/scan.php?page=news_item&px=Intel-ANV-UBO-Pushing

[davidbepo]

i tested this this in the instancing vulkan demo and it went from 67 to 70 fps
i remember that some time ago that demo ran at 60 fps so nice job with the driver

[CrystalGamma]

Can anyone explain what the difference between push and pull constants is? Is it about how the upload to GPU memory is triggered?

[mczak]

Unless I'm mistaken, with pull constants, if you need access to a constant, you just issue a load instruction in the shader (i.e. you pull the constant to GPR) using a buffer id + offset, which will load it from memory (or caches, hopefully).
With push constants, some fairy instead pushes the constants already to GPRs before the shader is actually executing on the EU.
I don't really know though how exactly this is done (must be done in thread setup or something) or why it's faster. (There are of course obvious limitations, the biggest one that register space is limited so you can't push a lot of constants, large indirectly addressed arrays are right out.)

[CrystalGamma]

That makes sense, thank you very much!