Arnold using AVX instruction / CPU clock speed dips during render

[cgpyos]

MtoA 3.0.0.2

I've set my AVX (non-512) negative offset to maintain reasonable temperatures, bc this CPU get really power hungry (hot) when using it. I've mentioned that during render my CPU downclocks to AVX frequencies which are 3.9 ghz.

The question is, in which version of MtoA AVX instructions usage was introduced, and what's are cases when Arnold uses it?

[maxtarpini]

mmhm.. it’s very difficult to say that CPU throttling (what you call downclocking) is a deterministic frequency reduction based on some instructions usage .. in facts most of the time, - throttling happens anyway when the CPU uses a lot of power and becomes too hot.

take care compilers can use AVX instructions even if you ain’t using’em explicitly like for coping struct, inlining memcpy or vectorizing loops etc. however the SIMD speed up generally voids the frequency slow down, so even if you see lower numbers your computation performance should be higher.

eventually be sure your system is super stable and super well-cooled then try using only 1 or 2 cores and see if your CPU keeps stepping down into a well defined license mode (lookup L0, L1, L2 nominal frequencies for your CPU). Only with sustained dense heavy use (1 x cycle) of AVX instructions you go to L2, with light use you may go to L1. if your frequency drop is arbitrary (well.. sort of) then it’s not that, however it could still be not that even if your discrete stepping down uses known patterns.

this said .. I really don’t think you should be worried about anything your CPU is doing regard its core frequencies 🙂

[Stephen.Blair]

Arnold doesn't have any AVX-specific code.

[Slava_91]

Yes, I have same deal
Arnold working on frequency for AVX instruction
if I reducing AVX offset values, arnold will adjust to it

[thiago.ize]

There is no AVX code in Arnold (it will run on a pre-AVX CPU). However, Arnold makes use of system libraries, for instance for copying data, and these libraries could be using AVX.

[maxtarpini]

Slava can you run Linux or at least WSL on Windows 10 ?

The attached linux apz is a mini-renderer that does some SSS computation with and without AVX-2. On WSL first 'cd' to Desktop (where you unzipped the app).. $ cd mnt/c/Users/USERNAME/Desktop Then run it as you'd do in Linux: $ ./app_dirpole 50000

50000 samples should be plenty enough to let you inspect your CPU in the while 🙂

The first part is parallel rendering with OPENMP. The second is both parallel across SIMD lanes (using AVX) and across multiple cores. See last paragraph in the other post I did here to see if your CPU is throttling because of AVX or simply because is getting freaking hot (or uber busy and you have some BIOS setup..).

https://www.rombo.tools/downloads/app_dirpole.zip

Eventually, here if you plan to compile it yourself:

https://github.com/RomboDev/Miscellaneous/tree/master/ISPC%20Directional%20Dipole