36 thread limit?

[pikalabs]

Hi,

Wondering if rendering is limited to 36 threads or whether I'm missing something here. See attached.

This is Amazon EC2 c5.18xlarge. I want to do some render time comparisons on various EC2 configurations .

thanks!
brook

[Fletch]

We have never tested on this type of configuration.
It is possible there is some sort of 36 thread limit. But if there is we are not aware of it, you are the first person to mention this issue.

If I had 72 threads I would be rendering with Easy09, not Easy07, as the quality will be better and render times maybe faster in the scene shown in the screen shot.

[pikalabs]

That makes sense, ya. I plan on using Easy09 on this system for production rendering.

I actually can increase the threads to 72 manually, just noticed that. However on the lamp speed test model this increases rendering times considerably.

The system is (reported to be) dual CPU, each 18 core / 36 thread for a total of 36 core / 72 treads. In the case of hyperthreading like this, maybe using all 72 treads isn't ideal anyway?

[Chris]

I believe you are correct. When running a CPU core at 100%, hyper threading is not effective. And if there is only one floating point processor per core, all the more reason to just run 1 thread per core for rendering.

[pikalabs]

Got it, thanks! Will continue some testing.

I believe you are correct. When running a CPU core at 100%, hyper threading is not effective. And if there is only one floating point processor per core, all the more reason to just run 1 thread per core for rendering.