Slow Phoenix 3 rendering ?

[anthonyh]

Hi,
I`m using Phx 3.14 latest nightly 30113 and vray 3.7 latest and rendering an animation with backburner I`m noticing heavy slowdowns with rendering and possibly simulating too.
We have 1 Threadripper 1950X and 3 TR 2990WX. Usually the TR 2990s are at least twice the speed with rendering but on a purely Phoenix scene (no geometry only Volumetric sim) they are using around only 50-60% of the processor and rendering 1/3 to 1/2 the speed of the TR 1950 ? I don`t really know why.

I don`t think it`s overheating as normal Vray scenes(geometry+ GI etc) render and max the cpu at 100% and they are fine.
I also rendered an ocean scene a few days ago before upgrading to the latest nightly and they seemed to render at the proper speed although I`d have to send again to check.
I`m not using any GI or Light cache as it`s just a simple modified Cigarette Smoke preset, Phx particles. I`ve tried previous Phoenix nightly versions and they all render slower like this so I guess it must be the smoke scene ? What is it about Cigarette smoke that renders 2-3 times as fast on a TR1 vs TR2 ?
From the task manager it seems like the TR2s are only using half the cores at 100% and the rest are lazy around 10-50% some of the time. But if I send a geometry render to backburner it uses 100% again. Can`t figure it out. Pretty sure I`ve reinstalled to make sure everything is on the same version but I`d expect some disparity between the 3 TR2s. Unless Phx uses GPU for anything as these are render slaves so only have a very basic Geforce GPU vs the TR1 which has higher GPU but then wouldn`t that also affect geometry renders ?

One side question, is there really no expected speed gain when simulating between my old Core i7 3930k and TR2 299WX ? I know they`re not directly comparable but my Core i7 is using 50% cpu when simming whereas the 2990WX uses 6-10%. Is that expected or is this something likely wrong as per above ?
thanks

[georgi.zhekov]

Hey,

Does the slowdown happens only with the cigarette smoke preset? What if you try to render the large scale smoke preset in a new scene? Can you send us the problematic scene so we can check it out?
Just a shot in the dark, but for the cigarette smoke scene - does it get better if you disable the Volume light cache checkbox in the Particle shader options?

As for the simulation part.

You can check our hardware recommendations here - https://docs.chaosgroup.com/display/...sterSimulating

Phoenix will use all of the cores that are available. Though, it's really important to note that processor speed is more important than core count. Also, NUMA (such as the Threadripper) and multiprocessor architectures do not perform well with Phoenix. Simulating on one NUMA node is often faster than waiting for multiple nodes to synchronize.

The CPU utilization really comes down to the type of simulation you're running. If the sim is relatively low res and a frame is simulated quite fast - in the Task manager it might show something like 20% CPU, because it barely starts and it has to stop to write down the cache to disk.
If the simulation takes a bit more time per frame you will notice that the CPU gets 100% utilization.

Cheers,

[anthonyh]

Hi Georgi,

>does it get better if you disable the Volume light cache checkbox in the Particle shader options?
..testing it now..Yes that`s it, looks like you hit the answer right away, Thanks ! It`s back to 100% cpu and render times back on par. To be honest I`d have thought thought this would be ignored(same as tick off) if GI/Light Cache was switched off in Vray Settings as mine is.
Now I just have to remember to switch if off in future !

I also tried a Large Smoke sim and it`s fine, I assume because it doesn`t have an associated Phoenix Shader so the Volume Light Cache isn`t an option.

As for sim speed, we were looking with new pcs in mind to help speed Phoenix up but it has to be a Workstation first and foremost and given current cpu development is pushing multicpu above speed it doesn`t seem like Phoenix is going to gain any real significant benefit without some very specific hardware we likely can`t afford.

thanks Georgi