I just made a bug report that included this among a few other issues I found with Karma XPU.

the new change on the usdrenderfile top that requires me to specify the render engines is something I keep forgetting and accidentally have been rendering stuff with Karma CPU. This is something I made a rfe / bug report about a while back.

In this instance though it caused me to discover that render times on karma CPU were pretty similar to karma XPU, which is unfortunate, I'd expect xpu to be a lot faster.

When i rendered some frames on XPU i found that the first frame took longer (i think it had to translate some cop materials or something) and then afterwards it was a little faster.

first frames on XPU:
"BRUH" took 3:27 seconds (64 core threadripper + two a5000s)
"CRUMPUTER" took 2:25 (32 core threadripper + 4090)
"DESKTOP-1HSKGC8" took 3:55 (32 core threadripper + 2 3090s)
"TROGDOR" took 5:16 (12 core intel cpu + 3090)

following frames on XPU:

BRUH 2:59 and 2:48
CRUMPUTER 1:50, 1:50, 1:44, 1:44
DESKTOP-1HSKGC8 3:00, 2:49, 2:44
TROGDOR 4:30

same frames on Karma CPU:

BRUH 2:15, 2:14, 2:14, 2:09, 2:11
CRUMPUTER 2:40, 2:39, 2:47, 2:50, 2:46
DESKTOP-1HSKGC8 3:02, 3:02, 3:10, 3:02
TROGDOR 4:48, 4:58, 5:02

so my machine "BRUH" with a 64 core threadripper and two a5000s was actually significantly faster on Karma CPU than Karma XPU always.

my machine CRUMPUTER with a 32 core threadripper and a 4090 was faster on Karma XPU (no surprise esp with the shader execution reordering stuff that was added)

my machine "DESKTOP-1HSKGC8" with a 32 core threadripper and two 3090s was pretty similar, slower to start on XPU and then slightly faster.

and my machine "TROGDOR" with a 12 core intel cpu and one 3090 was pretty similar too, slower to start on XPU and then slightly faster.

it seems kinda crazy to me that these speeds would be so similar when I have pretty beefy gpus. ill also mention that i'm using
Nvidia Driver 555.99 on BRUH, CRUMPUTER, and TROGDOR.
on DESKTOP-1HSKGC8 i'm using 552.22

on one hand im impressed with how fast karma CPU is rendering the scene, but on the other hand I'm a bit bummed that it's not rendering faster on XPU.
you'd think that having two a5000s would add a lot of extra render speed but apparently it just slows my 64 core cpu down.
karma xpu feels way more optimized for 40 series cards, of which i only have one, and thats the one machine i was getting significant improvements. def makes me wanna sell my 3090s and my a5000s. also kinda makes me want to consider just selling all my gpus and building a cpu farm instead :P

weird, I'm seeing like 5 seconds vs 2 minutes over here. keep in mind the default karma cpu quality setting is like potato mode, sending out maybe 10 samples, default xpu is 128 samples.

Rendered with equal sampling of 128 uniform pathtraced samples on a 10th gen Intel 10 Core with a 3090

Karma CPU 1:45s


Karma XPU 5s


It helps to just not have such a fast CPU

My scene has clouds (volumes), smoke simulation, some instanced bits of particles, a character with SSS, a handful of different objects and shaders and a few lights + per light aovs with LPE tags. So its a bit more complex.


i'm actually not sure what the settings are that its rendering with for cpu, since i have my render settings set to xpu and then the usdrenderfile top is rendering it but changing it to CPU. its set to 256 samples on xpu. idk if its rendering with that many on cpu? regardless though it looks equally clean.

Are you sure the machines are actually using the gpu? We had cases where we rendered with xpu and the Gpu would fail. We also had cases where the cpu and gpu had very weird load. It would go up to 100% load for 2 seconds just to drop to almost nothing for 6 seconds, go back up, etc… i recommend checking the taskmanager (or similar on linux) to see how the load on the cpu/gpu is during those slow xpu renders. To be fair, our problems seems to be related to rendering highres image which xpu which it seems to have problems with (I still need to RFE that)

ronald_a
Are you sure the machines are actually using the gpu? We had cases where we rendered with xpu and the Gpu would fail. We also had cases where the cpu and gpu had very weird load. It would go up to 100% load for 2 seconds just to drop to almost nothing for 6 seconds, go back up, etc… i recommend checking the taskmanager (or similar on linux) to see how the load on the cpu/gpu is during those slow xpu renders. To be fair, our problems seems to be related to rendering highres image which xpu which it seems to have problems with (I still need to RFE that)

Yep I checked and the GPUs seemed to be fully active for the whole time