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CPU usage when GPU rendering

stlkr82stlkr82 Posts: 20
in Daz Studio Discussion
Technical stuff. Week ago I changed hardware in my rig. Ryzen 5 1600X, Asus Prime x370-pro and 2 x 16 gb DDR4 3000 MHz HyperX. Strangely now when I render I have CPU spikes up to 50% when rendering totally on GPU (gtx 1080 8gb). Also Task Manager claims that Daz is using 7 gb of ram when rendering a scene that uses 4 gb of GPU ram.

Comments

  • jurajura Posts: 50
    Hi there This is quite normal with most GPU based renderers, this you can see like with IRAY or SuperFly used in Poser Pro or in Cycles or even in Octane Have look I recently rendered in IRAY 7 G3F, fully clothed and several props and GPU VRAM usage has been in 6.5GB and DS has been using 33.5GB of RAM Yes CPU is used there as well because if you render with GPU or GPUs only, whole scene must fill the VRAM and system RAM as well like SubD, textures and HDR etc and due this don't be scared about that as CPU is always used If you do large renders I always recommend have more RAM, 32GB is probably minimum, 64GB can be more than enough there Hope this helps Thanks, Jura
  • 7thOmen7thOmen Posts: 47

    I am seeing this as well. It started to happen when I upgraded to the latest DAZ Studio.

    The previous version (only a step or two behind - still 4.10.x) would ignore the CPU after all the data was sent to the GPU for rendering. Now, the CPU is averaging 50% usage while on GPU only renders. I can easily confirm that DAZ is the process that is increasing the CPU usage. This has forced me to change my cooling system settings to cope with the added heat the CPU is generating.

    Why is the CPU so active if DAZ has been instructed to only use the GPU? No, there are no other tasks causing this and it happens every time I hit render. I'll also add that the scenes are well within my GPU memory capacity, typically only 50% of vram in use, so nothing is getting dumped off to the CPU due to memory size constraints.

    Ideas?

    Omen

  • prixatprixat Posts: 1,585

    I think that's the render management you're seeing. It has always been handled by the CPU.

    It's where the samples returned from the rendering are evaluated and assembled. It's also where the priorities for the next iteration of samples are decided and sent back to the rendering device.

    It's this part that has changed the most in the last few versions of Iray.
    For example the previous update gave more priority to samples in 'difficult' areas (like shadows) than to easily resolved areas (brightly lit, no shadows). With the idea that you no longer render to 95% in 30s then have to wait an hour for the the last 5%.
    The last update changed the algorithm again this time incorporating the 'Architectural sampler' into the main renderer. It results in a slightly slower render but has eliminated the need switch on a specialised sampler in render settings.

    I haven't noticed the CPU usage spiking to 50% but the log file indicates it always reserves one of the six cores on my CPU for itself.

     

  • 7thOmen7thOmen Posts: 47

    I see.

    Thanks for the explanation.

    Omen

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