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Iray is not using CPU?

alexmairalexmair Posts: 0
in New Users

I just made a test rendering the same image with cpu and gpu and only gpu. With GPU it took 48 seconds and with CPU and GPU it took like 1 min and 3 seconds. 

How is that possible, or am I doing anything wrong?

I have a Ryzen 1800x, 32 GB of RAM and a 1080 from asus

Comments

  • agamersdayagamersday Posts: 101
    This is normal. You'd expect that the cpu is helping but I find it actually slows it down a bit. You especially notice that when going into iray preview mode, with gpu only it loads up way quicker so I usually leave cpu off.
  • bitwelderbitwelder Posts: 212

    Yup, me too--I get faster results by leaving the CPU out of it altogether.

  • ToborTobor Posts: 2,300

    As an FIY, be sure to always time things from the same starting point. Don't go by the render info window (or troubleshooting log) alone. If you have a stopwatch function on your phone, start timing at the first iteration, and go until it reaches 100%. There are other timings involved that can confuse how long the actual render took place.

    That said, the CPU is involved in aspects of the render (scene set up, code cleanup, etc) that the GPU is not. So if it's not also used for rendering, it's more free to perform those duties. You might find, for example, that it takes much longer to cancel a render if you have the CPU on.

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