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What's Going on with my Render Times?

sandmanmaxsandmanmax Posts: 992
edited April 2022 in The Commons

I've got a scene with one G8F and one G81F (with clothes and hair), HDRI being used for the background.  When I render the whole scene, it takes 1 min 21 sec on my Titan X 12gb graphics card.  Using a different camera, I rendered a close-up of G81F and it went to CPU and took almost 12 minutes.  It's the exact same scene, nothing changed.  I tried closing DS and reloading the scene, rendered the close-up again.  Still CPU, still 12 min.

According to the log file, the memory consumption is:

2022-04-10 14:33:13.888 Iray [VERBOSE] - IRAY:RENDER ::   1.5   IRAY   rend stat : Texture memory consumption: 1.676 GiB for 103 bitmaps (device 0)
2022-04-10 14:33:13.889 Iray [VERBOSE] - IRAY:RENDER ::   1.5   IRAY   rend stat : Lights memory consumption: 431.410 KiB (device 0)
2022-04-10 14:33:13.889 Iray [VERBOSE] - IRAY:RENDER ::   1.5   IRAY   rend stat : Material measurement memory consumption: 0.000 B (GPU)
2022-04-10 14:33:13.890 Iray [VERBOSE] - IRAY:RENDER ::   1.5   IRAY   rend stat : Materials memory consumption: 378.305 KiB (GPU)

I check after both renders and these number are the same for both.  Does anybody have any ideas why the close-up would go to CPU? (I used DS 4.16.03 for these tests.)

 

Post edited by sandmanmax on

Comments

  • SevrinSevrin Posts: 6,309

    Do you have windows open from previous renders when this happens?  Since Iray isn't done with those until you save the images or just close the windows, they still take up VRAM.

  • sandmanmaxsandmanmax Posts: 992
    edited April 2022

    That's certainly a consideration, because I do leave them open all the time. But that wouldn't have been the case when I closed and re-opened DS.

    I repeated the tests in DS 4.20.0.11 and got similar results.  Here are the images.  Is DS doing some kind of internal optimazation or something?  I can understand why the close-up might take longer, due to all the reflective surfaces (eyes, mouth, teeth) and transparency of the hair, which would be minimized in the full-body render.

     

    All GPU Render.png
    790 x 1279 - 2M
    CPU Render.png
    790 x 1279 - 2M
    Post edited by sandmanmax on
  • rrwardrrward Posts: 556

    Looking at your images, I'm not surprised at all. Hair is very expensive to render. 

  • ioonrxoonioonrxoon Posts: 894

    It's not unusual, the closer you get with the camera to your characters, the longer the render will take. There's a lot more detail in a close-up, than with the characters far away.

  • Matt_CastleMatt_Castle Posts: 2,652

    An HDRI backdrop is extremely quick to render, and the figure is where the work is here (particularly skin and hair), so the figure filling more of the frame will take longer.

    Were this a scene with a modelled background, particularly an interior background that needs lots of light bounces, you'd see a lot less difference in the render times between close-up and distant, because the background would be more work to render in the first place.

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