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My daughter has been using blender on a 2015 iMac with 2GB graphics card, 4GHz processor and 32 GB memory. Blender was working great until just now when she applied a smoke effect. She is surprised how much it has slowed. We are wondering if there are any caches or something of that sort that we should be periodically clearing to help speed. The only other app running is a browser where she is watching a tutorial. A few helpers and such are in the background but Activity Monitor shows they are using virtually 0% of CPU, and Blender is only using 2%.

My Question is: Is this normal for the smoke effect?

She is using the number divisions recommended in the "Smoke" tutorial linked below, 256, much higher than the default number of 32. (Alas, I am not up to speed on Blender myself, just repeating what she explained to me.)

https://www.youtube.com/watch?v=snDUjSbBo20&feature=youtu.be

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    $\begingroup$ Maybe its not the CPU, but the RAM thats the bottleneck? (Though 32 GB should be fine) But thats just a shot in the dark... You could try baking down the smoke: docs.blender.org/manual/ja/dev/physics/smoke/baking.html $\endgroup$
    – morph3us
    Commented Oct 13, 2018 at 21:29
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    $\begingroup$ Volumetric data like like smoke simulations are complex and computationally expensive thus requiring lots of processing power, slow downs are frequent and totally expected. Blender doesn't normally use "caches" or leave any sort of garbage littered around your computer that needs regular maintenance. You either need more computing power or to optimize your scene. $\endgroup$
    – Duarte Farrajota Ramos ♦
    Commented Oct 13, 2018 at 23:13
  • $\begingroup$ Thanks, I will show your comments to my daughter :-) $\endgroup$
    – CG43
    Commented Oct 14, 2018 at 3:12

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Yes, this is normal. The fact that the CPU utilization was so low tells me that your daughter has probably 'baked'[1] the simulation to a disk cache so most of the 'work' will be showing up in the form of disk I/O rather than CPU utilization. This is a good thing and probably giving her much better performance than if she 'frees' the bake. The physical sims (smoke, fire, water, soft body) are fun but expensive: they are quite computationally and storage intensive and will often soak up any amount of performance a consumer grade system has to offer. The performance and storage issues get exponentially worse as you dial up the detail, such as going from 32 to 256 divisions.

Some tips to help her deal with this:

  • When you're working out a scene, keep the detail settings of the sim as low as possible to provide the general 'feel' for how it's going to look when it's done. Bake it for performance and work through as much as possible of the rest of the scene.
  • Once you have everything else worked out, free the bake
  • Now then start dialing up the detail level of the sim until it is just above her threshold of 'that looks the way I want it'
  • Bake the sim again at the final detail settings
  • Fine tune / finish up
  • Render the final animation

[1] To determine whether the smoke sim has been baked or not, select the smoke domain and then go to the 'Physics' tab of the Properties browser. At the bottom there is a section 'Smoke Cache' and a set of 6 buttons in a group. If the first button is labeled 'Bake', then she hasn't baked the sim. If it is labeled 'Free Bake', then she has. Either way, the smoke cache defaults to using a sub-directory in the same directory as the main .blend file (so if she has saved it as my.blend, there should also be a blendcache_my-smoke directory)

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