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HowardM

Pyro OpenCL vs CPU - Why do the sims differ?

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Can someone please give me an indepth explanation as to why the CPU vs GPU sims look different?

I have noticed when making a fire sim, GPU gives a bit more streaky and jagged sim (better licks) than a CPU sim which tends to be a bit more billowy with more 'shrooms' or rounder shapes in general.

Sadly GPU crashes on any large scale sims yet I really like the look. 

How can I get CPU sims to look as streaky and jagged as GPU?

Any tricks to stop a GPU sim from crashing?

Cheers!

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I noticed the exact same problem. Since my sims usually will cause my GPU to run out of memory I make sure to just to look dev without open cl. For me I think its mainly shredding microsolver that drastically changes look based on open cl on/off. I think maybe I notice it a little on disturbance too.

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Have you reached out to support? This sounds like something they should know about (if they don't already). It affects how the product works in a way that Houdini users wouldn't expect.

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Thats a normal thing. Micorsolvers on openCL calucate things a bit different. I dont think you can expect the sim on CPU and openCL look exactly the same.

 

But I noticed thats not true for all the solvers. Eg. Grain CPU and openCL looks exactly the same.

 

Edited by JJ FX

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You need to set your openCL device to cpu. What I generally do, is test out quickly on the GPU, and when I submit my sim I set the following;

 HOUDINI_OCL_DEVICETYPE=CPU. This will give you the same results. Interesting to note also, that comparing a CPU sim, to a openCL CPU sim can be quite a bit quicker. Have a little search around the docs, to walk you through this.

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11 hours ago, tinyhawkus said:

You need to set your openCL device to cpu. What I generally do, is test out quickly on the GPU, and when I submit my sim I set the following;

 HOUDINI_OCL_DEVICETYPE=CPU. This will give you the same results. Interesting to note also, that comparing a CPU sim, to a openCL CPU sim can be quite a bit quicker. Have a little search around the docs, to walk you through this.

Amazing, cheers!  I will take a look.

 

 

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On 9/5/2018 at 5:53 PM, JJ FX said:

Thats a normal thing. Micorsolvers on openCL calucate things a bit different. I dont think you can expect the sim on CPU and openCL look exactly the same.

 

But I noticed thats not true for all the solvers. Eg. Grain CPU and openCL looks exactly the same.

Cheers, but again I am asking WHY?  What does it compute differently, or what are the main reasons the sims look different?  I would imagine GPU would simply just use the GPU which may sim faster, etc... but why are the maths different, etc...

 

Edited by HowardM

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