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Why does enabling OpenCL cause my SIM to fail?


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35 minutes ago, marty said:

I got 2x on the pyro and 4x on the smoke solver, adding turbulence nodes to the smoke covered the gap.  This is on Linux, not MacOs where it's not the case.

The overriding issue here is that people read 'OpenCL' and think wham! free speed ups! Sounds like when gamers take the 'must fill up the ram so it can be faster' into the real world -haha

 

Well it is kinda free off the shelf, isnt it? To be fair I havent really used opencl before, but I laid down a box and used the Billowy Smoke shelftool on it, and set the resolution of the sim to 0.01. Running normally the pyrosolver takes 2m15s for 25 frames. Simply enabling the opencl checkbox that time is now 10s for the exact same thing, the sourcing itself actually takes longer now at 12s. The resulting smoke from both sims look pretty much identical. Have I broken something? :D Its a small and short test, but still, didn't expect this dramatic speedup at all.

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@SkybarYay! - that's awesome to hear - kind of makes the bizarre claims 'no speed up claims' even more worrisome doesn't it. I was honestly a bit in shocked that when I jumped from MacOS into Linux OpenCL and it was immediately working, in total contradiction to what is written on the forums. Kind of make me think there isn't any testing before posting.

Spray and pray so the squeaky wheel gets the oil is the motto or maybe the forums aren't for professionals anymore I'm thinking.

Edited by tar
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Simple stuff isn't the problem, it is when you try to really leverage it at the high-end level when it breaks and crashes, does not work and wastes your time.

I was faced with a 170 hour sim time using the CPU. I thought Ok let's leverage OpenCL acceleration, after all I do have compatible card. 40 hours into it, the OpenCL simulation it simply crashes out, with errors similar to the original poster problem. So I lost nearly two days in the process and simply had to revert back to CPU and once again wait out the 170 hours.

The 4GB SideFX limit (perhaps it is an OpenCL limit) I think is the problem, it firmly places you in a fixed resolution. Before I issued the 40 hour OpenCL simulation that failed, I had successfully tested at lower preview quality. This lead me to believe I could leverage the feature. However, once I upped my resolution to production level that is where OpenCL fails on Houdini.

 



 

 

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@Atom  ummm - you're simple throwing large amounts of data that hits a ram limit. Obviously 4GB videocards don't work for large sims, so you then you use CPU OpenCL. Production level work requires thinking about the strengths and weaknesses of the toolset and using it to the most effective level, not whinging ineffectively on the forums. You should be writing .Sim files so when the machine breaks you can pick it up where it stops.   Why do we have to keep writing this? Can you please write it down so you remember and stick it on the wall :lol:

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