[Sidefx-houdini-list] open cl and quadro on h12

John Lynch johnerlists at austin.rr.com
Thu Aug 16 18:43:48 EDT 2012

On 08/16/2012 04:44 PM, crydalch at sidefx.com wrote:
> On whether the GPU and CPU versions produce the same results, they 
> should as both are using OpenCL. From the Pyro 2 description:
> /
> "The hardware acceleration uses OpenCL, which is compatible with the 
> OpenCL library on the CPU. This means that a simulation prototype 
> performed using the GPU one the workstation _will produce identical 
> results _if run non-interactively on a headless farm."/

Hmm, well that's only true if the CPU simulation is actually using the 
OpenCL CPU driver, rather than just turning off the "Use OpenCL" option, 
which will take a completely different, non-OpenCL code path.  From my 
experience the OpenCL / non-OpenCL sims are fairly close in appearance, 

Even if you are using an OpenCL CPU driver on the farm, you still might 
get slightly different results due to different ordering of floating 
point instructions.  So for example, if you prototype on a workstation 
with an NVIDIA GPU, then run the same simulation on the AMD CPU driver 
on the farm, you'll be using the same code but compiled with two 
different compilers, essentially.  So the results should be very 
similar, but probably not exactly identical due to possibly different 
instruction ordering (which is probably what the documentation should 
say, FWIW).

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