[gmx-developers] Double precision on GPU's

[James]

Hi Berk,

Thank you for the information. I prefer not to use thermostats, at least
when trying to get quantitative values, because (and I may be
misunderstanding thermostats, but since changing the temperature changes
the energy, I assume this is true) then I cannot use "energy in = energy
out" as a sanity check. I'm more interested in energy balance than in
maintaining a given temperature.

If I were to be able to get the double precision GPU stuff coded, would the
team be willing to maintain it? Or, since I don't know the code, perhaps a
better question is: Does someone who is already familiar with the relevant
code have time to do this as a side project (with compensation)? If anyone
is interested, please feel free to contact me off list.

Thanks,
James

=======================================

Hi,

IIRC all Nvidia Tesla cards have always had double precision, at half
the throughput of single precision. But there are very few cases where
double precision is needed. Energy drift in single precision is never an
issue, unless you really can not use a thermostat.

But having said that, making the GPU code, either CUDA or OpenCL work in
double precision is probably not much effort. But making it work
efficiently requires optimizing several algorithmic parameters and maybe
changing the arrangement of some data in the different GPU memory levels.

Cheers,

Berk

On 7/22/19 10:10 PM, James wrote:
>* Hi,
*>>* My apologies if this question has been previously discussed. I just
*>* joined the list and all I know is that from reading the docs and
*>* release comments, writing code for double precision on GPU's is not a
*>* priority.
*>>* However, I believe all recent upper-end Nvidia cards have native
*>* double precision (which was not true several generations ago). So, you
*>* don't have to have a real "scientific computing" GPU to take advantage
*>* of this -- most people probably already have the hardware. Still, I
*>* understand that most people do not need/want to run double precision.
*>* But, some do (and you have to if you are concerned with conservation
*>* of energy -- the energy drift in single precision is substantial).
*>>* So, I would like to ask what the level of effort to do this is
*>* believed to be? Would it require a lot of new code, or would it be
*>* porting the single precision code to double precision?
*>>* Sincerely,
*>* James
*>
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