[gmx-developers] 4.6 Binaries and Acceleration levels

[Szilárd Páll]

On Thu, Jul 5, 2012 at 10:59 PM, Christoph Junghans <junghans at votca.org> wrote:
> 2012/7/5 Szilárd Páll <szilard.pall at cbr.su.se>:
>> On Thu, Jul 5, 2012 at 8:11 PM, Roland Schulz <roland at utk.edu> wrote:
>>> Hi,
>>>
>>> with the new large number of GMX_ACCELERATION options (SSE2, SSE4.1,
>>> AVX_128_FMA, AVX_256) for X86 it's going to be very difficult to make
>>> efficient binary packages. This effects both us if we provide binaries
>>> and the Linux distributions. Either one only has SSE2 binaries or one
>>> has to create a large number of binaries and let the user choose the
>>> correct one. In the first case the user might get significant lower
>>> performance then would be possible.
>>>
>>> Has the option to allow setting GMX_ACCELERATION to more than one
>>> value been discussed?  Wouldn't it be relatively easy to compile the
>>> same kernel more than once with different defines and use a macro to
>>> add the acceleration in the function name of the kernel (E.g.
>>> nbnxn_kernel_x86_sse41_simd128)? That way one could create one binary
>>> which has all accelerations and the correct one would be chosen at
>>> runtime.
>>>
>>> Otherwise I expect that everyone using mdrun from a binary Linux
>>> distribution is getting only SSE2 acceleration. Obviously I'm very
>>> late with suggesting that but the new GMX_ACCELERATION options have
>>> also only just been added given little time to think about how to make
>>> binary distributions.
>>
>> Indeed, that's a *major* drawback and we haven't thought of it at all.
>> Additionally, all these users will be annoyed by the run-time
>> detection which will keep on telling them that mdrun is not using the
>> optimal level of acceleration.
> Roland has a good point, but Debian and Fedora already compile Gromacs
> for different mpi version.
>
> 4 acc. x 3 (serial,openmpi & mpich2) = 12 packages!
>
> @ Jussi: Would that still be possible?

I guess possible is one thing and probable is a totally different one...

Perhaps it would be good to ask the Ubuntu/Debian maintainer as well...

--
Szilárd

>
> Cheers,
>
> Christoph
>
>
>>
>> --
>> Szilárd
>>
>>> Roland
>>>
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>
>
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> Christoph Junghans
> Web: http://www.compphys.de
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