[gmx-developers] 4.6 Binaries and Acceleration levels

[Szilárd Páll]

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.

--
Szilárd

> Roland
>
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