[gmx-users] Cuda CC 2.0 restrictions

[Szilárd Páll]

Hi,

Is this rather large box a system that can actually be simulated with
a useful speed on a single Fermi GPU? Even with 5 fs time-step you
won't get much more than 1-1.5 ns/day on a fast Fermi GPU like a GTX
580.

Given that you are quite a bit above the limit, unless you are using a
quite large nstlist, you may not be able to decrease it enough to fit
the system on the GPU. What you can do instead is to use
domain-decomposition and start multiple ranks per GPU. In your case
two-way DD should be enough.

Cheers,
--
Szilárd


On Fri, Sep 5, 2014 at 11:24 PM, Mirco Wahab
<mirco.wahab at chemie.tu-freiberg.de> wrote:
> I've run into a problem with an older card (GTX-580)
> which is CC 2.0. On a larger box size, mdrun stops
> with:
>
>    Fatal error:
>    Watch out, the input system is too large to simulate!
>    The number of nonbonded work units (=number of super-clusters)
>    exceeds themaximum grid size in x dimension (86276 > 65535)!
>
>
> This seems to refer to the CUDA "grid of thread blocks per dimension",
> limitation specific for CC below 3.0 (I know this system worked already
> on a CC 3.0 device).
>
> My question: can this grid count calculated by mdrun be "manipulated"
> somehow by mdp options (nstlist, rvdw, rlist)?
>
> Thanks,
>
> M.
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