[gmx-developers] Gromacs with GPU

[Szilárd Páll]

Oh tune_pme is quite unaware about GPU acceleration and I would
actually recommend using it only to tune PME rank count -- which there
is often not much to tune about because the PME load on the CPUs
typically requires around half the cores.

You also have #threads per rank that you'd often want to vary, but
you'd have to do manually.

For the cutoff tuning, I believe the built-in PP-PME balancer is
generally better (AFAIK tune_pme doesn't even use the same  grid size
picking).

--
Szilárd


On Fri, Sep 22, 2017 at 4:02 PM, Åke Sandgren <ake.sandgren at hpc2n.umu.se> wrote:
> Btw, I mostly see this problem when running gmx tune_pme when the npme
> under testing results in there being to few PP processes to utilize all
> GPU engines..
>
> On 09/22/2017 01:54 PM, Åke Sandgren wrote:
>> Ok, then I'll have to write better instructions for our users.
>>
>> On 09/22/2017 01:19 PM, Mark Abraham wrote:
>>> Hi,
>>>
>>> Currently the hwloc support doesn't do much except inspect the hardware
>>> and help produce the report in the log file. Obviously it should be used
>>> for helping with such placement tasks, and that's why we're adopting it,
>>> but nobody has prioritized specializing the task-assignment code yet.
>>> For the moment, such things are still up to the user.
>>>
>>> Mark
>>>
>>> On Fri, Sep 22, 2017 at 1:10 PM Åke Sandgren <ake.sandgren at hpc2n.umu.se
>>> <mailto:ake.sandgren at hpc2n.umu.se>> wrote:
>>>
>>>     Hi!
>>>
>>>     I am seeing a possible performance enhancement (possibly) when running
>>>     gromacs on nodes with multiple gpu cards.
>>>     (And yes I know this is perhaps a mote point since current GPU cards
>>>     don't have dual engines per card)
>>>
>>>     System:
>>>     dual socket 14-core broadwell cpus
>>>     2 K80 cards, one on each socket.
>>>
>>>     Gromacs built with hwloc support.
>>>
>>>     When running a dual node (56 core)
>>>
>>>     gmx_mpi mdrun -npme 4 -s ion_channel_bench00.tpr -resetstep 20000 -o
>>>     bench.trr -x bench.xtc -cpo bench.cpt -c bench.gro -e bench.edr -g
>>>     bench.log -ntomp 7 -pin on -dlb yes
>>>
>>>     job, (slurm + cgroups), gromacs doesn't fully take hwloc info into
>>>     account. The job correctly gets allocated on cores, but looking at
>>>     nvidia-smi and hwloc-ps i can see that the PP processes are using a
>>>     suboptimal selection of GPU engines.
>>>
>>>     The PP processes are placed one on each CPU socket (according to which
>>>     process-ids are using the GPUs and the position of those pids according
>>>     to hwloc-ps), but they both uses gpu engines from the same (first)
>>>     K80 card.
>>>
>>>     It would be better to have looked at the hwloc info and selected CUDA
>>>     devices 0,2 (or 1,3) instead of 0,1.
>>>
>>>
>>>     Any comments on that?
>>>
>>>     Attached nvidia-smi + hwloc-ps output
>>>
>>>     --
>>>     Ake Sandgren, HPC2N, Umea University, S-90187 Umea, Sweden
>>>     Internet: ake at hpc2n.umu.se <mailto:ake at hpc2n.umu.se>   Phone: +46 90
>>>     7866134 <tel:090-786%2061%2034> Fax: +46 90-580 14 <tel:090-580%2014>
>>>     Mobile: +46 70 7716134 <tel:070-771%2061%2034> WWW:
>>>     http://www.hpc2n.umu.se
>>>     --
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>>>
>>>
>>
>
> --
> Ake Sandgren, HPC2N, Umea University, S-90187 Umea, Sweden
> Internet: ake at hpc2n.umu.se   Phone: +46 90 7866134 Fax: +46 90-580 14
> Mobile: +46 70 7716134 WWW: http://www.hpc2n.umu.se
> --
> Gromacs Developers mailing list
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