[gmx-users] Performance of NVIDIA GTX980 in PCI-e 3.0 x8 or x16 slots ?

[Szilárd Páll]

Good data Mirco, but let me emphasize that your measurements only
reflect the case of heavily GPU-bound workloads!

5-6% performance improvement with PCI-E 3.0 vs 2.0 is about the
maximum you'll see when, like in RF runs where, we there is no enough
CPU work to fully overlap with the GPU computation (indicated  by more
than a few % in the "Waif for GPU" counter). However, if there is PME
CPU work that balance well with the GPU work, while you will still get
shorter CPU-GPU transfer times, the impact of this on the total
runtime will be smaller.

Cheers,
--
Szilárd


On Mon, Jun 15, 2015 at 4:10 PM, Mirco Wahab
<mirco.wahab at chemie.tu-freiberg.de> wrote:
> On 11.06.2015 14:07, David McGiven wrote:
>>
>> Your 1-3% claim is based on the webpage you linked ?
>>
>> Is it reliable to compare GPU performances for gromacs with those of 3D
>> videogames ?
>
>
> OK, you got me on this. As much as I'd wish I cannot
> really back up my claim of comparability. I have been
> out of office for one week but did some tests here
> for myself today.
>
> The system is Haswell/E (i7-5820K), GPU is single GTX-980
> (the "normal" Gigabyte Model), the test run is ADH-cubic-vsites
> (reaction field) from the bottom of the Gromacs acceleration page
> (http://www.gromacs.org/GPU_acceleration).
>
> I can explicitly set the PCIe-x16 slots to 1.0, 2.0, and 3.0
> (which I did). Theoretically (and practically), PCIe-x16 2.0
> should be relatively  close in bandwidth to PCIe-x8 3.0, so this
> should give some hints as what to expect.
>
> adh-cubic-vsites/rf - ns/day:
>   PCIE-x16/1.0  54.46
>   PCIE-x16/2.0  61.81
>   PCIE-x16/3.0  64.52
>
> percentage related to PCIE-x16/3.0
>   PCIE-x16/1.0  84.4
>   PCIE-x16/2.0  95.8
>   PCIE-x16/3.0  100
>
> (each value = avg. of three runs)
>
> Therefore one could support the hypothesis
> that using one card in x16 and one in x8
> would probably show a performance penalty
> of around  5% on the x8 card.
>
> Regards
>
> M.
>
>
> --
> Gromacs Users mailing list
>
> * Please search the archive at
> http://www.gromacs.org/Support/Mailing_Lists/GMX-Users_List before posting!
>
> * Can't post? Read http://www.gromacs.org/Support/Mailing_Lists
>
> * For (un)subscribe requests visit
> https://maillist.sys.kth.se/mailman/listinfo/gromacs.org_gmx-users or send a
> mail to gmx-users-request at gromacs.org.