Re: Advice on buying GPUs

From: Axel Kohlmeyer (akohlmey_at_gmail.com)
Date: Mon Jun 06 2011 - 06:50:16 CDT

On Mon, Jun 6, 2011 at 7:39 AM, Ajasja Ljubetič
<ajasja.ljubetic_at_gmail.com> wrote:
> Dear all,
> I'm still in still in the "dream-up" phase of designing my GPU node. Gammer
> mother boards with 3x PCI-E 8x are quite common, but I also found one with

you _have_ to have PCI-e v2.0 16x slots for the GPUs.

> 4x PCI-E 8x. Does it make sense to stuff four GPUs on one node? Can

no. you have only half the bandwidth with a PCI-e 8x slot and will hurt
you more than the 4th GPU will buy you. in my experience, you will
already run into memory bandwidth issues at 3 GPUs. the available
bandwidth is something like sufficient for 2.5 GPUs.
to have 4 GPUs and have them perform well, you need a (server)
mainboard with two southbridges.

> 6 cores feed 4 GPUs? What is the optimum ratio between cores and graphics
> cards? (Or how much over subscription is beneficial?)

if you run on a single node, you will have the largest benefit from
2x oversubscription. everything beyond that is most likely speedup
from the non-GPU part of the namd code.

cheers,
      axel.

> Thank you for your answers & Best regards,
> Ajasja Ljubetič

-- 
Dr. Axel Kohlmeyer
akohlmey_at_gmail.com  http://goo.gl/1wk0
Institute for Computational Molecular Science
Temple University, Philadelphia PA, USA.

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