From: Francesco Pietra (chiendarret_at_gmail.com)
Date: Mon May 28 2012 - 14:46:54 CDT
Thanks for your lucid illustration. It will be useful at large.
There is at least another consumer motherboard, claimed for multi
GPUs. I'll check whether a meaningful description is provided.
On Mon, May 28, 2012 at 6:20 PM, Axel Kohlmeyer <akohlmey_at_gmail.com> wrote:
> On Mon, May 28, 2012 at 12:03 PM, Francesco Pietra
> <chiendarret_at_gmail.com> wrote:
>>> When referring to NAMD, I wanted to imply (badly, I admit) performance
>>> boost by the third GPU.
> as i was mentioning before. that is near impossible to predict.
>>> The 990FXA-GD80 PCI specification is described by the manufacturer as follows
>>> -- PCI Express slots version: 2.0.
>>> -- PCI slots: 1.
>>> -- PCI express x1 slots: 1.
>>> -- PCI express x16 slots: 4.
> that doesn't mean anything. labeling slots as x16
> only means that you can stick an x16 wide card
> into it. each of these slots can be wired with 16,
> 8, 4, 2 or 1 lane. also, some boards claim they
> have all 16-lane slots, but then two slots are
> connected to a little bridge chip. resulting in
> two cards each having to share the bandwidth.
>>> Whether these are real x16 2.x, or not, is beyond my understanding. I
> with out that information, you can't judge.
> contact the vendor or find somebody that
> has time to research it.
>>> can only compare with the corresponding description for the mainboard
>>> I am currently using: GA-890FXA-UD5:
>>> 2 x PCI Express x16, running at x16 (PCIEX16_1, PCIEX16_2).
>>> 1 x PCI Express x16 slot, running at x8 (PCIEX8).
>>> 1 x PCI Express x16 slot, running at x4 (PCIEX4).
>>> 2 x PCI Express x1 slots.
>>> (All PCI Express slots conform to the PCI Express 2.0)
>>> 1 x PCI slot.
>>> With this latter mainboard, adding a second GTX-580 gave the expected
>>> acceleration. Data for PCIs of the two mainboards being comparable, I
>>> would expect that a third GTX-580 on the 990.. motherboard should play
>>> well its job. Is it this naive extrapolaion a sound one?
> no. you usually overload the memory bandwidth of the CPU
> with the third GPU and thus you won't get the full speedup.
> how much speedup you'll get depends on the individual
> characteristics of your input.
>>> Thanks indeed for further advice
>>> francesco pietra
> Dr. Axel Kohlmeyer
> akohlmey_at_gmail.com http://goo.gl/1wk0
> College of Science and Technology
> Temple University, Philadelphia PA, USA.
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