Re: Is GPU double-precision floating point performance important for NAMD?

From: Mert Gür (gurmert_at_gmail.com)
Date: Fri Jun 03 2016 - 09:20:42 CDT

That, actually clears up a lot of things.

Thanks a lot.

Mert

On Thu, Jun 2, 2016 at 11:49 PM, Norman Geist <
norman.geist_at_uni-greifswald.de> wrote:

> Hi,
>
>
>
> as far as I know, NAMD doesn’t use any double precision numbers on the
> GPU, so your assumptions are right so far.
>
>
>
> The use of Tesla cards is meant for professional clusters, not for
> individual workstations. Their advantages for big cluster systems are:
>
> 1. Longer product cycle
>
> 2. Built for 24/7 use
>
> 3. Some exclusive features like GPU-Direct
>
> 4. ECC Support (Easier to find a broken GPU out of many)
>
> Disadvantages are:
>
> 1. Expensive
>
> 2. Lower clock for the sake of stability and reliability
>
> 3. Slower due ECC for the sake of stability and reliability
>
>
>
> So it’s common knowlegde that GeForce are faster, as they have higher
> clocks and lack ecc., but therefore they are likely to die earlier, which
> is not important if you have just one of them, since you could buy any
> newer card then, but it would be if you would have 100s of them in a
> cluster, where you would have to find the broken one 1st, and would want
> to replace it with the same modell again.
>
>
>
> Hope that clears up some things ;)
>
>
>
> Norman Geist
>
>
>
> *Von:* owner-namd-l_at_ks.uiuc.edu [mailto:owner-namd-l_at_ks.uiuc.edu] *Im
> Auftrag von *Mert Gür
> *Gesendet:* Donnerstag, 2. Juni 2016 23:48
> *An:* NAMD list <namd-l_at_ks.uiuc.edu>
> *Betreff:* namd-l: Is GPU double-precision floating point performance
> important for NAMD?
>
>
>
> Dear all,
>
>
>
> When I am running GPU accelerated MD simulations in NAMD, are there any
> double precision floating number calculations performed on the GPU? In
> other words how much should I care about the double precision performance
> on the GPU if I am running NAMD?
>
>
>
> Is there any source/documents that explains this extensively?
>
>
>
> What is the double-precision point performance I am looking for in a GPU.
>
>
>
>
>
> For example the K80 has
>
> Peak double-precision floating point performance: 1.87 Tflops
>
> Peak single-precision floating point performance 5.6 Tflops
>
> CUDA cores 4,992
>
> Memory size per board (GDDR5) 24 GB
>
>
>
> whereas the Titan x has (if I am not mistaken)
>
>
>
> Peak double-precision floating point performance: 200 GGflops
>
> Peak single-precision floating point performance 7 Tflops
>
> CUDA cores 4,992
>
>
>
> The new GTX1080 is said to give 10.7 TFLOPs of single precision
> performance.
>
>
>
> So if GPU doube-precision performance is not that important for NAMD;
>
>
>
> Obviously GTX 1090 and Titan X would give me better single precision
> performance than K80. Doesn't that mean I would get faster MD simualtions
> on GTX1080 compared to the others?
>
>
>
> If that is the case why should I select a K80?
>
>
>
>
>
> Does double-precision performance of the GPU matter if I apply any type of
> bias or perform accelerated MD?
>
>
>
> My understanding (from past emails on the list) is that the "ECC error
> correction" GPU feature is also not (that) important for NAMD. Can someone
> ellaborate on this or point me to a link/document which I can read.
>
>
>
>
>
> Thanks,
>
>
>
> Mert
>

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