Re: [AMBER] GTX680

From: Fenley, Andrew <>
Date: Thu, 29 Mar 2012 02:33:53 +0000

Hi Scott,

Curiously, is the hopeful 85-95% performance of a GTX 580 for pmemd SPDP? And if so, and assuming the GTX 680s don't have similar "breaking" issues when running in parallel, is there any expectation that the pci-express 3.0 architecture and cuda 4.x would result in two GTX 680s out performing two GTX 580s (or rather two M2090s) when running parallel?


On Mar 28, 2012, at 9:33 AM, Scott Le Grand wrote:

The upshot is that I expect it to only deliver 85-90% of a GTX 580. And
that's partially because there's no increase in memory bandwidth and mostly
because of the regression in double-precision performance. And that's a
shame because single-precision *screams* on this chip.


On Fri, Mar 23, 2012 at 11:57 AM, Scott Le Grand <<>>wrote:

I am very optimistic about GTC680 performance...

That said, anyone who hacks the configure script to make the current code
run will be severely (an unnecessarily) disappointed. Every AMBER kernel
has been meticulously shoehorned into GTX2xx and GTX5xx GPUs. GTX680 is a
radical redesign of Fermi (please don't listen to the dunderheads on review
sites blathering about matters that's beyond them about such things,
seriously). That radical redesign has created a much more efficient GPU
(I'm expecting the perf/watt on AMBER to hit transwarp as opposed to merely
warp drive in the near future) but it's been at the expense of 33% higher
operational latency.

33% higher operational latency is fine - except that the shared memory on
GTX680 is exactly the same as GTX580 and that's leading to a ~30%
performance deficit if one just runs the existing code. However, there are
2x as many machine registers on GTX680 than on GTX580. Or TLDR: I need to
rewrite every single kernel for GTX680 from the ground-up to hit attainable

So give me a few weeks, mmkay?


On Fri, Mar 23, 2012 at 11:49 AM, Ross Walker <<>>wrote:

Hi Filip,

Hi all,
I was wondering
what we can expect from GTX680 and in general from the new Kepler line.
I know
that GTX680 is very limited DP, but should be good in SP mode. Would we
some speed boost compared to GTX580 and also will it work along Amber

Amber 11 will NOT support the GTX680 cards (unless you hack the configure
script to compile it in what is effectively an emulation mode). It will be
too much work to make patch against that. AMBER 12 will support them but it
is going to take around 6 weeks to 2 months to get the optimization done
and a patch released so it won't support the cards at release but it will
as soon as we have the patch ready. I can't really give you any performance
expectations right now, only got my first prototype board yesterday. ;-)

Right now if you compile AMBER 12 with PTX support so that it will at
least run on the GTX680 the performance sucks. It is about 70% of a GTX580.
NVIDIA changed the hardware too much (massively increasing the threads but
also the thread latency) so it will need some work to optimize it which is
why I have chosen not to support the cards in AMBER 12 until we have that
optimization done. Once it is done I expect considerable improvement over
GTX580 speeds but can't give you anything concrete right now.

P.S. Indeed most
of us will probably wait for GK110, but CUDA capability of GTX680 is
very limited now.

This is probably a good idea, at least you should wait until we have had
a chance to get our hands dirty with the GK104 chip. So I'd urge you to
wait at least until we have the patch ready for AMBER 12.

All the best

|\oss Walker

| Assistant Research Professor |
| San Diego Supercomputer Center |
| Adjunct Assistant Professor |
| Dept. of Chemistry and Biochemistry |
| University of California San Diego |
| NVIDIA Fellow |
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| Tel: +1 858 822 0854 | EMail:-<> |

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Received on Wed Mar 28 2012 - 20:00:03 PDT
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