Hi Filip,
>As you know I plan to purchase few GTX Titans:)
>but I am not sure actually at what speed they will run: 836, 876 or 993
>Mhz?
>It seems that by default (80C target) the Titan
>runs under Windows only on the maximal core speed (around 1Ghz) not the
>boost
>one. It goes back to 836 only if the temperature rises above 80C but with
>100%
>fan speed this looks almost impossible. At least this is what I saw from
>the
>reviews.
No idea since I am still waiting for NVIDIA to actually send me a
development card to try this with. I guess the Titan's will be vaporware
for a while. I am intrigued to know about how the clock speed will work
and I am waiting for NVIDIA engineering to get back to me with a
definitive answer. Note the Titan can also be run in two modes from what I
gather. One with the DP cores turned down and the SP cores clocked up
(Gaming mode) and one where it turns on all the DP cores and clocks down
the single precision (CUDA mode). Note AMBER was retooled for the GK104
chip to not use double precision anymore. It uses a combination of single
and fixed precision which we worked very hard to tune to match/better the
SPDP accuracy. Thus it is entirely possible that one will actually want to
run the Titan cards in gaming mode when running AMBER. Of course this is
entirely speculation until I lay my hands on one. The thermal window also
has potential issues for 4 GPU boxes but there may end up being a hack to
disable the down clocking and allow temps over 80C. Note most cards I have
(GTX680s) run around 90C right now. SDSC runs it's machine room at 85F in
order to save power - since disks and CPUs don't care if the room is 85F
vs 60F. This might be a different story if the GPUs throttle based on
temperature but I guess we'll just have to wait and see.
>
>I was also horrified to see that many GTX680
>(and other cards) users complain that under Linux their cards run at only
>about
>700Mhz core speed instead of 1Ghz. What is your experience with GTX 680?
>I was also wondering whether the GTX680 use the
>boost clock during the Amber calculations or the just the base one?
>
I think this is just speculation. When you run AMBER with a GTX680 it
prints the following:
|------------------- GPU DEVICE INFO --------------------
|
| CUDA Capable Devices Detected: 1
| CUDA Device ID in use: 0
| CUDA Device Name: GeForce GTX 680
| CUDA Device Global Mem Size: 2047 MB
| CUDA Device Num Multiprocessors: 8
| CUDA Device Core Freq: 0.71 GHz
|
|--------------------------------------------------------
But this is a query that occurs at the very beginning of a run before any
CUDA kernels have been run. I believe that when unloaded the 680 in Linux
clocks down to 705MHz to save power. When you stress it hard it
automatically clocks up the frequency. I am not sure if there is way to
check this though while the card is under load. Certainly the performance
we see would be what it is if the clock speed was only 705MHz. I am asking
NVIDIA engineering to clarify though.
>Finally, what is the performance difference of
>pmemdCuda under Linux and Cygwin?
Never tried and I very much doubt you'll be able to get pmemd.cuda
compiled under cygwin. Cygwin emulates things through the cygwin dll and
so you'd need a cygwin compatible version of the nvidia compiler I'd
expect.
Note have a native Windows version of pmemd.cuda but never released the
binary since the performance is about half that of what it is on Linux due
to a bug in cuda 4.2 under windows that limited performance. cuda 3 showed
good performance under windows but you can't use that with AMBER 12. We
haven't had time to get back to looking at this with cuda 5 unfortunately.
All the best
Ross
/\
\/
|\oss Walker
---------------------------------------------------------
| Assistant Research Professor |
| San Diego Supercomputer Center |
| Adjunct Assistant Professor |
| Dept. of Chemistry and Biochemistry |
| University of California San Diego |
| NVIDIA Fellow |
|
http://www.rosswalker.co.uk |
http://www.wmd-lab.org |
| Tel: +1 858 822 0854 | EMail:- ross.rosswalker.co.uk |
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Received on Fri Feb 22 2013 - 21:00:03 PST
