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MM5 performance on AMD64 Opteron
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Jesse



Joined: 27 Jul 2004
Posts: 4

PostPosted: Wed Oct 27, 2004 2:26 pm    Post subject: MM5 performance on AMD64 Opteron Reply with quote

I lately compared the cpu time between Xenon and AMD64 in running MM5 codes (compiled on PGI 5.2), and found that the speed up was merely 1.4 times. Although the Xenon chip has a clock rate 2.8GHz faster than the AMD64 at 1.8GHz, I would expect the benefit of using 64 bits will still triumph a faster 32bit chips by a large margin.

I wonder if there's any problem with my optimization setting or the environment? I am using the configure.user file provided in the "tips and resource" for compiling the AMD64/MM5 on Federa Linux. Do I need to use other Linux favor such as SuSE?

Any input will be greatly appreciated!

PS I also have other problems with compiling other modules of MM5 on AMD64/PGI fortran. May post my questions later ...
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mkcolg



Joined: 30 Jun 2004
Posts: 6134
Location: The Portland Group Inc.

PostPosted: Thu Oct 28, 2004 11:21 am    Post subject: Reply with quote

Hi Jesse,


The only thing a 64-bit system can guarantee you is that it can handle larger problem sizes. A 64-bit system should at the very least have the same performance as a 32-bit executable running on the same system. Some codes will see a performance benefit, and while rare, others actually degrade.

I just ran MM5 on a 1600 Mhz Dual CPU AMD Opteron running SuSE9.1 using both a 64-bit and 32-bit executable. The 64-bit executable took 144 seconds while the 32-bit took 148 seconds. Some performance benefit, but not much.

To better compare the Xeon and the AMD64, I'd run the Xeon's MM5 executable on the AMD64. Comparing this result to the 64-bit executable's result should give you a better idea of what amount of the performance increase can be attributed to 64-bits. Comparing the two 32-bit results will show what portion of the speed-up is due to differences between the two systems.

Please feel free to ask questions about the problems your having with the MM5 modules. I'm not an expert in building these modules, but we should be able to work through each problem. I'm sure if your encountering a problem, others are as well.

- Mat
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Jesse



Joined: 27 Jul 2004
Posts: 4

PostPosted: Wed Nov 17, 2004 11:38 am    Post subject: Reply with quote

I tried your suggestions but failed to run the codes. For example, I compiled MM5 on Xenon and transported them to opteron for a trial run, which failed. The Xenon machine runs on redHat Linux 9 whilst the opteron sits on federa linux. Both have pgi 5.2-4 fortran.

While it is interesting to compare xenon and amd, but I am most concerned with compiling and running mm5 codes. I encountered quite a bit of problems. First, I have some problem with NCAR Graphics. Then I tried to compile the MM5/TERRAIN module without ncargraphics. The compilation apparently succeeded but the codes always fail with segmentation fault. Can you help?

Best regards
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mkcolg



Joined: 30 Jun 2004
Posts: 6134
Location: The Portland Group Inc.

PostPosted: Wed Nov 17, 2004 1:26 pm    Post subject: Reply with quote

Hi Jesse,


Granted it's not about TERRAIN, but we have created a guide to building and running MM5 (see http://www.pgroup.com/resources/isv.htm#MM5) which might help.

MM5 uses a lot of stack space, so usually when MM5 seg faults it's because of a stack overflow. To correct, set your stack size to unlimited (check your shell docs for the specific command to increase your stack space. On csh its 'unlimit').

The second cause is forgetting to add "-Mbyteswapio -Mnosgimp" and in 64-bits "-DDEC_ALPHA". Adding "-DDEC_ALPHA" in 32-bits will also cause a seg fault.

I've only built the NCAR Graphics library and TERRAIN once but don't remember the issues (its been awhile). I'll try it again and log what I do.

- Mat
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Jesse



Joined: 27 Jul 2004
Posts: 4

PostPosted: Wed Nov 17, 2004 2:09 pm    Post subject: Reply with quote

Yes, please post your log after coming back from testing ncarg and terrain. In particular, I want to know if one should compile these modules as 32bit or 64bit on opteron?

My compilation problems are with the other MM5 modules, not MM5 itself. Since there are so many modules, I want to resolve them one at a time. Your experience with ncarg and terrain will be helpful.

Great thanks for your prompt response!
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