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346gnu13-Aquamarine
13-Aquamarine
October 8, 2012
Question

LDA, Only one core used?

  • October 8, 2012
  • 3 replies
  • 6828 views

Creo Simulate. Large deflection analysis with contact.

Can anyone help me understand why is appears that only 1 core's worth of cpu is doing all the work (11 others available)?

Thanks


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3 replies

J
JonathanHodgson13-Aquamarine
13-Aquamarine
October 8, 2012

Hi Charles,

I don't run many contact or LDA analyses, but from my experience with static analysis I suspect there are two reasons:

  1. Certain stages of the analysis cannot be split up. Meshing is the first one; then to solve the matrix, one core has to 'supervise' both dividing the job for multiples cores, and the re-combining the results. Actually writing the results to disk is also a single-core task; so it's only really the matrix solve that runs on multiple cores.
  2. The limiting factor may be hard drive speed, in which case even if multiple cores are working they may all be waiting for temporary file access, giving a net usage no higher than one core.

We've had great success speeding up Mechanica by installing the maximum memory (24 GB) in our machines (don't forget to set Mechanica to use 8192 MB) and putting both temporary files and results onto a 6 GB RAM disk. (For very large models, writing the results can take a long time, so if you can't create a RAM disk big enough for both temp files and results, test it with temp files on the hard drive and results on the RAM disk, as well as the other way round. Or buy an SSD...)

Running with lots of memory and a RAM disk, we now frequently see "CPU time" much greater than "Elapsed time" in the run summary file. This wasn't generally possible when writing data to a hard disk.

HTH,

Jonathan

J
JonathanHodgson13-Aquamarine
13-Aquamarine
October 8, 2012

Other useful pointers on SOLRAM setting, etc., in this thread:

http://communities.ptc.com/message/183371#183371

3
346gnu13-AquamarineAuthor
13-Aquamarine
October 9, 2012

Thanks,

For hardware, we are reasonably well set up with RAM and fast striped disks etc. It's not hardware.

Possibilities I pondered included :

  • software architecture (not yet rewritten for multi-core)
  • bought in LDA solver technology licensing limitation.

My 48 hour study would take roughly (and I know some allowance for time to poke tasks at various cpu's is required) about 4 hours?

I must have missed a trick.

J
jreeh1-Visitor
1-Visitor
December 30, 2014

I am a bit new to this. However we are in the same boat. I am running an analysis on a silicone seal which obviouslly has a very large deformation (non-linear). The seal material is also non-linear and the model also has several contacts. I simplified the model as much as I could however the element count is still arount 15,000.

The model does run properly, however it takes 6 days and I am still not at the full displacement yet.

Right now we are considering building a new computer forhis purpose. Since it is obvious that the majority of the run takes place on one processer we are evaluating the two folloing options:

Intel Core i7-5820K

Intel Core i7-4790K

I am currently using this one:

Intel Xeon E5640

Does anyone have expiriance with these two or perhaps other suggestions?

We are also considering a few SSDs in a RAID and about 16 GB of DDR3 memory.

However, what I would really like to know is what type of gains may I expect. If shave the 6 days down to 4 I havent really gained all that much. However a 5x increase in speed wbe worth it.

Any comments?

3
346gnu13-AquamarineAuthor
13-Aquamarine
December 30, 2014

Some useful info here

http://communities.ptc.com/message/266735#266735

For single core processes such as LDA get the fastest single core cpu possible.

Regards

J
jreeh1-Visitor
1-Visitor
December 30, 2014

We have implemented a ramdisk via IMdisk on the same computer and it increased the speed by 5 fold!

10 minute iterations are now only taking 2 minutes!

Amazing!

However the CPU load only increased from 25% to 30% suggesting that there is still a bottle neck somewhere and more room for improvements.

However, I should have enough ammution to go for a computer upgrade with faster RAM and more of it...

J
JonathanHodgson13-Aquamarine
13-Aquamarine
January 5, 2015

Hi Jonathan,

Glad to hear the RAM disk solution helped!

However, I suspect that the remaining 'bottleneck' is that you have three out of four cores sitting mostly idle; as discussed at the beginning of this thread, LDA seems only to use one core.

Faster RAM is now unlikely to help you much (I'd expect a percentage improvement only) although more of it will allow a larger RAM disk and therefore solving larger analyses. A faster (single-thread score) CPU will also help - your E5640 looks pretty slow at 1166 (we're disposing of workstations with faster processors than that here), so replacing with an i7-4790k at over 2500 should double the speed, or even more. The 5820 is a little slower, around 2000, but depending on the price you may decide that's a more sensible route.

As a wildcard, if cost matters and you're sure don't need multi-thread power, consider a fast i3 or even a Pentium - I've recently upgraded my home gaming rig with a Pentium G3258 which was just £50 (CPU and cooler) and scores well over 2000, whilst a 4790k currently goes for over £250... Also note that the "k" is strictly speaking unnecessary unless you plan on overclocking.

Cheers,

another Jonathan

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