#331532 - QUESTION: In HF analysis, the computation run time for 8.0 ismuch slower then 6.1 widely. Why does this happen and is there aworkaround? ANSWER: We found 2 sources of the performance difference.One is solver related; the other is related to element 120. I can tell youhow to fix the solver issue and I'll forward this information to the elementdeveloper for comment on the performance of el120. After 6.1 we startedoptimizing memory usage for the solvers. The intent was to try and runproblems in memory ( incore ) rather than out-of-core whenever possible.Indeed, your 8.1 run was incore while the 6.1 run ran out-of-core. Butthere is a gotcha with incore runs. ANSYS allows multiple loads with thesame factorization. To do this we save the sparse solver workspace so thaton subsequent loads, as soon as we determine that the boundaryconditions are identical we can resume the sparse solver and just do aforward/backward solve. This is much cheaper than doing 2 factorizations.For an out-of-core run the matrix factor is already sitting in a file so all wehave to save is the rest of the sparse solver work array. But, in an incorerun when we save the solver work array we end up saving the whole factoras well. The I/O to do this is very slow on Windows. The way to avoid thisis to use an undocumented option in the bcsopt command. The tests thatwe ran using this option made a huge difference in solver time. Add this toyour input before the solve command: bcsopt,,,,-1,,-5 - That's 4 commas, a-1 , and then 2 more and a -5. The -5 is there for performance debug. The-1 surpresses writing that LN22 file for backup of the workspace. Anotherway to get this done is to tell the solver to run in optimal out-of-core moderather than incore.. to do this use bcsopt,,opti,,,,-5 I tried both solutionsand got about the same results. Incore was faster but both were nowcompetitive with the 6.1 results. We also noticed that version

Family: Structural MechanicsProduct: Mechanical APDL (f. ANSYS)Version: 8.0Area: Multiphysics and EMAG (APDL)Subarea: Low Frequency

Answer:

QUESTION:

In HF analysis, the computation run time for 8.0 is much slower then 6.1 widely. Why does this happen and is there aworkaround?

ANSWER:

We found 2 sources of the performance difference.One is solver related; the other is related to element 120. I can tell you how to fix the solver issue and I'llforward this information to the element developer for comment on the performance of el120.

After 6.1 we started optimizing memory usage for the solvers. The intent was to try and run problemsin memory ( incore ) rather than out-of-core whenever possible. Indeed, your 8.1 run was incorewhile the 6.1 run ran out-of-core. But there is a gotcha with incore runs. ANSYS allows multiple loads with the samefactorization. To do this we save the sparse solver workspace so that on subsequent loads, as soon as wedetermine that the boundary conditions are identical we can resume the sparse solver and just doa forward/backward solve. This is much cheaper than doing 2 factorizations. For an out-of-core run the matrixfactor is already sitting in a file so all we have to save is the rest of the sparse solver work array. But, in

QUESTION:<br><br>In HF analysis, the computation run time for 8.0 ... https://www1.ansys.com/onyxkb/solutions-cust/ssoc331532.htm

1 z 2 12.1.2012 10:27

an incore run when we save the solver work array we end up saving the whole factor as well. The I/Oto do this is very slow on Windows. The way to avoid this is to use an undocumented option in the bcsopt command.The tests that we ran using this option made a huge difference in solver time. Add this to yourinput before the solve command:

bcsopt,,,,-1,,-5 - That's 4 commas, a -1 , and then 2 more and a -5. The -5 is there for performancedebug. The -1 surpresses writing that LN22 file for backup of the workspace.

Another way to get this done is to tell the solver to run in optimal out-of-core moderather than incore.. to do this use

bcsopt,,opti,,,,-5

I tried both solutions and got about the same results. Incore was faster but both were nowcompetitive with the 6.1 results. We also noticed that version7.1 of ANSYS ran the sparse complexsolver faster than 8.0. But it is still comparable with 6.1, even as is.

The other performance problem is that in writing the element results the time for el120 has significantly increased.In 6.1 we got this..

8 hLSSet2 76416 0.297 0.000004 0.00 0.000 1.008 el120 7641628.328 0.000371 29.00 0.000 1.008 elnfor 76416 0.375 0.000005 0.00 0.000 1.008 elenrg 76416 0.594 0.000008 1.00 0.000 1.00

In 8.1 we got this timing of the el120 element..

8 hLSSet2 76416 0.250 0.000003 0.00 0.000 1.008 el120 76416 118.656 0.001553 0.00 0.000 1.008 elnfor 76416 0.781 0.000010 0.00 0.000 1.008 elenrg 76416 0.484 0.000006 0.00 0.000 1.00

For now, I'd recommend trying either of the bcsopt solutions described above.

QUESTION:<br><br>In HF analysis, the computation run time for 8.0 ... https://www1.ansys.com/onyxkb/solutions-cust/ssoc331532.htm

2 z 2 12.1.2012 10:27