General guidelines for long transient simulations
Eddy Wu
The circuit has ~17K unknowns. I've roughly followed the optimizations in the Xyce reference manual and in this forum.
- no floating nodes
- reduced timeint tolerances
- linsol=klu
- integration method = trap
The majority of the simulation time is in the transient analysis. I am using an Intel Xeon E7-8880 V4, and 32 slots in Xyce parallel (tried from 2-32 slots and serial build).
What I'm seeing is the best case scenario I am only able to achieve 12us transient sim per hour of simulation time.
Are there any other options I can try to improve simulation performance?
Thanks,
Eddy
Marcel Hendrix
xyce-users
weiji
If you compile the software yourself, you can try using the MUMPS solver to solve linear equations in parallel. From our experience, MUMPS has pretty good solving efficiency when running on a single computer node. However, by default, Xyce does not enable MUMPS support. First, you need to have a Trillinos library that supports MUMPS, then recompile Xyce and manually enable MUMPS support. This can be a challenging job. Good luck to you!
Eddy Wu
Regarding Marcel's comments, I am only saving a few nodes so I am not going to be memory limited. I'd ideally like to run my entire block in simulation at least once without reductions.
Eric, I am doing parallel load, serial solve. 99% of the time is spent in the "Beignning Tranisent Calculation ... " phase.
- I believe I am doing parallel load, serial solve. I am doing an mpirun of xyce with .options linsol type=klu set.
- I've tried the .options output initial_interval; however, that will either truncate my signal, or generate more data than leaving it unset. I lose some accuracy on the clocked edges, but I can probably manage. I would typically set this options to <0.5 max transient step. I'm managing file size by only printing out a few nodes.
Weiji,
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Mehmet Cirit
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xyce-users
Thanks for the information. It does sound like you are doing the "parallel load serial solve" option with type=klu.
Regarding the "multiple options" for output intervals, they are not supposed to overlap. Basically you can set different output intervals for different windows of time. So, if you know that certain windows don't have much happening, you could set a course output and for others which have more activity set a finer output. And, yes, I'm just referring to the options described on page 157 of the guide. I mis-spoke a bit about setting up multiple "options output" statements, since you can set multiple intervals on a single line.
BTW, speaking of max time steps, you can also set different max time steps at different time windows as well, using the "schedule" command on the tran line. It looks something like this: .tran 0 2.0e-3 {schedule( 0.5e-3, 0, 1.0e-3, 1.0e-6, 1.5e-3, 1.0e-4, 2.0e-3, 0 )}
Regarding solvers like MUMPS, I would be curious to see some timing comparisons as well. I've been aware of MUMPS for a long time, but the last time we tried it (a long time ago) it didn't perform that well. But possibly it has improved.
More broadly, there are more solvers available (including MUMPS, but also others) if you are willing to build Trilinios and Xyce yourself. One example is the Pardiso solver (a threaded direct solver), which has worked well for us on some very large circuits (much larger than 17k). Another possibility is the BASKER solver which is a Sandia-developed threaded direct solver. I generally wouldn't expect any of these solvers to perform better than KLU for a problem size this small. By parallel computing standards, 17k is not very large. We usually only bother with parallel solvers (of any variety) when the problem size is in the 100s of thousands of unknowns or more.
If the main problem with your calculation is the DCOP phase (and it sounds like it might be), then you could save (via .SAVE) the DCOP result from one calculation, and then use it for subsequent calculations.
Another thing you could do to speed up the simulation would be to use a different step-size selection strategy. I generally don't recommend using this unless you are desperate, but you can get much larger time steps by setting .OPTIONS TIMEINT ERROPTION=1 . Setting this turns off the local truncation error based time step size control, and replaces it with a step size strategy based on the success/failure of the nonlinear solver. You can read about this on page 77 of the guide. Doing this (ERROPTION=1) will almost certainly result in a less accurate transient calculation. But, the transient phase of a calculation will usually be much faster as the stepsizes will be larger.
thanks,
Eric
xyce-users
XYCE
Hi Eddy,
It is hard to give suggestions without knowing some simulation details of your circuit. Is your circuit running slow because Xyce is taking too many steps or it is because each step is very expensive, or Xyce output is taking too much time? You can shorten your simulation and look at the Timing statics of Xyce run at the end of the simulation. It tells you how many accepted/failed steps Xyce takes, and how much time Xyce spends on device evaluation, linear solver, etc..
How many time steps for each clock cycle in your simulation? If it is too many, look at the waveform to see if it indicates any stability issues (for example, artificial point-to-point ringing). If so and if you circuit is not autonomous (oscillators), you can try a more stable time integrator gear by using:
.options timeint method=gear
Or if you need an even more stable method (BE), use
.options timeint maxord=1
These options would normally take care of the stability related performance issue. See Xyce user’s guide 7.3.4 for details.
In addition to Eric’s suggestion to turn off local truncation error (LTE) control, you can also try different local truncation error control by setting newlte in the timeint option. Some newlte option is more aggressive and is well suited for digital circuits. See Xyce user’s guide 7.3.5.
If Xyce takes reasonable number of step per clock cycle, see if any part, such as device evaluation or linear solver, is taking large part of the run time.
You mentioned that most of time is spent at the beginning transient calculation phase, it suggests that Xyce is taking a lot of time steps at the beginning of the simulation (relative to the length of the simulation).
If you would like us to take a look at your circuit and simulation, please feel free to send the circuit for us to debug. Please send it to xyce-de...@sandia.gov. Not all of us get emails from google group.
Thanks,
Ting
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Eddy Wu
Thanks again for all the feedback.
@mehmet: with or without parasitic RC values does impact the simulation, but I didn't notice an appreciable difference. I also do not include any small RC values.
Question 1) what do you mean full stack of instance parameters? Are you referring to the transistor library files?
@Eric: Thanks for the description of transient schedule. I'm looking into trying other direct solvers in the trilinos package.
Question 2) Are there any guidelines on adding solvers that are not in the example reconfigure file? (ex add -DTrilinos_ENABLE_<solver>=ON or -DAmesos_ENABLE_<solver>=ON)
- with regards to the DCOP, the majority of the time is spent in Transient stepping. A small portion of the time is spent in DCOP. Below is a summary section of a shorter simulation
- I tried the .options timeint erroption=1 method with mixed results. For this particular simulation I didn't notice an appreciable difference.
@ting:
- I think each step is too expensive.
- I've attached a snapshot of one clock cycle of the simulation.
- I've found the options timeint method=gear gave slower output in general. To my untrained eye, it doesn't appear to have significant ringing per the snapshot below.
- I've looked through section 7.3.5 and trying out .options newlte=2 made the simulation slightly slower. Note: I am also setting abstol reltol=1e-2 on the same line.
- Thank you for your offer for help. I'm looking into how I can best send you a file. I am looking to see if I can recreate this issue with a different library, one which we would both have access to.
***** Problem read in and set up time: 1.23625 seconds
***** DCOP time: 17.8228 seconds. Breakdown follows:
Number Successful Steps Taken: 1
Number Failed Steps Attempted: 0
Number Jacobians Evaluated: 1568
Number Linear Solves: 1568
Number Failed Linear Solves: 0
Number Residual Evaluations: 1607
Number Nonlinear Convergence Failures: 0
Total Residual Load Time: 9.64767 seconds
Total Jacobian Load Time: 2.62472 seconds
Total Linear Solution Time: 4.42902 seconds
***** Transient Stepping time: 1171.27 seconds. Breakdown follows:
Number Successful Steps Taken: 14563
Number Failed Steps Attempted: 478
Number Jacobians Evaluated: 86929
Number Linear Solves: 86929
Number Failed Linear Solves: 0
Number Residual Evaluations: 101970
Number Nonlinear Convergence Failures: 471
Total Residual Load Time: 685.049 seconds
Total Jacobian Load Time: 160.085 seconds
Total Linear Solution Time: 255.508 seconds
***** Solution Summary *****
Number Successful Steps Taken: 14564
Number Failed Steps Attempted: 478
Number Jacobians Evaluated: 88497
Number Linear Solves: 88497
Number Failed Linear Solves: 0
Number Residual Evaluations: 103577
Number Nonlinear Convergence Failures: 471
Total Residual Load Time: 694.697 seconds
Total Jacobian Load Time: 162.709 seconds
Total Linear Solution Time: 259.937 seconds
***** Total Simulation Solvers Run Time: 1189.09 seconds
***** Total Elapsed Run Time: 1190.33 seconds
*****
***** End of Xyce(TM) Simulation
*****
Timing summary of processor 0
Stats Count CPU Time Wall Time
---------------------------------------- ------ --------------------- ---------------------
Xyce 1 19:44.645 (100.0%) 19:50.599 (100.0%)
Analysis 1 19:43.433 (99.90%) 19:49.090 (99.87%)
Transient 1 19:43.432 (99.90%) 19:49.090 (99.87%)
Nonlinear Solve 15042 18:58.688 (96.12%) 19:02.271 (95.94%)
Residual 103577 11:32.958 (58.49%) 11:35.302 (58.40%)
Jacobian 88497 2:42.049 (13.68%) 2:42.937 (13.69%)
Linear Solve 88497 4:19.536 (21.91%) 4:20.128 (21.85%)
Successful DCOP Steps 1 0.041 (<0.01%) 0.191 ( 0.02%)
Successful Step 14563 39.852 ( 3.36%) 41.748 ( 3.51%)
Failed Steps 478 0.002 (<0.01%) 0.002 (<0.01%)
Nonlinear Failure 471 0.000 (<0.01%) 0.000 (<0.01%)
Netlist Import 1 0.926 ( 0.08%) 0.962 ( 0.08%)
Parse Context 1 0.162 ( 0.01%) 0.165 ( 0.01%)
Distribute Devices 1 0.706 ( 0.06%) 0.729 ( 0.06%)
Verify Devices 1 0.000 (<0.01%) 0.000 (<0.01%)
Instantiate 1 0.021 (<0.01%) 0.026 (<0.01%)
Late Initialization 1 0.254 ( 0.02%) 0.261 ( 0.02%)
Global Indices 1 0.034 (<0.01%) 0.034 (<0.01%)
Setup Matrix Structure 1 0.015 (<0.01%) 0.017 (<0.01%)
Timing summary of 8 pr
Time CPU Wall Time
Statsf System) Max (% oMax (% of System)
--------------------------------- -----------------------------
Xyce 46 (12.48%) 19:46.9 19:50.600 (12.50%)
Analysis 33 (12.47%) 19:45.7 19:49.090 (12.48%)
Transient 32 (12.47%) 19:45.7 19:49.090 (12.48%)
Nonlinear Solve 88 (12.00%) 18:59.2 19:02.302 (11.99%)
Residual 58 ( 7.30%) 11:33.5 11:35.566 ( 7.30%)
Jacobian 86 ( 1.69%) 2:42.0 2:42.937 ( 1.71%)
Linear Solve 36 ( 2.73%) 4:21.3 4:21.994 ( 2.75%)
Successful DCOP 41 (<0.01%) 0.1 0.191 (<0.01%)
Successful Step 34 ( 0.40%) 39.8 41.748 ( 0.44%)
Failed Steps 02 (<0.01%) 0.0 0.002 (<0.01%)
Nonlinear Fail00 (<0.01%) 0.0 0.000 (<0.01%)
Netlist Import 26 (<0.01%) 0.9 0.962 ( 0.01%)
Parse Context 62 (<0.01%) 0.1 0.165 (<0.01%)
Distribute Devices06 (<0.01%) 0.7 0.729 (<0.01%)
Verify Devices 00 (<0.01%) 0.0 0.000 (<0.01%
Instantiate 12 (<0.01%) 0.0 0.026 (<0.01%)
Late Initialization 54 (<0.01%) 0.2 0.267 (<0.01%)
Global Indices 34 (<0.01%) 0.0 0.040 (<0.01%)
Setup Matrix Structu15 (<0.01%) 0.0 0.018 (<0.01%)
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xyce-users
xyce-users
Eddy Wu
Thanks for the quick response. I ran with .options dist strategy=2 (all other parameters the same) and found the transient step time to be about 5% better. Below is the xyce summary output below:
***** Problem read in and set up time: 1.57195 seconds
***** DCOP time: 17.9227 seconds. Breakdown follows:
Number Successful Steps Taken: 1
Number Failed Steps Attempted: 0
Number Jacobians Evaluated: 1568
Number Linear Solves: 1568
Number Failed Linear Solves: 0
Number Residual Evaluations: 1607
Number Nonlinear Convergence Failures: 0
Total Jacobian Load Time: 2.64314 seconds
Total Linear Solution Time: 4.58896 seconds
***** Transient Stepping time: 1100.66 seconds. Breakdown follows:
Number Successful Steps Taken: 14563
Number Failed Steps Attempted: 478
Number Jacobians Evaluated: 86929
Number Linear Solves: 86929
Number Failed Linear Solves: 0
Number Residual Evaluations: 101970
Number Nonlinear Convergence Failures: 471
Total Jacobian Load Time: 149.585 seconds
Total Linear Solution Time: 243.285 seconds
***** Solution Summary *****
Number Successful Steps Taken: 14564
Number Failed Steps Attempted: 478
Number Jacobians Evaluated: 88497
Number Linear Solves: 88497
Number Failed Linear Solves: 0
Number Residual Evaluations: 103577
Number Nonlinear Convergence Failures: 471
Total Jacobian Load Time: 152.228 seconds
Total Linear Solution Time: 247.874 seconds
***** Total Simulation Solvers Run Time: 1118.59 seconds
***** Total Elapsed Run Time: 1120.16 seconds
*****
***** End of Xyce(TM) Simulation
*****
Timing summary of processor 0
Stats Count CPU Time Wall Time
---------------------------------------- ------ --------------------- ---------------------
Analysis 1 18:33.934 (99.86%) 18:38.586 (99.84%)
Transient 1 18:33.934 (99.86%) 18:38.586 (99.84%)
Nonlinear Solve 15042 17:52.286 (96.13%) 17:55.055 (95.95%)
Residual 103577 10:51.834 (58.43%) 10:53.686 (58.34%)
Jacobian 88497 2:31.782 (13.61%) 2:32.450 (13.61%)
Linear Solve 88497 4:07.512 (22.19%) 4:08.008 (22.14%)
Successful DCOP Steps 1 0.041 (<0.01%) 0.209 ( 0.02%)
Successful Step 14563 37.061 ( 3.32%) 38.754 ( 3.46%)
Failed Steps 478 0.002 (<0.01%) 0.002 (<0.01%)
Nonlinear Failure 471 0.000 (<0.01%) 0.000 (<0.01%)
Parse Context 1 0.136 ( 0.01%) 0.137 ( 0.01%)
Distribute Devices 1 1.169 ( 0.10%) 1.192 ( 0.11%)
Verify Devices 1 0.000 (<0.01%) 0.000 (<0.01%)
Late Initialization 1 0.170 ( 0.02%) 0.175 ( 0.02%)
Global Indices 1 0.028 (<0.01%) 0.028 (<0.01%)
Setup Matrix Structure 1 0.012 (<0.01%) 0.012 (<0.01%)
Timing summary of 8 processors
CPU Time CPU Time CPU Time Wall Time Wall Time Wall Time
Stats Count Sum (% of System) Min (% of System) Max (% of System) Sum (% of System) Min (% of System) Max (% of System)
---------------------------------------- ------ --------------------- --------------------- --------------------- --------------------- --------------------- ---------------------
Xyce 8 2:28:54.731 (100.0%) 18:35.497 (12.48%) 18:37.234 (12.50%) 2:29:23.275 (100.0%) 18:40.406 (12.50%) 18:40.414 (12.50%)
Analysis 8 2:28:42.121 (99.86%) 18:33.934 (12.47%) 18:35.652 (12.49%) 2:29:08.688 (99.84%) 18:38.586 (12.48%) 18:38.586 (12.48%)
Transient 8 2:28:42.119 (99.86%) 18:33.934 (12.47%) 18:35.652 (12.49%) 2:29:08.687 (99.84%) 18:38.586 (12.48%) 18:38.586 (12.48%)
Nonlinear Solve 120336 2:22:57.820 (96.01%) 17:51.687 (11.99%) 17:52.492 (12.00%) 2:23:20.230 (95.95%) 17:54.867 (11.99%) 17:55.099 (11.99%)
Residual 828616 1:26:54.963 (58.37%) 10:51.528 ( 7.29%) 10:52.033 ( 7.30%) 1:27:09.629 (58.35%) 10:53.656 ( 7.29%) 10:53.753 ( 7.29%)
Jacobian 707976 20:07.461 (13.51%) 2:29.162 ( 1.67%) 2:31.957 ( 1.70%) 20:13.145 (13.53%) 2:29.850 ( 1.67%) 2:32.793 ( 1.70%)
Linear Solve 707976 33:06.263 (22.23%) 4:07.257 ( 2.77%) 4:09.939 ( 2.80%) 33:10.374 (22.21%) 4:07.700 ( 2.76%) 4:10.634 ( 2.80%)
Successful DCOP Steps 8 1.501 ( 0.02%) 0.041 (<0.01%) 0.209 (<0.01%) 1.673 ( 0.02%) 0.209 (<0.01%) 0.209 (<0.01%)
Successful Step 116504 4:44.171 ( 3.18%) 34.690 ( 0.39%) 37.061 ( 0.41%) 4:48.028 ( 3.21%) 34.972 ( 0.39%) 38.754 ( 0.43%)
Failed Steps 3824 0.018 (<0.01%) 0.002 (<0.01%) 0.002 (<0.01%) 0.017 (<0.01%) 0.002 (<0.01%) 0.002 (<0.01%)
Nonlinear Failure 3768 0.002 (<0.01%) 0.000 (<0.01%) 0.000 (<0.01%) 0.002 (<0.01%) 0.000 (<0.01%) 0.000 (<0.01%)
Netlist Import 8 11.024 ( 0.12%) 1.362 ( 0.02%) 1.384 ( 0.02%) 11.112 ( 0.12%) 1.389 ( 0.02%) 1.389 ( 0.02%)
Parse Context 8 1.091 ( 0.01%) 0.135 (<0.01%) 0.137 (<0.01%) 1.093 ( 0.01%) 0.136 (<0.01%) 0.137 (<0.01%)
Distribute Devices 8 9.499 ( 0.11%) 1.169 ( 0.01%) 1.191 ( 0.01%) 9.538 ( 0.11%) 1.192 ( 0.01%) 1.192 ( 0.01%)
Verify Devices 8 0.000 (<0.01%) 0.000 (<0.01%) 0.000 (<0.01%) 0.000 (<0.01%) 0.000 (<0.01%) 0.000 (<0.01%)
Instantiate 8 0.116 (<0.01%) 0.012 (<0.01%) 0.018 (<0.01%) 0.141 (<0.01%) 0.017 (<0.01%) 0.019 (<0.01%)
Late Initialization 8 1.390 ( 0.02%) 0.170 (<0.01%) 0.176 (<0.01%) 1.413 ( 0.02%) 0.175 (<0.01%) 0.177 (<0.01%)
Global Indices 8 0.235 (<0.01%) 0.028 (<0.01%) 0.030 (<0.01%) 0.236 (<0.01%) 0.028 (<0.01%) 0.030 (<0.01%)
Setup Matrix Structure 8 0.096 (<0.01%) 0.012 (<0.01%) 0.012 (<0.01%) 0.097 (<0.01%) 0.012 (<0.01%) 0.012 (<0.01%)
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XYCE
Hi Eddy,
Thanks for providing the timing statistics and snapshot of some waveforms. It gives more information about the simulation.
The 3rd picture shows typical point-to-point ringing during the sharp transition (red waveform). This indicates stability issue. If gear does not fix the problem, try more stable method BE (maxord = 1). It should quickly damp out the overshooting. How many time steps Xyce takes on average for a clock cycle in your simulation?
BTW, loosening the tolerance may not always be a good idea to speedup a simulation. It could work in some cases. But it could also make the artificial point-to-point ringing worse for Trap method. The ringing is due to marginal stability of Trap method. Small numerical error can cause ringing and a loose tolerance can make it worse. In general, we should be careful if we loosen reltol in the simulation.
From timing statistics, you can see that majority of the time is spent on device evaluation (residual and Jacobian) and it takes more than 70% of the simulation time. The linear solver only takes about 22%. What device models are you using? You can get the information from the Device Count Summary at the beginning of the simulation. We have seen efficiency problems in device evaluations for certain devices due to different reasons previously and have fixed some of them. Please let us know and we will see if there is any efficiency problem in device evaluation. Could you also provide all the options lines you used in the simulation if you cannot send us the netlist.
Also, with a fast clock cycle and a long simulation length, the simulation has about 1.28 million cycles. According to the current timing statics, we can estimate how much time each step takes. Even with a reasonable number of time steps per cycle, the simulation is going to take many hours. Why do you need such a long simulation length? Does the circuit have some slow behavior that is orders of magnitude slower than the clock speed? If so, a plain transient simulation is not well suited for this case. Advance simulation methods, such as envelope methods normally available in RF simulators (e.g., Spectre RF), would be much faster in this case.
Thanks,
Ting
From: Eddy Wu <ed...@imagica.technology>
Sent: Friday, January 12, 2024 12:39 PM
To: XYCE <XY...@sandia.gov>
Cc: xyce-users <xyce-...@googlegroups.com>
Subject: [EXTERNAL] Re: [xyce-users] Re: General guidelines for long transient simulations
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Eddy Wu
XYCE
Hi Eddy,
Thanks for the update. Yes. Using tighter tolerance with Trap method would reduce artificial ringing. Using a more stable method (gear, BE) is another way to reduce ringing. With the same tolerance, a more stable method should have less ringing. This is briefly mentioned in Xyce users’ guide and Kundert’s paper has more detailed explanation.
According to new information you provide here, the number of time steps per cycle is already reasonable. The artificial ringing led to some unnecessary steps at the sharp transition, but it damps out.
I assume that you use level 9 MOSFET in Xyce which is BSIM3. It is a hand written model and we have not seen performance related issue for device evaluation in this model previously. What other devices are used in the simulation? I wonder why >70% time is spent in device evaluation even with dist strategy=2.
Most simulation options are fine. Some minor things. The abstol of 1e-2 is too loose. The default is 1e-6. But abstol has a much less effect in LTE than reltol. Do you have a lot of floating nodes? The two addresistor preprocess lines are not used in this netlist. These commands in this netlist will generate another netlist with the name _xyce.cir which contains extra resistors added to the floating nodes. You will need to run _xyce.cir if you would like these extra resistors.
Thanks for explaining the reason why you need a long simulation length. With 1.28 million cycles, the simulation would have lots of output. I did a quick estimation with 100 time step per cycle. Your simulation is going to take a few months according to the current timing statistics.
Since the number of time steps per cycle is reasonable in your simulation, the main way to improve performance is to see if the cost per step can be reduced. As I mentioned before, the device evaluation takes >70% run time and linear solver takes 22%. Improving them would improve performance, but device evaluation would have a larger impact. Or it is possible that there may not be much performance issue, the simulation is slow because there are so many cycles. It is a limitation of plain transient simulation for the circuit.