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cmos.analogvala

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Spectre +turbo Simulations slower than Spectre Simulations
May 16^th, 2010, 11:26pm

I have been trying to reduce simulation time of my netlist for quite some time.

I tried many things from moving to MMSIM to reducing netlist itself. We came to know that with Spectre +turbo simulations can run faster.

We tried to simulate a long netlist using spectre and spectre +turbo. on the same OS and the same machine. We found that Spectre +turbo was slower than spectre. From the log file it appears that spectre+turbo is taking very small steps, hence it's slower than spectre.

Any clues why so ? Is there a way to improve step size of spectre + turbo simulations? Is there any other way of getting faster results without compromising accuracy ?

Thanking You,
CA

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Marq Kole

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Hmmm. That's
weird...

Posts: 122
Eindhoven, The Netherlands

Re: Spectre +turbo Simulations slower than Spectre Simulations
Reply #1 - May 26^th, 2010, 2:58pm

What Spectre +turbo does differently from regular Spectre is that the device evaluations are run multi-threaded. This encompasses a little overhead, so normally this is switched on when there are at least 256 devices per thread. Also the devices have to require evaluation - in generally this concerns mainly semiconductor models (BSIM, PSP, etc.).

If you do not want to compromise accuracy, there is generally very little you can do in Spectre +turbo. You could try to run with errpreset=liberal, but that reduces accuracy a little - it might be acceptable for your design/simulation.

Another alternative is to consider Virtuoso APS which is a true parallel simulator from Cadence, or look to high performance simulators from other vendors such as AFS from BDA or FineSim from Magma, to name just a few.

Cheers,
Marq

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Geoffrey_Coram Senior Fellow Offline Posts: 1999 Massachusetts, USA	Re: Spectre +turbo Simulations slower than Spectre Simulations Reply #2 - May 27^th, 2010, 5:54am spectre +turbo shouldn't be slower -- Cadence R&D might be interested in your test case. Have you tried other test cases? Can you break off blocks of this netlist and see if you can narrow down where the problem is?
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ywguo

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Re: Spectre +turbo Simulations slower than Spectre Simulations
Reply #3 - May 27^th, 2010, 8:37am

Hi Marq,

This is interesting. I want to know what Spectre + Turbo do in the simulation. Does it run the device evaluation multi-threaded only? I think the device evaluation is done at the begining of a DC/AC/tran analysis. So it cannot reduce the simulation time significantly. Is it correct?

Yawei

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Geoffrey_Coram

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Re: Spectre +turbo Simulations slower than Spectre Simulations
Reply #4 - May 28^th, 2010, 7:08am

ywguo wrote on May 27^th, 2010, 8:37am:

I think the device evaluation is done at the begining of a DC/AC/tran analysis. So it cannot reduce the simulation time significantly. Is it correct?

Yawei - you're confused. �Device evaluation is done for every iteration of every dc sweep point or time point, so speeding up evaluation would certainly speed up dc/tran analysis.

(It might not be a big deal for an ac analysis, since the results for one dc op pt are used for all the frequency points of the sweep, and speeding up evaluation only helps with the dc op pt.)

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If at first you do succeed, STOP, raise your standards, and stop wasting your time.

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ywguo Community Fellow Offline Posts: 943 Shanghai, PRC	Re: Spectre +turbo Simulations slower than Spectre Simulations Reply #5 - May 31^st, 2010, 12:27am Thank you, Geoffrey_Coram.
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