LTspice Loafing?

What's the processor?

As a "5th gen" low-power i7 the 5500U stacks up pretty poorly against more modern "7th gen" desktop offerings:

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bitrex
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Xeon E5-1603 v3 2.8 GHz. Whatever that means.

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John Larkin         Highland Technology, Inc 
picosecond timing   precision measurement  
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John Larkin

It runs faster if I hide the waveforms. I can minimize the window in fact, and it pops up when done.

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Rick C
Reply to
rickman

Ah, maybe one of the Facebook specials!

They're available refurb on NewEgg for $38, woah.

Reply to
bitrex

Well, it's a Dell box.

Refurbished?

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John Larkin         Highland Technology, Inc 

lunatic fringe electronics
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John Larkin

Am 09.03.2017 um 22:42 schrieb Lasse Langwadt Christensen:

LTspice 4: Linux, virtual Win7 machine VMware Workstation 12: 42 sec same machine in a Linux window LTspice4 with wine under Linux: 22 sec

Machine is a Dell Precision "portable Workstation" 3.5 years old. "portable" has to be taken with a grain of salt. 240W power supply.

I have no idea which run was on which CPU. The CPUs all run at pretty different speed.

regards, Gerhard

system description:

gerhard@precision:~$ inxi -CDb System: Host: precision Kernel: 4.4.0-62-generic x86_64 (64 bit) Desktop: Cinnamon 2.8.8 Distro: Linux Mint 17.3 Rosa Machine: System: Dell product: Precision M6600 v: 01 Mobo: Dell model: 04YY4M v: A00 Bios: Dell v: A15 date:

09/27/2013 CPU: Quad core Intel Core i7-2820QM (-HT-MCP-) cache: 8192 KB clock speeds: max: 3400 MHz 1: 983 MHz 2: 1281 MHz 3: 1301 MHz 4: 1096 MHz 5: 1564 MHz 6: 1029 MHz 7: 1119 MHz 8: 868 MHz Graphics: Card: NVIDIA GF104GLM [Quadro 4000M] Display Server: X.Org 1.15.1 drivers: nvidia (unloaded: fbdev,vesa,nouveau) Resolution: 1920x1080@60.0hz, 2560x1440@60.0hz GLX Renderer: Quadro 4000M/PCIe/SSE2 GLX Version: 4.5.0 NVIDIA 367.57 Network: Card-1: Intel 82579LM Gigabit Network Connection driver: e1000e Card-2: Intel Centrino Ultimate-N 6300 driver: iwlwifi Drives: HDD Total Size: 1536.3GB (74.0% used) ID-1: /dev/sda model: Samsung_SSD_850 size: 1024.2GB ID-2: /dev/sdb model: SAMSUNG_SSD_830 size: 512.1GB Info: Processes: 268 Uptime: 13:11 Memory: 2589.1/16003.5MB Client: Shell (bash) inxi: 2.2.28
Reply to
Gerhard Hoffmann

Less than 15 sec on an HP flaptop (ZBook G3 i7...) with 12% of one cpu. Slower and busier with a plot updating.

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Grizzly H.
Reply to
mixed nuts

20 seconds on my old laptop. On a linux VM!
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John Devereux
Reply to
John Devereux

What I will say, is that I have a behavioural modelled SMPS in SS that runs to settling in around 7 secs on my i7 Novatech laptop, so despite LTSpice being 3 times faster than any other Windows spice, who cares if its GUI is shit :-)

-- Kevin Aylward

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Reply to
Kevin Aylward

On my Dell, that sim runs about 10% slower if I plot the waveform during the run. I can imagine that PCs with slow graphics could take a bigger hit. Do VMs add graphics overhead?

We once rented a compute farm from Amazon to run a slow sim. It wasn't any faster than our 4-core Dells.

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John Larkin         Highland Technology, Inc 

lunatic fringe electronics
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John Larkin

Am 10.03.2017 um 17:20 schrieb John Larkin:

I suppose they do. There must be a lot of exchanging graphics state when switching tasks and there must be a lot of task switches; when I move the cursor from a win7 window to the Linux table top: that looks harmless, but someone has to decide now which operating system has to react on the next click. And that click could trigger actions is a

3D game or 3D layout in Altium Designer.

I also think that the 2nd 2560*144 pixel monitor attached to my laptop slows things down, somewhat. Waveform was ON in my test.

Spice is well-known for being hard to parallelize. It has been tried over and over again. It is not even really floating-point limited. There has been H-spice on the Cray trying to vectorize it. Do you remember all those Weitek/NS32032 coprocessor boards that were sold as Spice accelerators? No one ever made a breakthrough.

Gerhard

Reply to
Gerhard Hoffmann

Does that mean "pulled off a board & re-balled"?

Reply to
Bill Martin

I'd buy one of those Nvidia boards if it would speed up Spice by, say,

100:1.
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John Larkin         Highland Technology, Inc 
picosecond timing   precision measurement  
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John Larkin

Am 10.03.2017 um 17:20 schrieb John Larkin:

I suppose they do. There must be a lot of exchanging graphics state when switching tasks and there must be a lot of task switches; when I move the cursor from a win7 window to the Linux table top: that looks harmless, but someone has to decide now which operating system has to react on the next click. And that click could trigger actions is a

3D game or 3D layout in Altium Designer.

I also think that the 2nd 2560*144 pixel monitor attached to my laptop slows things down, somewhat. Waveform was ON in my test.

Not sure where you get your information from. Spice can, and has been paralysed quite effectively. The core function of parallel processing all the elements in a matrix has been around for a long time in physics applications e.g. solving nuclear bomb equations. Those systems you read about that have Petraflop performance at er..ahmm, 10 MWs of power basically do the same sort of calculations that spice does.

Gaussian elimination of a matrix is a classic software problem that can be parallelised pretty easily. All elements in a row, and all rows, can all be multiplied at once. Each reduction of the matrix size does not depend on any other calculation. Many other software algorithms can be very difficult to parallelise like this.

I use Cadence Spectre every day, and using its APS, multicore features speedups are really good.

There is also Mentors FastSpice, purchased as Berkeley Design Systems, that runs 20 Million analog transistor circuits.

-- Kevin Aylward

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Reply to
Kevin Aylward

Now that's some mighty fine information to know. FWIW Larkin's simulation takes ~ 80s when run from a Remote Desktop session and a mapped Samba share on my ancient 32-bit Pentium 4, 4 GB, W2003 server with LTSpice v4.20.

"If it ain't broke don't fix it."

Thank you,

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Don Kuenz KB7RPU
Reply to
Don Kuenz

In your example LTSpice listing, just change your maximum time step from

10 ns to 10 us. That will give you great speed with no detectable loss of detail.
Reply to
John S

Yes. I do find it surprizing, that many don't even *try* to understand the most basic aspects of Spice when running their simulations. Like, read the manual!

Lots of point mean slower simulations, few points means a jaggered graph. Even with essentially zero knowledge of equations solvers, one should surly expect to just know that high accuracy (reltol=1u) will also slow the simulation.

The forgivable one is TRTOL. Many might not understand how to set this parameter.

Setting this option can make a change of speed of around a factor of 3 or so. The Spice3 default is 7. However, in something like a SMPS this value can often result in incorrect results. I default this to 1 in SuperSpice to make sure results are always accurate. For a whole class of circuits though, increasing it up to say 3 or more will be ok, with a significant speedup. Its worth doing a few runs when setting up your design to get an optimum value for it.

-- Kevin Aylward

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Reply to
Kevin Aylward

I deliberately set the time step short to slow down this simple simulation, so it could be timed in seconds.

But for LC oscillators, the default/automatic time step will create considerable frequency error, several per cent typically. What's awful is simulating high-Q circuits accurately in time domain, like crystal oscillators.

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John Larkin         Highland Technology, Inc 

lunatic fringe electronics
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John Larkin

My sim was intended to run slow.

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John Larkin         Highland Technology, Inc 

lunatic fringe electronics
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John Larkin

I have an option in SS to have variable wait states so that if you are using the "change component values on the schematic in real time" feature, the sim don't finish before you can do so :-)

Yes. A real pain. As noted in my other post though, I find most design work can be done with a de-Qed xtal.

However, for accurate, full Q phase noise, at my day job, its the $100k per seat, per year Cadence Periodic Steady State Phase Noise. I usually use the shooting method, rather than the harmonic balance. Often have to include extra resistance in series with caps to get it to converge though.

Phase noise results in Cadence are very impressive. Usually within the 1dB or so error range. Its a complicated calculation. For every point in the cycle, small signal noise is changing due to different instantaneous currents. It handles it all in the wash. Does really well on up conversion of the 1/f noise of devices and resistors.

I don't know of any freebie PSS/PSSN. It requires a totally different calculation engine than spice

-- Kevin Aylward

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Kevin Aylward

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