Re: Cpu performance with higher order Multipole order

From: Tiago Castro <tiagobscastro_at_gmail.com>
Date: Fri, 11 Dec 2020 20:12:07 +0100

Hi Volker,

  Wow, it represents a substantial improvement to use higher orders then,
fantastic!!

Many thanks!
Cheers,
*Tiago Castro* Post Doc, Department of Physics / UNITS / OATS
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Em sex., 11 de dez. de 2020 às 18:52, Volker Springel <
vspringel_at_mpa-garching.mpg.de> escreveu:

>
> Hi Tiago,
>
> This is the expected behaviour in many situations when you use the
> relative tree opening criterion - in this case, the code tries to maintain
> the same force accuracy independent of the chosen expansion order. Then it
> can happen that higher order is benefecial in the sense that you need less
> CPU time (and fewer tree openings) to reach the same force accuracy.
>
> If you instead set TypeOfOpeningCriterion=0, then the opening angle will
> stay fixed, and selecting higher order will always be slower because you
> are then bound to do more computations (which however increase the force
> accuracy).
>
> Regards,
> Volker
>
>
>
> > On 11. Dec 2020, at 18:17, Tiago Castro <tiagobscastro_at_gmail.com> wrote:
> >
> > Dear List,
> >
> > I have run a series of control runs varying the multipole order on
> Gadget-4. Surprisingly to me, the CPU time significantly reduces with high
> orders. For MULTIPOLE_ORDER = 2, 3, 4 I have a total CPU time of 22466.12,
> 14660.34, 12007.28 respectively. The better performance was due to a
> significant reduction of the time spent in the tree (see the tables below).
> Shouldn't one expect the computational cost to increase with high order
> multipoles? I once again appreciate any clarification on this matter.
> >
> > MO2:
> > Step 2367, Time: 1, CPUs: 156, HighestActiveTimeBin: 20
> > diff cumulative
> > total 78.52 100.0% 22466.12 100.0%
> > treegrav 39.11 49.8% 18540.34 82.5%
> > treebuild 10.05 12.8% 1321.58 5.9%
> > insert 8.90 11.3% 1145.55 5.1%
> > branches 0.18 0.2% 22.01 0.1%
> > toplevel 0.14 0.2% 33.58 0.1%
> > treeforce 29.00 36.9% 17187.79 76.5%
> > treewalk 24.09 30.7% 13786.33 61.4%
> > treeimbalance 4.60 5.9% 3196.94 14.2%
> > treefetch 0.22 0.3% 115.40 0.5%
> > treestack 0.09 0.1% 89.12 0.4%
> > MO3:
> > Step 2399, Time: 1, CPUs: 156, HighestActiveTimeBin: 20
> > diff cumulative
> > total 72.65 100.0% 14660.34 100.0%
> > treegrav 29.72 40.9% 10729.21 73.2%
> > treebuild 10.63 14.6% 1340.10 9.1%
> > insert 9.23 12.7% 1151.05 7.9%
> > branches 0.20 0.3% 24.94 0.2%
> > toplevel 0.18 0.2% 47.31 0.3%
> > treeforce 19.01 26.2% 9350.97 63.8%
> > treewalk 15.91 21.9% 7611.72 51.9%
> > treeimbalance 2.49 3.4% 1533.54 10.5%
> > treefetch 0.55 0.8% 165.79 1.1%
> > treestack 0.06 0.1% 39.92 0.3%
> > MO4:
> > Step 2415, Time: 1, CPUs: 156, HighestActiveTimeBin: 20
> > diff cumulative
> > total 73.47 100.0% 12007.28 100.0%
> > treegrav 26.37 35.9% 8063.34 67.2%
> > treebuild 10.02 13.6% 1386.34 11.5%
> > insert 8.93 12.2% 1173.43 9.8%
> > branches 0.24 0.3% 31.16 0.3%
> > toplevel 0.20 0.3% 65.76 0.5%
> > treeforce 16.29 22.2% 6631.74 55.2%
> > treewalk 13.57 18.5% 5327.90 44.4%
> > treeimbalance 1.85 2.5% 1014.50 8.4%
> > treefetch 0.79 1.1% 250.43 2.1%
> > treestack 0.08 0.1% 38.91 0.3%
> >
> > Cheers,
> > Tiago Castro Post Doc, Department of Physics / UNITS / OATS
> > Phone: (+39 040 3199 120)
> > Mobile: (+39 388 794 1562)
> > Email: tiagobscastro_at_gmail.com
> > Website: tiagobscastro.com
> > Skype: tiagobscastro
> > Address: Osservatorio Astronomico di Trieste / Villa Bazzoni
> > Via Bazzoni, 2, 34143 Trieste TS
> >
> >
> >
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Received on 2020-12-11 20:12:29

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