Cpu performance with higher order Multipole order

From: Tiago Castro <tiagobscastro_at_gmail.com>
Date: Fri, 11 Dec 2020 18:17:10 +0100

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
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Received on 2020-12-11 18:17:34

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