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I was using Cuba library to do some integration, but I found that it's generally much slower with parallelization than without.

MWE:

Install["/path/to/Cuba/Vegas"];
SetOptions[Vegas,Verbose->0];
Vegas[Sin[x],{x,0,1},PrecisionGoal->6,MaxPoints->10^6]//AbsoluteTiming
(*{8.48996, {{0.4597, 0.0000217312, 4.32426*10^-14 }}}*)
MapSample = ParallelMap;
Vegas[Sin[x],{x,0,1},PrecisionGoal->6,MaxPoints->10^6]//AbsoluteTiming
(*{55.2991, {{0.4597, 0.0000217312, 4.32426*10^-14 }}}*)

We can see that parallelization (with 16 kernels) is 7 times slower than without parallelization. If I increase the number of kernels to 32, the speed is even slower (102s).

EDIT:

The tests performed above is on a workstation with E5-2680 v3 (48 threads) and I tried both MMA 11.3 and 12.1. I also tested it on a PC with a i7-4790 (only opened 6 kernels) and the MMA version is 12.1. Cuba in question is Cuba-4.2.

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  • $\begingroup$ It would be helpful to know the specs of the rest of the system...often the bottleneck is something else. $\endgroup$
    – DrMrstheMonarch
    Aug 31, 2020 at 11:35
  • $\begingroup$ @morbo I added some infos. Hope it helps. $\endgroup$
    – Turgon
    Sep 1, 2020 at 7:20
  • $\begingroup$ My guess that the MKL is multi-threaded, but ParallelMap sets the maximum number of threads to 1 (one), and you lose the efficiency of the MKL, if the Cuba package is written to take advantage of it. The advice here and in the comments here may be helpful. $\endgroup$
    – Michael E2
    Sep 1, 2020 at 16:25
  • $\begingroup$ @MichaelE2 Manually setting MKLThreadNumber to 4 in parallel kernels didn't help. $\endgroup$
    – Turgon
    Sep 2, 2020 at 19:50

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