I want to test if for any prime n > 3, that (n+1)(n-1) is not divisible by 24. I want it to execute it on all cores. I have this code, which is virtually the same as one of the examples in the documentation,
https://reference.wolfram.com/language/ref/ParallelEvaluate.html
under "Neat Examples" which checks if n! + 1 is prime.
Whilst Mathematics is launching multiple kernels, the "top" command on linux shows one of them is using about 75% of the CPU time, and the others about 1%. All kernels except one run for 8 to 10 seconds. The top command on this machine is configured such that percentages are based on the individual cores, not the sum of all cores, so the sum of the CPU times should far exceed 100%.
ParallelEvaluate[$RecursionLimit = 500]
n = 1; primes = {}; SetSharedVariable[n, primes];
PrintTemporary[Dynamic[{n, primes}]];
CheckAbort[
ParallelEvaluate[While[True,
With[{n = n++},
If[Mod[(Prime[n] + 1) (Prime[n] - 1), 24] != 0 ,
AppendTo[primes, n]]]]],
{n, primes}]
Here's the output from top. The load average of the computer is 1.55, which is pretty low. A serial version of the code would run faster. Can anyone suggest a better way to do this, which will make more use of multiple cores?
top - 00:02:11 up 9:49, 1 user, load average: 1.55, 1.48, 1.78
Tasks: 717 total, 4 running, 713 sleeping, 0 stopped, 0 zombie
%Cpu(s): 2.7 us, 0.5 sy, 0.0 ni, 96.7 id, 0.0 wa, 0.0 hi, 0.0 si, 0.0 st
MiB Mem : 385596.8 total, 372310.2 free, 8849.1 used, 4437.5 buff/cache
MiB Swap: 2048.0 total, 2048.0 free, 0.0 used. 374307.1 avail Mem
PID USER PR NI VIRT RES SHR S %CPU %MEM TIME+ COMMAND
40619 drkirkby 20 0 5541304 172432 72212 R 66.3 0.0 3:28.18 WolframKernel
15761 drkirkby 20 0 4811860 904880 225976 S 17.9 0.2 21:24.35 firefox
31080 drkirkby 20 0 3942452 261308 132848 S 15.2 0.1 3:16.16 Mathematica
38667 drkirkby 20 0 2552824 228688 107152 S 12.1 0.1 0:51.26 Isolated Web Co
2481 drkirkby 20 0 4573500 450416 127528 S 7.2 0.1 8:38.70 gnome-shell
2129 root 20 0 24.2g 118088 70232 R 3.7 0.0 5:45.92 Xorg
2171 root -51 0 0 0 0 S 2.6 0.0 2:15.89 irq/165-nvidia
2113 drkirkby 9 -11 2908504 20416 15792 S 1.4 0.0 8:05.07 pulseaudio
41350 drkirkby 20 0 1082404 136948 58796 S 1.0 0.0 0:04.14 WolframKernel
40686 drkirkby 20 0 1082404 136548 58396 S 0.9 0.0 0:04.38 WolframKernel
40687 drkirkby 20 0 1307832 159464 65268 S 0.9 0.0 0:06.14 WolframKernel
40709 drkirkby 20 0 1082400 136612 58460 S 0.9 0.0 0:04.24 WolframKernel
