Pi Only Uses 25% of CPU

[rpiswag]

When I calculate pi or any other cpu intensive task the pi 2's 4 core cpu only ever uses 25%. How can I calculate pi (pi 10000) to use all 4 cores at 100%.

[pluggy]

Welcome to the vague world of multi core CPUs.

Getting 'em to run all 4 doing normal stuff is tricky. Its not difficult to load up all 4 cores for the sake of doing it at the command line, but doing it with real world useful work is something else. If you've got a quad core Windows PC, you'll rarely see it using more than 2, its the same with the Pi.

If you want to see it running at 100%, go into the command line
and do

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yes > /dev/null &

4 times

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killall yes

will stop them all.

[rpiswag]

How can I calculate pi in the command line using all 4 cores?

[Heater]

rpiswag,

Sounds like you need the parallel Chudnovsky algorithm for the Pi:
https://github.com/davidcarver/Parallel-Chudnovsky-PI

This is the algorithm used to gain the world record for calculating digits of Pi. All 10 billion of them!

[rpiswag]

How do I download that pi calculating software in terminal?

[kusti8]

How do I download that pi calculating software in terminal?

Google how to use git. The basic format is:

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git clone url

[DougieLawson]

How do I download that pi calculating software in terminal?

Try this C program

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#include <stdio.h>
int a=10000,b,c=2800,d,e,f[2801],g;
main() {
      for(;b-c;) f[b++] = a/5;
            for( ; d=0,g=c*2; c-=14,printf( "%.4d", e+d/a ), e=d%a )
               for( b=c; d+=f[b]*a, f[b]=d%--g, d/=g--,--b; d*=b);
}

it's left as an exercise for you to work out how that mess gets the results.

[Heater]

I don't know if raspbian has git installed out of the box but if not just do:

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$ sudo apt-get install git

Now clone a copy of the programs source code:

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$ git clone https://github.com/davidcarver/Parallel-Chudnovsky-PI.git

Now compile the program and run it:

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$ cd Parallel-Chudnovsky-PI
$ gcc -fopenmp -Wall -O2 -o raspberry-pi2-openmp raspberry-pi2-openmp.c -lgmp -lm
$ ./raspberry-pi2-openmp 10000 1 2