How much processing power a computer has [closed] - c

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I have this following code, which I run in the terminal.
In another terminal i have 'top' open, where i am able to see the %CPU of the new process i create. I run this for the number of processes (N); 2, 4, 8, 16.
The average %CPU from each i report back is..
2 - 100%
4 - 97%
8 - 50%
16 - 25%
How can the processing power of the computer be determined by these results?
#include <stdio.h>
#include <stdlib.h>
#include <math.h>
#define N 2 /* define the total number of processes we want */
/* Set global variable */
float total=0;
/* compute function just does something. */
int compute()
{
int i;
float oldtotal=0, result=0;
/* for a large number of times just square root and square
the arbitrary number 1000 */
for(i=0;i<2000000000;i++)
{
result=sqrt(1000.0)*sqrt(1000.0);
}
/* Print the result – should be no surprise */
printf("Result is %f\n",result);
/* We want to keep a running total in the global variable total */
oldtotal = total;
total = oldtotal + result;
/* Print running total so far. */
printf("Total is %f\n",total);
return(0);
}
int main()
{
int pid[N], i, j;
float result=0;
printf("\n"); /* bit of whitespace */
/* We want to loop to create the required number of processes
Note carefully how only the child process is left to run */
for(i=0;i<N;i++)
{
/* Do the fork and catch it if it/one fails */
if((pid[i]=fork())==-1)
{
exit(1);
}
/* now with child we want to do our computation */
else if(pid[i] > 0)
{
/* give a message about the proc ID */
printf("Process Id for process %d is %d\n",i,getpid());
/* call the function to do some computation. If we used sleep
The process would simply sleep. We do not want that */
compute();
/* After we have done our computation we must quit the for
loop otherwise we get a fork bomb! */
break;
}
}
/* nothing else to do so end main function (and program) */
return 0;
}

Answer 1

It depends on your definition of processing power. The classic way is number of instructions per second (MIPS) or floating point operations per second (FLOPs).
Finding MIPS is fiddly because in C code you don't know how many instructions each line of code represents.
You can do a mega-flops calculation though. Loop in C doing a float * float operation of random numbers. See how long it takes to do a lot of calculations (say 109) then calculate how many you did in a second.
Then multiply by the number of processors you have.

Answer 2

Your results show very less difference between the CPU usages for 2 processes and 4 processes so it is almost certainly a quad core processor. Apart from that, not much can be told about the about the speed of the processor with just the percentages. You have also used printf statements which make it even harder to calculate the processing speed since they occasionally flush the buffer.

Answer 3

"Processing power" is a suggestive, yet annoyingly vague term. For most purposes, we don't care about MIPs or FIPs—only for pure number crunching do we give it any mind. Even then, it is as useless a measure for comparing computers as it is to compare automobiles with their maximum RPMs. See BogoMips.
Even with MIPs and FIPs, usually peak performance is measured. Many don't try to determine average values.
Another useful parameter of CPU power is branches per second—which no one measures (but they should). BPS varies considerably based on the intricacies of the CPU architecture, caching, paging, perhaps context switching, and the nature of the branches.
In any useful program, input and output is part of computing power. Hence bandwidth of memory, i/o devices, file systems, and connecting devices, networks, etc. are part of the computer's "computing power".
If you mean a subset of these, please clarify your question.