Re: Raspberry Pi 3 & 3+ speed issues

[John Klos <john%klos.com@localhost>]

> > So they're basically both running at the same speed. At 600 MHz, they both
> > take about 24.5 seconds to count the first million prime numbers, meaning
> > that the Pi 3+, which says it's running at 1400 MHz, is really running at
> > 1200 MHz.
>
> Maybe another test shows a difference. If that 'primes' program is
> a common sieve, it will be limited by memory speed, and that is the
> same for pi3 and pi3+.

It counts primes in cache on most CPUs, so I use it to gauge clock speeds, 
even "turbo burst" speeds, by comparing it with results from known clock 
speeds. It's good to ask, and I should've mentioned the kind of counting, 
but even if it were memory bound, the count running at 600 MHz wouldn't be 
exactly half the speed of it running at 1200 MHz :) [1]

dry2 of 10000000 runs:

Microseconds for one run through Dhrystone:    0.3
Dhrystones per Second:                      3436426.0

Microseconds for one run through Dhrystone:    0.3
Dhrystones per Second:                      3424657.5

That's the same, too.

Does anyone out there with a Raspberry Pi 3+ want to check their results 
at (supposedly) 1400 MHz?

John


[1]:

/* Find the nth prime.
   John Klos, john%klos.com@localhost */
#include <stdio.h>
long a=1000000, b=4, c=7, d, e, f=4, g=4, h=4, i=9;
int main() {
 while (b<a) {
  c+=f;
  d=1;
  f=6-f;
  g=4;
  if(e<c) {
   h++;
   e+=i;
   i+=2;
  }
  if(e==c)
    d=c;
  while (d<h) {
   d+=g;
   g=6-g;
   if (!(c%d))
    d=c;
   }
   if (c!=d)
    b+=1;
 }
 printf("%ld, %ld\n",b,c);
}