Re: [9fans] interesting timing tests

[erik quanstrom <quanstro@quanstro.net>]

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oops.  botched fix of harmess warning.
corrected source attached.

just for a giggle, i ran this test on a few handy machines to get a feel
for relative speed of a single core.  since this test is small enough to
fit in the tiniest cache, i would think that memory speed or any other
external factor would be unimportant:

open rd/marvell kirkwood				471.97u 0.00s 472.25r
Intel(R) Atom(TM) CPU  330   @ 1.60GHz		48.47u 0.00s 48.48r
Intel(R) Pentium(R) 4 CPU 3.00GHz		40.72u 0.00s 40.76r
AMD Athlon(tm) 64 X2 Dual Core Processor 3800+	30.62u 0.00s 30.64r
AMD Athlon(tm) 64 X2 Dual Core Processor 5000+	23.18u 0.00s 23.19r
Intel(R) Xeon(R) CPU            5120  @ 1.86GHz	23.16u 0.00s 23.08r
Intel(R) Xeon(R) CPU           E5540  @ 2.53GHz	17.26u 0.00s 17.26r
Intel(R) Core(TM) i7 CPU         920  @ 2.67GHz	16.86u 0.00s 16.86r
Intel(R) Xeon(R) CPU           E5630  @ 2.53GHz	10.46u 0.00s 10.50r

perhaps the arm's vlong arithmitic isn't as well optimized as x86.  the
atom also is conspicuously slow, but unfortunately with no obvious
excuses.

- erik

[-- Attachment #2: burncycles.c --]
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#include <u.h>
#include <libc.h>
#include <thread.h>

#define Scale	(100000000000ull)

/*
 * waste time
 */
vlong
πjj(uint j)
{
	vlong v;

	v = 4*Scale / (2*j + 1);
	if(j&1)
		return -v;
	return v;
}

vlong
π(void)
{
	uint i;
	vlong v;

	v = 0;
	for(i = 0; i < 500000000; i++)
		v += πjj(i);
	return v;
}

void
p(void *v)
{
	int i;

	i = (int)v;
	print("%d: %lld\n", i, π());
	threadexits("");
}

void
usage(void)
{
	fprint(2, "usage: burncycles nthread\n");
	threadexits("usage");
}

void
threadmain(int argc, char **argv)
{
	int n, i;

	ARGBEGIN{
	default:
		usage();
	}ARGEND
	n = 0;
	if(argc == 0)
		n = 1;
	else if(argc != 1 || (n = atoi(argv[0])) <= 0)
		usage();
	for(i = 0; i < n-1; i++)
		proccreate(p, (void*)i, 4096);
	p((void*)i);
}