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Subject: RE: [PATCH] sched: Folding nohz load accounting more accurate
From: Peter Zijlstra <peterz@infradead.org>
To: Doug Smythies <dsmythies@telus.net>
Cc: "'Charles Wang'" <muming.wq@gmail.com>, linux-kernel@vger.kernel.org,
        "'Ingo Molnar'" <mingo@redhat.com>,
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Date: Mon, 18 Jun 2012 12:13:15 +0200
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On Wed, 2012-06-13 at 20:13 -0700, Doug Smythies wrote:
> ./waiter 2 900 345912 9444

So we're all simply just trying to burn a particular amount of cpu-time?

I have a little consume.c thing lying about doing something like that.
Its independent of clockspeed, but doesn't really like preemption much,
but it more or less works ;-)

---
#include <sys/time.h>
#include <unistd.h>
#include <stdio.h>

unsigned long long stamp(void)
{
	struct timeval tv;

	gettimeofday(&tv, NULL);

	return (unsigned long long)tv.tv_sec * 1000000 + tv.tv_usec;
}

void consume(int spin, int total)
{
	unsigned long long begin, now;

	begin = stamp();

	for (;;) {
		now = stamp();
		if ((long long)(now - begin) > spin) {
			usleep(total - spin);
			begin += total;
		}
	}
}

int main(int argc, char **argv)
{
	int period = 100000; /* 100ms */
	int frac;

	if (argc < 2) {
		fprintf(stderr, "%s <frac> [<period>]\n"
				"  frac   -- [1-100] %% of time to burn\n"
				"  period -- [usec] period of burn/sleep cycle\n",
				argv[0]);
		return -1;
	}

	frac = atoi(argv[1]);
	if (argc > 2)
		period = atoi(argv[2]);

	if (frac > 100)
		frac = 100;

	if (frac < 1)
		frac = 1;

	consume((period * frac) / 100, period);

	return 0;
}

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