linux-kernel - reproducer: utime decreasing

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Message-ID: <4B162551.7050303@jp.fujitsu.com>
Date:	Wed, 02 Dec 2009 17:29:05 +0900
From:	Hidetoshi Seto <seto.hidetoshi@...fujitsu.com>
To:	Stanislaw Gruszka <sgruszka@...hat.com>
CC:	Ingo Molnar <mingo@...e.hu>, Thomas Gleixner <tglx@...utronix.de>,
	Peter Zijlstra <peterz@...radead.org>,
	Spencer Candland <spencer@...ehost.com>,
	Américo Wang <xiyou.wangcong@...il.com>,
	linux-kernel@...r.kernel.org, Oleg Nesterov <oleg@...hat.com>,
	Balbir Singh <balbir@...ibm.com>
Subject: reproducer: utime decreasing

Following is a sample program that can reproduce the problem
in several ways.

I tested my patch using this reproducer, and confirmed that
applying both of Stanislaw's do_sys_times() patch and my
thread_group_times() patch is required to fix the problem.


Thanks,
H.Seto

===
/*
 * Sample program to demonstrate time decreasing on thread exit
 */

#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <pthread.h>
#include <sys/times.h>

#define DEFAULT_THREADS 500

unsigned long lpt;
int looptype;
int samplesleep;
int threads;

void *child (void *thread_id)
{
	struct tms t[12];
  	int i, j;
	unsigned long ret = 0, id = (unsigned long)thread_id;

	if (looptype) {
		/*
		 * discont:
		 *
		 *  Loop tricky, to make a significant gap between
		 *  task->{u,s}time and task_times().
		 *
		 *	runtime of a thread  = 0.5 tick * 1000 = 500 ms
		 *	task->{u,s}time	     = (??? , 0)
		 *	task_times()         = ideally (500, 0)
		 */
		for (j = 0; j < 1000; j++) {
			for (i = 0; i < lpt/2; i++)
				;
			usleep(0);
		}
	} else {
		/*
		 * cont:
		 *
		 *  Loop without tricks.
		 *
		 *	runtime of a thread  = 500 ms
		 *	task->{u,s}time      = (500, 0)
		 *	task_times()         = (500, 0)
		 */
		for (i = 0; i < lpt * 500; i++)
			;
	}

	if (!(id % 4))
		/* bother other threads */
		pthread_exit((void *)ret);

	for (i = 0; i < 12; i++) {
		times(&t[i]);
		if (samplesleep)
			usleep(0);
	}

	for (i = 0; i + 5 < 12; i++) {
		/*
		 *  +----+----+----+----+----+
		 * i+0  i+1  i+2  i+3  i+4  i+5
		 *            ^^^^^^
		 *          check here
		 */
		if (t[i+2].tms_utime > t[i+3].tms_utime
		    || t[i+2].tms_stime > t[i+3].tms_stime) {

		   printf("[%4ld] %s decreased %3d: "
			  "(%d %d) (%d %d) [%d %d]<->[%d %d] (%d %d) (%d %d)\n",
				id,
				t[i+2].tms_utime > t[i+3].tms_utime ?
							"utime" : "stime",
				t[i+2].tms_utime > t[i+3].tms_utime ?
				  t[i+3].tms_utime - t[i+2].tms_utime :
				  t[i+3].tms_stime - t[i+2].tms_stime,
				t[i+0].tms_utime, t[i+0].tms_stime,
				t[i+1].tms_utime, t[i+1].tms_stime,
				t[i+2].tms_utime, t[i+2].tms_stime,
				t[i+3].tms_utime, t[i+3].tms_stime,
				t[i+4].tms_utime, t[i+4].tms_stime,
				t[i+5].tms_utime, t[i+5].tms_stime);
		   ret = 1;
		}
	}

	pthread_exit((void *)ret);
}

void get_loops_per_tick(void)
{
	struct tms t1, t2;
	unsigned long i, mloop = 1000 * 1000 * 1000;

	times(&t1);
	for (i = 0; i < mloop; i++)
		;
	times(&t2);

	lpt = mloop / ((t2.tms_utime - t1.tms_utime) * 10);
}

void do_test(int c)
{
	struct tms t1, t2;
	clock_t j1, j2;
	pthread_t *th;
	unsigned long i, ret = 0;

	th = calloc(threads, sizeof(pthread_t));
	if (!th)
		return;

	looptype    = !!(c & 0x1) ? 1 : 0;
	samplesleep = !!(c & 0x2) ? 1 : 0;
	printf("looptype    : %s\n", looptype ? "discont" : "cont");
	printf("samplesleep : %s\n", samplesleep ? "yes" : "no");

	printf(" ## start ##\n");
	j1 = times(&t1);
	for (i = 0; i < threads; i++)
		pthread_create (&th[i], NULL, child, (void *)i);
	for (i = 0; i < threads; i++) {
		int r;
		pthread_join(th[i], (void *)&r);
		ret += (int)r;
	}
	j2 = times(&t2);
	printf(" ## done. ##\n");
	printf(" loop total:\n");
	printf("  user   : %7d ms\n", (t2.tms_utime - t1.tms_utime) * 10);
	printf("  system : %7d ms\n", (t2.tms_stime - t1.tms_stime) * 10);
	printf("  elapse : %7d ms\n", (j2 - j1) * 10);
	printf("  error  : %d\n\n", ret);

	printf("result: %s\n\n", ret ? "BAD" : "GOOD");
}

int main(int argc, char **argv)
{
	int i;

	threads = argc > 1 ? atoi(argv[1]) : DEFAULT_THREADS;

	printf("### Prep:\n");
	get_loops_per_tick();
	printf("loops_per_tick: %ld\n", lpt);
	printf("threads       : %d\n\n", threads);

	printf("### Test:\n");
	for (i = 0; i < 4; i++)
		do_test(i);
}

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