Re: [BUG nohz]: wrong user and system time accounting

Frederic Weisbecker
2017-03-29T21:12:51Z

On Wed, Mar 29, 2017 at 09:23:57AM -0400, Luiz Capitulino wrote:
>
> There are various reproducers actually. I started off with the simple
> loop above, then wrote the attach program and then wrote the one
> you're mentioning:
>
> http://people.redhat.com/~lcapitul/real-time/acct-bug.c
>
> All of them reproduce the issue 100% of the time for me.

> #define _GNU_SOURCE
> #include <stdio.h>
> #include <unistd.h>
> #include <stdlib.h>
> #include <sched.h>
> #include <sys/types.h>
>
> static int move_to_cpu(int cpu)
> {
> cpu_set_t set;
>
> CPU_ZERO(&set);
> CPU_SET(cpu, &set);
> return sched_setaffinity(0, sizeof(set), &set);
> }
>
> static void loop(void)
> {
> for (;;) ;
> }
>
> static int fork_hog(int cpu)
> {
> int pid;
>
> pid = (int) fork();
> if (pid == 0) {
> move_to_cpu(cpu);
> loop();
> exit(0);
> }
>
> return pid;
> }
>
> int main(int argc, char *argv[])
> {
> int i, pid, cpu, nr_procs;
>
> if (argc != 3) {
> printf("usage: hog < nr-procs > < CPU >\n");
> exit(1);
> }
>
> cpu = atoi(argv[2]);
> nr_procs = atoi(argv[1]);
>
> for (i = 0; i < nr_procs; i++) {
> pid = fork_hog(cpu);
> fprintf(stderr, "created hog%d pid=%d\n", i, pid);
> }
>
> fprintf(stderr, "pausing...\n");
> pause();
>
> return 0;
> }

I just tried both of these and none seem to show incorrect cputime :-/
I'm wondering if that bug depends on some hardware.