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Date: Wed, 29 Mar 2017 23:12:00 +0200 From: Frederic Weisbecker <fweisbec@...il.com> To: Luiz Capitulino <lcapitulino@...hat.com> Cc: Rik van Riel <riel@...hat.com>, linux-kernel@...r.kernel.org, linux-rt-users@...r.kernel.org, Wanpeng Li <kernellwp@...il.com> Subject: Re: [BUG nohz]: wrong user and system time accounting 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.
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