Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754328AbdC2VMv (ORCPT ); Wed, 29 Mar 2017 17:12:51 -0400 Received: from mail-lf0-f67.google.com ([209.85.215.67]:34276 "EHLO mail-lf0-f67.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753621AbdC2VME (ORCPT ); Wed, 29 Mar 2017 17:12:04 -0400 Date: Wed, 29 Mar 2017 23:12:00 +0200 From: Frederic Weisbecker To: Luiz Capitulino Cc: Rik van Riel , linux-kernel@vger.kernel.org, linux-rt-users@vger.kernel.org, Wanpeng Li Subject: Re: [BUG nohz]: wrong user and system time accounting Message-ID: <20170329211159.GA23895@lerouge> References: <20170323165512.60945ac6@redhat.com> <20170329130447.GB8306@lerouge> <1490793272.28917.5.camel@redhat.com> <20170329092357.2ca784c2@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20170329092357.2ca784c2@redhat.com> User-Agent: Mutt/1.5.24 (2015-08-30) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1589 Lines: 70 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 > #include > #include > #include > #include > > 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.