Re: [PATCH v2] Fix time/tst-cpuclock1 intermitent failures

["Lucas A. M. Magalhaes" <lamm@linux.ibm.com>]

Quoting Lucas A. M. Magalhaes (2020-02-06 11:48:19)
> This test fails intermittently in systems with heavy load as
> CLOCK_PROCESS_CPUTIME_ID is subject to scheduler pressure.  Thus the
> test boundaries where relaxed to keep it from fail on this systems.
> 
> A refactor of the spent time checking was made with some support
> functions. With the advantage to represent time jitter in percent
> of the target.
> 
> The values used by the test boundaries are all empirical.
> 
> ---

Ping.

> 
> Hi,
> 
> Please Carlos see if this is what you asked.
> 
> I spent sometime gathering the spent times to find the values
> for the boundaries. From this I selected values that will fail less
> than 1% of the time, in the tested machines.
> 
> Also as I found the spent time deviation completely asymmetrical
> I choose to separate the values in upper and lower bounds.
> 
> changes from V2:
>         - Add support functions
> 
>  support/Makefile     |  1 +
>  support/cpuclock.c   | 51 ++++++++++++++++++++++++++++++++++++++++++++
>  support/cpuclock.h   | 30 ++++++++++++++++++++++++++
>  time/tst-cpuclock1.c | 43 ++++++++++---------------------------
>  4 files changed, 93 insertions(+), 32 deletions(-)
>  create mode 100644 support/cpuclock.c
>  create mode 100644 support/cpuclock.h
> 
> diff --git a/support/Makefile b/support/Makefile
> index 3325feb790..b308fe0856 100644
> --- a/support/Makefile
> +++ b/support/Makefile
> @@ -31,6 +31,7 @@ libsupport-routines = \
>    check_dns_packet \
>    check_hostent \
>    check_netent \
> +  cpuclock \
>    delayed_exit \
>    ignore_stderr \
>    next_to_fault \
> diff --git a/support/cpuclock.c b/support/cpuclock.c
> new file mode 100644
> index 0000000000..f40c7e8d4a
> --- /dev/null
> +++ b/support/cpuclock.c
> @@ -0,0 +1,51 @@
> +/* Support functions for cpuclock tests.
> +   Copyright (C) 2018-2020 Free Software Foundation, Inc.
> +   This file is part of the GNU C Library.
> +
> +   The GNU C Library is free software; you can redistribute it and/or
> +   modify it under the terms of the GNU Lesser General Public
> +   License as published by the Free Software Foundation; either
> +   version 2.1 of the License, or (at your option) any later version.
> +
> +   The GNU C Library is distributed in the hope that it will be useful,
> +   but WITHOUT ANY WARRANTY; without even the implied warranty of
> +   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
> +   Lesser General Public License for more details.
> +
> +   You should have received a copy of the GNU Lesser General Public
> +   License along with the GNU C Library; if not, see
> +   <https://www.gnu.org/licenses/>.  */
> +
> +#include "cpuclock.h"
> +#include <stdlib.h>
> +
> +#define T_1s 1000000000.0
> +
> +struct timespec time_normalize(struct timespec t) {
> +       int diff;
> +       diff = (t.tv_nsec / T_1s);
> +       t.tv_sec += diff;
> +       t.tv_nsec += -(diff * T_1s);
> +       return t;
> +}
> +
> +struct timespec time_add(struct timespec a, struct timespec b) {
> +       struct timespec s = {.tv_sec = a.tv_sec + b.tv_sec,
> +                            .tv_nsec = a.tv_nsec + b.tv_nsec};
> +       return time_normalize(s);
> +}
> +
> +struct timespec time_sub(struct timespec a, struct timespec b) {
> +       struct timespec d = {.tv_sec = a.tv_sec - b.tv_sec,
> +                            .tv_nsec = a.tv_nsec - b.tv_nsec};
> +       return time_normalize(d);
> +}
> +
> +int percent_diff_check(struct timespec base, struct timespec dev,
> +                      float upper_bound, float lower_bound) {
> +       double timea = base.tv_sec + base.tv_nsec / T_1s;
> +       double timeb = dev.tv_sec + dev.tv_nsec / T_1s;
> +       double diff = (timea - timeb) / (0.5 * (timea + timeb));
> +       return (diff >= -upper_bound && diff <= lower_bound );
> +}
> +
> diff --git a/support/cpuclock.h b/support/cpuclock.h
> new file mode 100644
> index 0000000000..2505fbdcff
> --- /dev/null
> +++ b/support/cpuclock.h
> @@ -0,0 +1,30 @@
> +/* Support functions for cpuclock tests.
> +   Copyright (C) 2018-2020 Free Software Foundation, Inc.
> +   This file is part of the GNU C Library.
> +
> +   The GNU C Library is free software; you can redistribute it and/or
> +   modify it under the terms of the GNU Lesser General Public
> +   License as published by the Free Software Foundation; either
> +   version 2.1 of the License, or (at your option) any later version.
> +
> +   The GNU C Library is distributed in the hope that it will be useful,
> +   but WITHOUT ANY WARRANTY; without even the implied warranty of
> +   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
> +   Lesser General Public License for more details.
> +
> +   You should have received a copy of the GNU Lesser General Public
> +   License along with the GNU C Library; if not, see
> +   <https://www.gnu.org/licenses/>.  */
> +
> +#ifndef SUPPORT_CPUCLOCK_H
> +#define SUPPORT_CPUCLOCK_H
> +
> +#include <time.h>
> +
> +struct timespec time_normalize(struct timespec t);
> +struct timespec time_add(struct timespec a, struct timespec b);
> +struct timespec time_sub(struct timespec a, struct timespec b);
> +int percent_diff_check(struct timespec base, struct timespec dev,
> +                      float upper_bound, float lower_bound);
> +
> +#endif /* SUPPORT_CPUCLOCK_H */
> diff --git a/time/tst-cpuclock1.c b/time/tst-cpuclock1.c
> index 0120906f23..4051de1646 100644
> --- a/time/tst-cpuclock1.c
> +++ b/time/tst-cpuclock1.c
> @@ -26,6 +26,7 @@
>  #include <signal.h>
>  #include <stdint.h>
>  #include <sys/wait.h>
> +#include <support/cpuclock.h>
>  
>  /* This function is intended to rack up both user and system time.  */
>  static void
> @@ -155,19 +156,11 @@ do_test (void)
>    printf ("live PID %d after sleep => %ju.%.9ju\n",
>           child, (uintmax_t) after.tv_sec, (uintmax_t) after.tv_nsec);
>  
> -  struct timespec diff = { .tv_sec = after.tv_sec - before.tv_sec,
> -                          .tv_nsec = after.tv_nsec - before.tv_nsec };
> -  if (diff.tv_nsec < 0)
> -    {
> -      --diff.tv_sec;
> -      diff.tv_nsec += 1000000000;
> -    }
> -  if (diff.tv_sec != 0
> -      || diff.tv_nsec > 600000000
> -      || diff.tv_nsec < 100000000)
> +  struct timespec diff = time_sub(after, before);
> +  if (!percent_diff_check(sleeptime, diff, .3, 2))
>      {
>        printf ("before - after %ju.%.9ju outside reasonable range\n",
> -             (uintmax_t) diff.tv_sec, (uintmax_t) diff.tv_nsec);
> +           (uintmax_t) diff.tv_sec, (uintmax_t) diff.tv_nsec);
>        result = 1;
>      }
>  
> @@ -194,19 +187,11 @@ do_test (void)
>         }
>        else
>         {
> -         struct timespec d = { .tv_sec = afterns.tv_sec - after.tv_sec,
> -                               .tv_nsec = afterns.tv_nsec - after.tv_nsec };
> -         if (d.tv_nsec < 0)
> -           {
> -             --d.tv_sec;
> -             d.tv_nsec += 1000000000;
> -           }
> -         if (d.tv_sec > 0
> -             || d.tv_nsec < sleeptime.tv_nsec
> -             || d.tv_nsec > sleeptime.tv_nsec * 2)
> +         diff = time_sub(afterns, after);
> +         if (!percent_diff_check(sleeptime, diff, .6, .34))
>             {
>               printf ("nanosleep time %ju.%.9ju outside reasonable range\n",
> -                     (uintmax_t) d.tv_sec, (uintmax_t) d.tv_nsec);
> +                    (uintmax_t) diff.tv_sec, (uintmax_t) diff.tv_nsec);
>               result = 1;
>             }
>         }
> @@ -241,20 +226,14 @@ do_test (void)
>    printf ("dead PID %d => %ju.%.9ju\n",
>           child, (uintmax_t) dead.tv_sec, (uintmax_t) dead.tv_nsec);
>  
> -  diff.tv_sec = dead.tv_sec - after.tv_sec;
> -  diff.tv_nsec = dead.tv_nsec - after.tv_nsec;
> -  if (diff.tv_nsec < 0)
> -    {
> -      --diff.tv_sec;
> -      diff.tv_nsec += 1000000000;
> -    }
> -  if (diff.tv_sec != 0 || diff.tv_nsec > 200000000)
> +  diff = time_sub(dead, after);
> +  sleeptime.tv_nsec = 100000000;
> +  if (!percent_diff_check(sleeptime, diff, .6, .36))
>      {
>        printf ("dead - after %ju.%.9ju outside reasonable range\n",
> -             (uintmax_t) diff.tv_sec, (uintmax_t) diff.tv_nsec);
> +            (uintmax_t) diff.tv_sec, (uintmax_t) diff.tv_nsec);
>        result = 1;
>      }
> -
>    /* Now reap the child and verify that its clock is no longer valid.  */
>    {
>      int x;
> -- 
> 2.20.1
>