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

[Adhemerval Zanella <adhemerval dot zanella at linaro dot org>]

On 06/02/2020 11:48, Lucas A. M. Magalhaes wrote:
> 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.
> 
> ---
> 
> 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

None of the files follow the code and style guideline [1].

[1] https://sourceware.org/glibc/wiki/Style_and_Conventions

> 
>  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);
> +}

I don't using float operation is the correct solution to handle both
invalid inputs and overflow results. We already have a working solution
(support/timespec-add.c and support/timespec-sub.c), why do you need
to add such functions?

> +
> +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 );
> +}
> +

Please add some description of what this function do.  And I think 
it would be better to normalize to nanoseconds instead of seconds
to avoid floating-point cancellation due the range difference.
Something like:

  /* Return true if the DIFF time is within the ratio 
     [upper_bound, lower_bound] of DIFF time, or false otherwise.

     For instance:

     struct timespec diff = { 3, 94956 };
     struct timespec base = { 4, 0 };

     The call checks if the ratio of diff/base is within the
     bounds of (0.65, 1.0) (i.e, if 'diff' is at least 65% of
     the 'base' value).

     support_timespec_check_in_range (base, diff, 1.0, 0.65); */
  bool support_timespec_check_ratio (struct timespec base,
                                     struct timespec diff,
                                     double upper_bound,
                                     double lower_bound)
  {
    assert (upper_bound >= lower_bound);
    uint64_t base_norm = base.tv_sec * TIMESPEC_HZ + base.tv_nsec;
    uint64_t diff_norm = diff.tv_sec * TIMESPEC_HZ + diff.tv_nsec;
    double ratio = (double) base_norm / (double) diff_norm;
    return ratio >= lower_bound && ratio <= upper_bound;
  }
   

I think it should follow the libsupport name convention of prepending
'support_' on file name. 

The same name convention should be used on the exported interfaces
(support_*).

And I see that using time_* is confusing because the underlying type
is a 'timespec'. On 'include/time.h' the type is used on function
name, I think we should do the same here.


> 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 implementation is not based on old tests, I think the copyright
years should be only 2020.

> +   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 */

As before.

> 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;
>