[v7] Fix time/tst-cpuclock1 intermitent failures

  This test fails intermittently in systems with heavy load as
CLOCK_PROCESS_CPUTIME_ID is subject to scheduler pressure.  Thus the
test boundaries were relaxed to keep it from failing on such systems.

A refactor of the spent time checking was made with some support
functions.  With the advantage to representing time jitter in percent
of the target.

The values used by the test boundaries are all empirical.

---

Hi,

changes on V7:
	- change expecting boundaries
	- add comments

changes on V6:
	- add overflow handling
	- change variables names

changes on V5:
	- add tests for support_timespec_check_in_range
	- fix support_timespec_normalize
	- add comments
	- fix style

changes on V4:
	- move functions to support/timespec.c
	- simplify functions

changes on V3:
	- refactor support functions
	- use existing timespec-sub function

changes on V2:
	- Add support functions
---
 support/Makefile       |   1 +
 support/timespec.c     |  55 +++++++++++++++
 support/timespec.h     |   6 ++
 support/tst-timespec.c | 147 +++++++++++++++++++++++++++++++++++++++++
 time/tst-cpuclock1.c   |  48 +++++---------
 5 files changed, 227 insertions(+), 30 deletions(-)
 create mode 100644 support/tst-timespec.c
  

On 4/3/20 3:24 PM, 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 were relaxed to keep it from failing on such systems.
> 
> A refactor of the spent time checking was made with some support
> functions.  With the advantage to representing time jitter in percent
> of the target.
> 
> The values used by the test boundaries are all empirical.
> 

Looking forward to v8. I think we're almost done. If you fixup the
TIMESPEC_SHRINK interface (static inline API moved to support with
a few testes) then it's good to checkin next time.

Thank you for your patience!

> ---
> 
> Hi,
> 
> changes on V7:
> 	- change expecting boundaries
> 	- add comments
> 
> changes on V6:
> 	- add overflow handling
> 	- change variables names
> 
> changes on V5:
> 	- add tests for support_timespec_check_in_range
> 	- fix support_timespec_normalize
> 	- add comments
> 	- fix style
> 
> changes on V4:
> 	- move functions to support/timespec.c
> 	- simplify functions
> 
> changes on V3:
> 	- refactor support functions
> 	- use existing timespec-sub function
> 
> changes on V2:
> 	- Add support functions
> ---
>  support/Makefile       |   1 +
>  support/timespec.c     |  55 +++++++++++++++
>  support/timespec.h     |   6 ++
>  support/tst-timespec.c | 147 +++++++++++++++++++++++++++++++++++++++++
>  time/tst-cpuclock1.c   |  48 +++++---------
>  5 files changed, 227 insertions(+), 30 deletions(-)
>  create mode 100644 support/tst-timespec.c
> 
> diff --git a/support/Makefile b/support/Makefile
> index 6e38b87ebe..cacaac96a5 100644
> --- a/support/Makefile
> +++ b/support/Makefile
> @@ -233,6 +233,7 @@ tests = \
>    tst-test_compare \
>    tst-test_compare_blob \
>    tst-test_compare_string \
> +  tst-timespec \

OK.

>    tst-xreadlink \
>    tst-xsigstack \
>  
> diff --git a/support/timespec.c b/support/timespec.c
> index ea6b947546..f6b3f87bb1 100644
> --- a/support/timespec.c
> +++ b/support/timespec.c
> @@ -19,6 +19,8 @@
>  #include <support/timespec.h>
>  #include <stdio.h>
>  #include <stdint.h>
> +#include <assert.h>
> +#include <intprops.h>

OK.

>  
>  void
>  test_timespec_before_impl (const char *file, int line,
> @@ -57,3 +59,56 @@ test_timespec_equal_or_after_impl (const char *file, int line,
>  	    (intmax_t) diff.tv_sec, (intmax_t) diff.tv_nsec);
>    }
>  }
> +
> +/* Returns t normalized timespec with .tv_nsec < TIMESPEC_HZ
> +   and the overflows added to .tv_sec. It assumes times are
> +   positive.  */
> +struct timespec
> +support_timespec_normalize (struct timespec time)
> +{
> +  struct timespec norm;
> +  if (INT_ADD_WRAPV (time.tv_sec, (time.tv_nsec / TIMESPEC_HZ), &norm.tv_sec))
> +   {
> +     norm.tv_sec = (time.tv_nsec < 0) ? TYPE_MINIMUM (time_t):TYPE_MAXIMUM (time_t);

OK. Overflow sets max value, while underflow sets min value (will look for those tests).

> +   }
> +  norm.tv_nsec = time.tv_nsec % TIMESPEC_HZ;

OK.

> +  return norm;
> +}
> +

Needs comment:

/* Convert TIME to nanoseconds stored in shrinked.  */

> +#define TIMESPEC_SHRINK(time, shrinked) 				\

(1) The name should indicate what it does.

Shink isn't quite what we're doing here.

We're converting struct timespec to ns.

Plese call this timespec_ns(time), and make it a static inline
that returns the converted long value.

(2) Choose static inlines over macros.

Macros are hard to debug and we get better diagnostics with static inlines,
please prefer them over macros.

(3) Implement pure functions over functions that mutate arguments.

Also from a design perspective it's better to create interfaces that take
const input, produce a value, and return that value in an immutable result.
This way the caller controls the manner in which the store is carried out.
The function is therefore pure and you know it has no side-effects
on the parameters. Pure functions are easier to debug, reason about,
combine, and parallelize :-)

For example:

   expected_norm = timespec_ns (time);

Then you do this:

> +{									\
     long ns;
> +  if (INT_MULTIPLY_WRAPV(time.tv_sec, TIMESPEC_HZ, &shrinked))		\
> +   {									\
> +      shrinked = (time.tv_sec < 0) ? TYPE_MINIMUM(long): TYPE_MAXIMUM(long); \
> +   }									\
> +  if (INT_ADD_WRAPV(shrinked, time.tv_nsec, &shrinked))			\
> +   {									\
> +      shrinked = (time.tv_nsec < 0) ? TYPE_MINIMUM(long): TYPE_MAXIMUM(long); > +   }									\
     /* Return the converted ns value.  */
     return ns;
> +}									\

Can you move this generic routine out of this test now and into support/timespec.h?

This function needs tests to verify the behaviour of the edge cases
(including overflow and underflow). You can put the tests into the
same new test if you like because they are related.

> +
> +/* Returns TRUE if the observed time is within the given percentage bounds of
> +the expected time, and FALSE otherwise.
> +For example the call
> +
> +support_timespec_check_in_range(expected, observed, .5, 1.2);
> +
> +will check if
> +
> +.5 <= observed/expected <= 1.2
> +
> +In other words it will check if observed time is within 50% to 120% of
> +the expected time.  */
> +int
> +support_timespec_check_in_range (struct timespec expected, struct timespec observed,
> +			      double lower_bound, double upper_bound)
> +{
> +  assert (upper_bound >= lower_bound);
> +  long expected_norm, observed_norm;
> +  TIMESPEC_SHRINK(expected, expected_norm);

     expected_norm = timespec_ns (expected);

> +  /* Don't divide by zero  */
> +  assert(expected_norm != 0);
> +  TIMESPEC_SHRINK(observed, observed_norm);

     Likewise.

> +  double ratio = (double)observed_norm / expected_norm;
> +  return (lower_bound <= ratio && ratio <= upper_bound);
> +}
> diff --git a/support/timespec.h b/support/timespec.h
> index c5852dfe75..86040627c2 100644
> --- a/support/timespec.h
> +++ b/support/timespec.h
> @@ -48,6 +48,12 @@ void test_timespec_equal_or_after_impl (const char *file, int line,
>                                          const struct timespec left,
>                                          const struct timespec right);
>  
> +struct timespec support_timespec_normalize (struct timespec time);
> +
> +int support_timespec_check_in_range (struct timespec expected, struct timespec observed,
> +				  double lower_bound, double upper_bound);

OK.

> +
> +
>  /* Check that the timespec on the left represents a time before the
>     time on the right. */
>  #define TEST_TIMESPEC_BEFORE(left, right)                               \
> diff --git a/support/tst-timespec.c b/support/tst-timespec.c
> new file mode 100644
> index 0000000000..06d817a421
> --- /dev/null
> +++ b/support/tst-timespec.c
> @@ -0,0 +1,147 @@
> +/* Test for support_timespec_check_in_range function.

OK.

> +   Copyright (C) 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 <support/timespec.h>
> +#include <support/check.h>
> +#include <limits.h>
> +
> +struct timespec_test_case
> +{
> +  struct timespec expected;
> +  struct timespec observed;
> +  double upper_bound;
> +  double lower_bound;
> +  int result;
> +};
> +
> +struct timespec_test_case test_cases[] = {
> +  // 0 - In range
> +  {.expected = { .tv_sec = 1, .tv_nsec = 0},
> +   .observed = {.tv_sec = 1, .tv_nsec = 0},
> +   .upper_bound = 1, .lower_bound = 1, .result = 1,
> +  },
> +  // 1 - Out of range
> +  {.expected = { .tv_sec = 1, .tv_nsec = 0},
> +   .observed = {.tv_sec = 2, .tv_nsec = 0},
> +   .upper_bound = 1, .lower_bound = 1, .result = 0,
> +  },
> +  // 2 - Upper Bound
> +  {.expected = { .tv_sec = 1, .tv_nsec = 0},
> +   .observed = {.tv_sec = 2, .tv_nsec = 0},
> +   .upper_bound = 2, .lower_bound = 1, .result = 1,
> +  },
> +  // 3 - Lower Bound
> +  {.expected = { .tv_sec = 1, .tv_nsec = 0},
> +   .observed = {.tv_sec = 0, .tv_nsec = 0},
> +   .upper_bound = 1, .lower_bound = 0, .result = 1,
> +  },
> +  // 4 - Out of range by nanosecs
> +  {.expected = { .tv_sec = 1, .tv_nsec = 0},
> +   .observed = {.tv_sec = 1, .tv_nsec = 500},
> +   .upper_bound = 1, .lower_bound = 1, .result = 0,
> +  },
> +  // 5 - In range by nanosecs
> +  {.expected = { .tv_sec = 1, .tv_nsec = 0},
> +   .observed = {.tv_sec = 1, .tv_nsec = 50000},
> +   .upper_bound = 1.3, .lower_bound = 1, .result = 1,
> +  },
> +  // 6 - Big nanosecs
> +  {.expected = { .tv_sec = 1, .tv_nsec = 0},
> +   .observed = {.tv_sec = 0, .tv_nsec = 4000000},
> +   .upper_bound = 1, .lower_bound = .001, .result = 1,
> +  },
> +  // 7 - In range Negative values
> +  {.expected = { .tv_sec = -1, .tv_nsec = 0},
> +   .observed = {.tv_sec = -1, .tv_nsec = 0},
> +   .upper_bound = 1, .lower_bound = 1, .result = 1,
> +  },
> +  // 8 - Out of range Negative values
> +  {.expected = { .tv_sec = -1, .tv_nsec = 0},
> +   .observed = {.tv_sec = -1, .tv_nsec = 0},
> +   .upper_bound = -1, .lower_bound = -1, .result = 0,
> +  },
> +  // 9 - Negative values with negative nanosecs
> +  {.expected = { .tv_sec = -1, .tv_nsec = 0},
> +   .observed = {.tv_sec = -1, .tv_nsec = -2000},
> +   .upper_bound = 1, .lower_bound = 1, .result = 0,
> +  },
> +  // 10 - Strict bounds
> +  {.expected = { .tv_sec = -1, .tv_nsec = 0},
> +   .observed = {.tv_sec = -1, .tv_nsec = -20000},
> +   .upper_bound = 1.00002, .lower_bound = 1.0000191, .result = 1,
> +  },
> +  // 11 - Strict bounds with loose upper bound
> +  {.expected = { .tv_sec = 1, .tv_nsec = 20000},
> +   .observed = {.tv_sec = 1, .tv_nsec = 30000},
> +   .upper_bound = 1.0000100000, .lower_bound = 1.0000099998, .result = 1,
> +  },
> +  // 12 - Strict bounds with loose lower bound
> +  {.expected = { .tv_sec = 1, .tv_nsec = 20000},
> +   .observed = {.tv_sec = 1, .tv_nsec = 30000},
> +   .upper_bound = 1.0000099999, .lower_bound = 1.00000999979, .result = 1,
> +  },
> +  // 13 - Strict bounds highest precision
> +  {.expected = { .tv_sec = 1, .tv_nsec = 20000},
> +   .observed = {.tv_sec = 1, .tv_nsec = 30000},
> +   .upper_bound = 1.00000999980001, .lower_bound = 1.00000999979999, .result = 1,
> +  },
> +  /* Maximum/Minimum long values  */
> +  // 14
> +  {.expected = { .tv_sec = LONG_MAX, .tv_nsec = LONG_MAX},
> +   .observed = {.tv_sec = LONG_MAX, .tv_nsec = LONG_MAX -1},
> +   .upper_bound = 1, .lower_bound = .9, .result = 1,
> +  },
> +  // 15
> +  {.expected = { .tv_sec = LONG_MAX, .tv_nsec = LONG_MAX},
> +   .observed = {.tv_sec = LONG_MAX, .tv_nsec = LONG_MAX},
> +   .upper_bound = 1, .lower_bound = 1, .result = 1,
> +  },
> +  // 16
> +  {.expected = { .tv_sec = LONG_MAX, .tv_nsec = LONG_MAX},
> +   .observed = {.tv_sec = LONG_MIN, .tv_nsec = LONG_MIN},
> +   .upper_bound = 1, .lower_bound = 1, .result = 0,
> +  },
> +  // 17
> +  {.expected = { .tv_sec = LONG_MIN, .tv_nsec = LONG_MIN},
> +   .observed = {.tv_sec = LONG_MIN, .tv_nsec = LONG_MIN},
> +   .upper_bound = 1, .lower_bound = 1, .result = 1,
> +  },
> +  // 18
> +  {.expected = { .tv_sec = LONG_MIN, .tv_nsec = LONG_MIN},
> +   .observed = {.tv_sec = LONG_MAX, .tv_nsec = LONG_MAX},
> +   .upper_bound = 1, .lower_bound = 1, .result = 0,
> +  }
> +};
> +
> +static int
> +do_test (void)
> +{
> +  int i = 0;
> +
> +  int ntests = sizeof (test_cases) / sizeof (test_cases);
> +  for (i = 0; i < ntests; i++)
> +    {
> +      TEST_COMPARE (support_timespec_check_in_range
> +		    (test_cases[i].expected, test_cases[i].observed,
> +		     test_cases[i].lower_bound,
> +		     test_cases[i].upper_bound), test_cases[i].result);
> +    }
> +  return 0;
> +}

OK.

> +
> +#include <support/test-driver.c>
> diff --git a/time/tst-cpuclock1.c b/time/tst-cpuclock1.c
> index 0120906f23..f9eb054f89 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/timespec.h>

OK.

>  
>  /* This function is intended to rack up both user and system time.  */
>  static void
> @@ -155,16 +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)
> +  /* The bound values are empirically defined by testing this code over high cpu
> +     usage and different nice values.  */
> +  struct timespec diff = timespec_sub (support_timespec_normalize (after),
> +				       support_timespec_normalize (before));
> +  if (!support_timespec_check_in_range (sleeptime, diff, .4,  1.1))

OK.

>      {
>        printf ("before - after %ju.%.9ju outside reasonable range\n",
>  	      (uintmax_t) diff.tv_sec, (uintmax_t) diff.tv_nsec);
> @@ -194,19 +190,14 @@ 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)
> +        /* The bound values are empirically defined by testing this code over
> +           high cpu usage and different nice values.  */
> +	  diff = timespec_sub (support_timespec_normalize (afterns),
> +			       support_timespec_normalize (after));
> +	  if (!support_timespec_check_in_range (sleeptime, diff, .9, 1.2))

OK.

>  	    {
>  	      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;
>  	    }
>  	}
> @@ -240,15 +231,12 @@ do_test (void)
>    /* Should be close to 0.6.  */
>    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)
> +  /* The bound values are empirically defined by testing this code over high cpu
> +     usage and different nice values.  */
> +  diff = timespec_sub (support_timespec_normalize (dead),
> +		       support_timespec_normalize (after));
> +  sleeptime.tv_nsec = 100000000;
> +  if (!support_timespec_check_in_range (sleeptime, diff, .9, 1.2))

OK.

>      {
>        printf ("dead - after %ju.%.9ju outside reasonable range\n",
>  	      (uintmax_t) diff.tv_sec, (uintmax_t) diff.tv_nsec);
>